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Durham E-Theses
Kinetic and equilibrium studies of the reactions of some
aromatic nitro compounds with metal alkoxides
Al-Aruri, Ahmad D. A.
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Al-Aruri, Ahmad D. A. (1981) Kinetic and equilibrium studies of the reactions of some aromatic nitro
compounds with metal alkoxides, Durham theses, Durham University. Available at Durham E-ThesesOnline: http://etheses.dur.ac.uk/7552/
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Academic Support O�ce, Durham University, University O�ce, Old Elvet, Durham DH1 3HPe-mail: [email protected] Tel: +44 0191 334 6107
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2
KINETIC AND EQUILIBRIUM STUDIES OF
THE REACTIONS OF SOME AROMATIC
NITRO COMPOUNDS WITH METAL AIKOXIDES
by
The copyright of this thesis rests with the author.
No quotation from it should be published without
his prior written consent and information derived
from it should be acknowledged.
Ahmad D.A. A l - A r u r i , B.Sc. (Kuwait)
(Colltrigwood College)
A t h e s i s submitted f o r the degree of Ph.D. i n the U n i v e r s i t y o f Durham,
September, 1981
To my parents
DECLARATION
The m a t e r i a l i n t h i s t h e s i s i s the r e s u l t o f research c a r r i e d o ut
i n the Department o f Chemistry, U n i v e r s i t y o f Durham, between October
1978 and J u l y 1981. I t has not been submitted f o r any other degree,
and i s the author's own work, except where acknowledged by reference.
PUBLICATIONS
Sane o f the r e s u l t s described i n t h i s t h e s i s have been published
the f o l l o w i n g papers.
The S t a b i l i t i e s o f Meisenheimer Complexes. P a r t 20.
" K i n e t i c and E q u i l i b r i u m Data f o r the Reaction o f Some Aromatic
Nitro-compounds w i t h Propoxide Ions i n p r o p a n - l - o l "
by
A.D.A. A l - A r u r i and M.R. Crampton , J. Chem. Res., (S) 140;
(M) 2157, (1980).
The S t a b i l i t i e s o f Meisenheimer Complexes, Part 26.
"The r e a c t i o n s o f some Aromatic Nitro-compounds w i t h Base i n t -
Bu y l Alcohol-Water M i x t u r e s "
by
A.D.A. A l - A r u r i and M.R. Crampton , J.C.S., Per k i n I I , 807,
(1981).
ACKNOWLEDGEMENTS
I t i s w i t h g r a t i t u d e t h a t I thank my Supervisor, Dr. M.R. Crampton,
f o r h i s generous help, and constant encouragement.
My thanks are also due t o many o f the t e c h n i c a l s t a f f o f the
Department w i t h o u t whose help some o f t h e work would not have been
p o s s i b l e .
F i n a l l y , May I thank Mrs. M. Chipchase f o r t y p i n g t h i s t h e s i s .
C O N T E N T S
Page CHAPTER 1 - I n t r o d u c t i o n 1
CHAPTER 2 - Experimental 54
CHAPTER 3 - K i n e t i c and E q u i l i b r i u m Data f o r the Reactions o f some Aromatic Compounds w i t h Propoxide Ions i n Propan-l-ol
I n t r o d u c t i o n 65
Experimental 66
Results and Discussion 66
(a) l-Propoxy-2,4-dinitro-6-propoxy carbonyl
benzene 68
(b) l-Propoxy-2,4-dinitro-6-Chlorobenzene 70
( c ) l-Propoxy-2,4-dinitrobenzene 71
(d) 1,3,5-Trinitrobenzene 76
(e) l-Propoxy-2,4,6-trinitrobenzene 77
( f ) l-Chloro-2,4-Dinitrobenzene 81
Ion A s s o c i a t i o n 81 Comparison of Propoxide Adducts w i t h those from other alkoxides 84
S t r u c t u r a l Study Using N.M.R. technique 87
CHAPTER 4 - The Reactions o f Three N i t r o Aromatic Compounds w i t h Tetramethylammonium Hydroxide and Metal Butoxides i n t-Butanol Containing Water
I n t r o d u c t i o n " 89
Experimental 90
Part I : Reaction w i t h Tetramethylammonium Hydroxide
Results and Discussion
( a ) 1,3,5-Trinitrobenzene 91 (b) l-Chloro-2,4-dinitrobenzene 94 ( c ) l - C h l o r o - 2 , 4 , 6 - t r i n i t r o b e n z e n e 97
Page Pa r t I I Reactions w i t h A l k a l i - M e t a l Butoxides
( a ) 1,3,5-Trinitrobenzene 103
(b ) l-Chloro-2,4-Dinitrobenzene 105
( c ) l-Chloro-2,4,6-Trinitrobenzene 109
Conclusion 114
CHAPTER 5 - Cation-complexing o f o-Adducts i n
Concentrated Metal Methoxide S o l u t i o n s
I n t r o d u c t i o n 115
Experimental 116
Results and Discussion
(a ) 2-Methoxy-3,5-Dinitrobenzoic A c i d 116 (b) 2 , 4 , 6 - T r i n i t r o a n i s o l e 121 ( c ) N,N-Dimethylpicramide 122 ( d ) l-(2'-Hydroxyethoxy-2,4,6-trinitrobenzene) 124 (e ) N, Methylpicramide 129
( f ) 2 , 4 , 6 - T r i n i t r o a n i l i n e (picramide) 136
Conclusions 145
Appendix 148
References 155
ABSTRACT
K i n e t i c and e q u i l i b r i u m measurements have been made f o r o-adduct
formation from propoxide ions i n p r o p a n - l - o l w i t h 1,3,5-trinitrobenzene
and a s e r i e s of l-propoxy-2,4-dinitro-6-x-benzenes ( x = NOg, CI, CC^Pr, H).
The r e s u l t s are compared w i t h those f o r s i m i l a r a d d i t i o n s of other
a l k o x i d e ions. There i s evidence f o r s t r o n g a s s o c i a t i o n w i t h sodium
ions o f the 1,1-dipropoxy adducts, but adducts formed by base a d d i t i o n s
a t u n s u b s t i t u t e d r i n g p o s i t i o n s are not s t r o n g l y associated. I n the
n u c l e o p h i l i c s u b s t i t u t i o n r e a c t i o n w i t h l-chloro-2,4-dinitrobenzene
f r e e propoxide ions show g r e a t e r r e a c t i v i t y than sodium propoxide ion
p a i r s .
Rate and e q u i l i b r i u m s t u d i e s are re p o r t e d f o r t h e r e a c t i o n s of
three aromatic nitro-compounds w i t h tetramethylarrmonium hydroxide i n t -
b u t y l a l c o h o l water mixtures. There i s evidence t h a t the r e a c t i v e
n u c l e o p h i l e i s the hydroxide ion r a t h e r than t h e t - b u t o x i d e i o n . The
r e a c t i o n o f 1,3,5-trinitrobenzene i n t h i s system leads t o a a-adduct,
w h i l e l-chloro-2,4-dinitrobenzene gives 2 , 4 - d i n i t r o p h e n o l . That the
r a t e s o f both these r e a c t i o n s f a l l s r a p i d l y w i t h i n c r e a s i n g water content
i s a t t r i b u t e d mainly t o the good s o l v a t i o n o f the hydroxide i o n by
water. I n c o n t r a s t t h e r a t e o f formation o f p i c r i c a c i d from p i c r y l
c h l o r i d e increases w i t h water content due t o i n i t i a l f ormation of the
3-hydroxy adduct. S i m i l a r s t u d i e s have been made using sodium and/or
potassium butoxide The i n t e r p r e t a t i o n here i s complicated by
a s s o c i a t i o n w i t h anions o f the a l k a l i metal c a t i o n s .
I n the presence o f methoxide ions i n methanol 2-methoxy-3,5-dinitro-
benzoic a c i d gives a a-adduct. Using t h i s r e a c t i o n , a c i d i t y f u n c t i o n s
f o r l i t h i u m , sodium and potassium methoxide s o l u t i o n s have been def i n e d .
The observed b a s i c i t y order : sodium methoxide > potassium methoxide >
l i t h i u m methoxide may de r i v e from s p e c i f i c i n t e r a c t i o n s o f t h e a l k a l i
c a t i o n s w i t h the o-adduct. Using U . V . / v i s i b l e data the r e v e r s i b l e
e q u i l i b r i a between l - x - 2 , 4 , 6 - t r i n i t r o b e n z e n e s ( x = NMe,.,, NHMe, NH 2 >
QM8 o r CCH9CH O) and a l k a l i metal methoxides have been i n v e s t i g a t e d .
Usually 1:1, 1:2 and 1:3 i n t e r a c t i o n s are observed. One conclusion
i s t h a t i n general 1:2 and 1:3 adducts associate more s t r o n g l y w i t h
sodium ions than w i t h potassium ions o r w i t h l i t h i u m ions.
CHAPTER 1
INTRODUCTION
1. H i s t o r y 1 2 Hepp i n (1882) and Lobry de Bruyn i n (1890) succeeded i n
pr e p a r i n g and se p a r a t i n g some coloured complexes by the a d d i t i o n
of bases t o s o l u t i o n s of aromatic t r i n i t r o compounds. Lobry de
Bruyn and van Leent (1895) prepared other complexes, o t h e r s f o l l o w e d
them^ - 9, Meisenheimer^ (1902) gave a str o n g piece o f chemical
evidence f o r t h e s t r u c t u r e s formed when he obtained the same complexes
by a d d i t i o n of potassium methoxide t o 2 , 4 , 6 - t r i n i t r o p h e n e t o l e and
potassium ethoxide t o 2 , 4 , 6 - t r i n i t r o a n i s o l e , a c i d i f i c a t i o n gave a
m i x t u r e of the phenetole and the a n i s o l e d e r i v a t i v e s . This l e d him
t o conclude t h a t these complexes were formed by covalent a d d i t i o n
o f base a t CI t o g i v e (1.1) r a t h e r than a d d i t i o n a t the unsub-
s t i t u t e d 3 - p o s i t i o n t o g i v e ( 1 . 2 ) .
R O y O R
O N V ^ Y
H
NCL
H
( l . l )
K O N
( 1.2)
Such complexes are ccnmonly termed Meisenheimer o r Jackson Meisenheimer
complexes.
The present-day r e p r e s e n t a t i o n f o r Meisenheimer complexes would
be ( 1 . 3 ) , where t h e negative charge i s d e l o c a l i s e d about the r i n g
and t h e n i t r o - g r o u p s .
2 7 NOV 1981
- 2 -
OR RO NO O N
H NO
(1.3)
2. Aromatic n i t r o compounds
Aromatic n i t r o compounds which are a c t i v a t e d by one or more
n i t r o groups may r e a c t r e v e r s i b l y w i t h bases by three main routes
( i ) Proton a b s t r a c t i o n
A c t i v i t a t e d aromatic compounds such as 1,3,5-trinitrobenzene
and 1,3-dinitrobenzene w i l l exchange r i n g hydrogens f o r deuterium 12-14
or t r i t i u m i n basic s o l u t i o n s . The exchange i s l i k e l y t o 134 142
i n v o l v e carbanions such as ( 1 . 4 ) . Recent ' k i n e t i c r e s u l t s
i n d i c a t e t h a t t h e r a t e of exchange from t h e 2 - p o s i t i o n o f 1,3-
dinitrobenzene (1.5) i s considerably more r a p i d than from the 4-
p o s i t i o n . T r i t i u m n.m.r. st u d i e s i n d i c a t e t h a t exchange i n 1,3-
di n i t r o n a p h t h a l e n e (1.6) occurs a t the 4 - p o s i t i o n .
NO NO NO
f x O N NO NO
(1.4 (1.5) (1.6)
- 3 -
( i i ) E l e c t r o n t r a n s f e r
A p a r t i a l t r a n s f e r , through o r b i t a l o v e r l a p , of e l e c t r o n i c
charge from t h e base (Y : or Y~) t o the aromatic nucleus depleted
o f T T - e l e c t r o n d e n s i t y owing t o t h e e l e c t r o n e g a t i v e n i t r o -
s u b s t i t u e n t s gives r i s e t o charge-transfer complexes known as donor-15
acceptor o r TT-complexes
( 1 . 7 f
NO 2-Y:
A f u r t h e r degree of i n t e r a c t i o n may lead t o an e l e c t r o n from Y
becoming completely t r a n s f e r r e d t o the n i t r o compound, i n which 11 15
case a r a d i c a l anion (1.8) i s produced '
H r NO
NO H H
°2 (1.8)
Such anions have been detected i n basic s o l u t i o n s o f n i t r o -
toluenes and 1,3-dinitrobenzene and may be p r e l i m i n a r y i n t e r
mediates i n c e r t a i n n u c l e o p h i l i c aromatic s u b s t i t u t i o n r e a c t i o n s .
I n c o n t r a s t t o t h e e l e c t r o n - t r a n s f e r process i s the i n t e r a c t i o n by
which t h e unshared e l e c t r o n p a i r o f Y~ i s used i n formation o f a
- 4 -
covalent bond t o an aromatic carbon atom. The r e s u l t i n g species 19
i s then a sigma-complex
Both proton a b s t r a c t i o n and e l e c t r o n t r a n s f e r have been found
t o make a r e l a t i v e l y small c o n t r i b u t i o n i n aromatic compounds
a c t i v a t e d by t h r e e e l e c t r o n withdrawing groups,
( i i i ) o Adduct Formation
This i n v o l v e s covalent bond f o r m a t i o n between the a t t a c k i n g
n u c l e o p h i l e and a r i n g carbon atom. The very wide scope o f these
r e a c t i o n s i s described i n d e t a i l l a t e r i n t h e i n t r o d u c t i o n . When the
s u b s t r a t e contains a l e a v i n g group then n u c l e o p h i l i c s u b s t i t u t i o n may
occur.
Aromatic N u c l e o p h i l i c S u b s t i t u t i o n
There are s e v e r a l p o s s i b l e mechanisms f o r n u c l e o p h i l i c sub
s t i t u t i o n r e a c t i o n s .
( i ) The Sj^l Mechanism This mechanism i s r a r e f o r s u b s t i t u t i o n a t aromatic carbon atoms,
19 20
and k i n e t i c a l l y i s a f i r s t order process ' . The thermal decom
p o s i t i o n o f aromatic diazonium ions i n aqueous s o l u t i o n i s
k i n e t i c a l l y f i r s t order, and t h e r a t e o f r e a c t i o n ( a p a r t from s o l v e n t
and s a l t e f f e c t ) i s not a l t e r e d upon a d d i t i o n of methanol o r of c h l o r i d e ions, (equations 1.1 and 1.2).
. + slow . +
ArN 2 » Ar + N 2 1-1
A r + + X" f a S \ ArX 1.2
( i i ) The S AR Mechanism The great m a j o r i t y o f aromatic m u c l e o p h i l i c s u b s t i t u t i o n s occur
by a bimolecular mechanism. Second-order k i n e t i c s , f i r s t order i n 19 21
both s u b s t r a t e and reagent are r e g u l a r l y observed ' 22
A two-step i n t e r m e d i a t e complex mechanism theory has taken
- 5 -
precedence over t h e o l d one-step mechanism o f synchronous bond 23 °4
forma t i o n and bond breaking . (scheme 1.1).
Y
NO NO NO + Y + X
NO NO NO
scheme 1.1
The Sj AR mechanism g e n e r a l l y c o n s i s t s o f f o r m a t i o n of an i n t e r
mediate complex i n t h e f i r s t step and t h e departure o f the le a v i n g
group i n the second step.
T his mechanism was j u s t i f i e d by p r e p a r i n g one o f these i n t e r -2(
mediates(A Meisenheimer complex i n 1882) as described by the scheme
1.2
OEt
NO NO NO 0 N O N O N 4 KOMe KOEt
NO NO N 0 O
K scheme 1.2
When the n u c l e o p h i l i c a t t a c k occurs at an atom other than t h a t
c a r r y i n g the l e a v i n g group then c i n e - s u b s t i t u t i o n s ( s u b s t i t u t i o n w i t h
rearrangement, where the e n e t e r i n g group comes i n o r t h o t o t h e
l e a v i n g group) and t e l e - s u b s t i t u t i o n s (where t h e e n t e r i n g group takes
up a p o s i t i o n more than one atom away from t h e atom t o which t h e
l e a v i n g group was attached) may occur.
An example o f t h i s i s the r e a c t i o n of 2 , 4 - d i n i t r o a n i l i n e w i t h
p i p e r i d i n e which gives three isomeric n i t r o p i p e r i d i n o a n i l i n e s as
f o l l o w s 2 6 (scheme 1.3)
NH
NC> 29% ( c i n e ) o N
NH
NH
BASIC 23% —* (normal) ALUMINA N NO H
Scheme 1.3
\ NH N NO / 12%
( t e l e )
- 7 -
In t r a m o l e c u l a r s u b s t i t u t i o n of N-Qo-(4-nitrophenoxy)alkyl] 27
a n i l i n e has been described by the f o l l o w i n g mechanism (scheme 1.4).
-c
DEACTIVATION < —
O
NH o - 6 NO
'l c — c
-H +
N f c 2 H 5 ) 3
1 O N -
Q N 0 2
scheme 1.4
C a t a l y s t s play a notable r o l e i n n u c l e o p h i l i c s u b s t i t u t i o n s , an
example being t h e use of t e t r a b i s - ( t r i p h e n y l phosphine) palladium (o) OCL no or:
c a t a l y s t w i t h alumina (equations 1.3 and 1.4)
ArX + Pd(o) > ArPdX 1.3
ArPdX + RS" ^ ArSR + Pd(o) + X" 1.4
N u c l e o p h i l i c s u b s t i t u t i o n s i n h e t e r o c y c l i c systems have been 21 25 29
reviewed by many researchers ' '
- 8 -
Many factors a f f e c t the aromatic nucleophilic substitutions and
such reactions are often favoured i n dipolar aprotic solvents.
Activation by a n i t r o group requires conjugation between the sub-+ y o
s t i t u e n t and the reaction s i t e . This i n turn requires that the N ^ q
group i s nearly coplanar with the benzene r i n g , and i f t h i s i s
prevented, by a bulky group, the nucleophilic attack w i l l be reduced,'
t h i s i s an example of the s t e r i c factor. The nature of both the 21
substrate and nucleophile are also e f f e c t i v e factors i n t h i s
mechanism.
( i i i ) The Elimination-addition mechanism
This mechanism proceeds via Aryne species, which are usually 30
generated by the action of a very strong base. Bunnett discussed
the i d e n t i f i c a t i o n of such species: (1.9)
(1.9)
Since arynes are usually generated by basic reagents, themselves
nucleophiles, the only nucleophiles whose additions to arynes have
been observed are those which can compete successfully with the aryne-
generating bases. These good competitors are anions with negative
charge on carbon, nitrogen, or sulphur. Oxygen anions, such as CH O
are weak competitors.
- 9 -
The reaction of 2-bromo-4-methylbenzophenone with potassium amide i n ammonia i s a recent example of t h i s mechanism and gives species such as (1.10).
Here addition of a proton to form a r y l bromide competes w i t h elimination 31
of halide ion to give the aryne
( i v ) Free-Radical Mechanism
The S ^ l mechanism which involves free radical intermediates
provides a means fo r nucleophilic s u b s t i t u t i o n i n substrates which are 135
not activated by strongly electron-withdrawing groups. A mechanism
involving radicals may also be involved i n the reaction of 1-chloro-
2,4-dinitrobenzene w i t h potassium isopropoxide i n isopropanol : benzene
mixtures. The main product of reaction i s l-isopropoxy-2,4-dinitro
benzene. However i n the presence of crown-ethers substantial amounts
of 2,4-dinitrophenol are formed and the k i n e t i c order i n base i s less
than unity. The addition of the complexing agent makes i t possible for
separation of the ion-pairs formed between thea-adduct and the cation
to occur. The unshielded negative charge of the complex makes i t more
reactive and more prone to lose one electron.
The mechanism can be described by equations : 1.5 and 1.6.
Arx + RO~ >• A? / X 1.5
CH
(1.10)
x OR OR Ar + ArX
X AT + ArX 1 1.6
OR
- 10 -
Then the fat e of the ra d i c a l anion of the halogenobenzene, can be described by : (equations 1.7 - 1.9)
ArX~- Ar' + X~ 1.7
Ar- + R0~ ± ArOR~* 1.8
ArOR"- ^ ArO~ + R' 1.9
This can explain the p o s s i b i l i t y that a fragment, formed from reaction
of a r y l ethers with a l k a l i metals, may give phenoxide and an a l k y l
r a d i c a l . 11 91 19 Covalent (o-) complexes 1' x' °
Are formed due t o charge transfer between two types of molecules
i n which one of them acts as an electron acceptor and the other as an
electron donor, forming a f u l l bond. Streitweiser concludes from his
calculations that a-complex i s a good model f o r the t r a n s i t i o n state i n
an aromatic nucleophilic s u b s t i t u t i o n reaction.
Meisenheimer Complexes
Are simply anionic sigma complexes (or adducts) formed from the
addition of nucleophiles t o activated aromatic substrates. Given below
are some examples of d i f f e r e n t types of adducts c l a s s i f i e d according
to the nature of the nucleophile. As reviews of o-adducts are available
most emphasis has been put on recent work.
( i ) With Alkoxides and Hydroxide Ions
Crampton and Gold i d e n t i f i e d unambiguously by N.M.R. spectroscopy
the structure of the adduct formed 1,3,5-trinitrobenzene with potassium
methoxide i n DMSO as (1.11 )
1:1 adduct
C1-11)
- 11 -
Hie parent shews a single resonance f o r the three equivalent hydrogens
at 9.2 p.p.m. Complex formation results i n a covalency change for the 2 3
hydrogen at C-2 from sp t o sp bonding, and the resonance i s shifted to
high f i e l d ( 6.14 p.p.m), while the other two equivalent hydrogens at
C-4 and C-6 show a smaller s h i f t to 8.42 p.p.m. The three methoxyl
protons give a band at 3.10 p.p.m. Similar observations have been made 35
i n a c e t o n i t r i l e and dimethyl formamide , taking the solvent effe c t i n 36
consideration. For the same parent i n DMSO, Foster and Fyfe carried out similar measurements f o r ethoxide and n-butoxide adducts. Another comparative N.M.R. study with thioethoxide and thiophenoxide ions has
37 been reported
At high nucleophile concentrations 1:2 adducts may be formed.
V i s i b l e spectra have been used t o distinguish between the 1:1 adduct
from 1,3,5-trinitrobenzene which has two absorptions and the 1:2 adduct
which has a single absorption''""''. Kinetic analysis for the addition of
aqueous sodium hydroxide t o trinitrobenzene reveals two reversible
e q u i l i b r i a . The f i r s t involving the 1:1 adduct, the second produces the
1:2 adduct 1 1 (1.12)
OH H
NO O N 1:2 adduct
H
( 1.12)
- 12 -
N.M.R. spectra supported the structure (1.13) formed from potassium methoxide and 2,4,6-trinitroanisole i n DMSO where a single band i s
observed f o r the s i x methoxyl protons indicaitng t h e i r equivalence.
This adduct i s preceeded by a less stable short-lived isomer where
methoxide ions attach C-3. Similar adducts containing various alkoxy 36 38
groups have been studied. '
OCH C H O
NO O N
H H
N 0 2
(1.13)
An N.M.R. spectrum has been taken
methoxide ions have been found to
the thermodynamically more stable
A di-adduct (1.14) formed at
proposed from an N.M.R. study .
for the C-3 adduct. Methanol and
enhance the rate of isomerisation to
C-l adduct 1 4.
high alkoxide concentrations has been
MeO OMe
NO.
H OMe
NO
(1.14)
Another colourless species has been a t t r i b u t e d to tri-adduct at very
high alkoxide concentrations (1.15).
- 13 -
O M e MeO
O N NO
H H O M e M e O
NO (1.15)
As part of the present work a k i n e t i c study has been made of the reaction
of propoxide ions i n propanol w i t h 1,3,5-trinitrobenzene and a series
of l-propoxy-2,4-dinitro-6-substituted benzene. With l-propoxy-2,4,6-
trinitrobenzene the scheme below was shown to apply.
OPr
NO O N
H \ OPr
NO OPr
O N PrO'-f
NO O N NO
NO
scheme 1.5
- 14 -Other k i n e t i c studies f o r reactions of sim i l a r substrates with methoxide
42 i n methanol , ethoxide i n ethanol and tert-butoxide i n tert-butanol-
43
water mixtures have been made.
A recent study by N.M.R. of the reaction of ethoxide ions with e t h y l
t h i o p i c r a t e i n DMSO shows that the i n i t i a l product i s 3-ethoxy ethyl 34
thiop i c r a t e and t h i s i s followed by the su b s t i t u t i o n reactions (scheme
1.6) SEt SEt
NO O N NO 2
4- OEt H
OEt NO NO
DECAY 8Y DISSOCIATIVE MECHANISM
O SEt
NO O.N O N
NOu Q NO
Scheme 1.6
However attack of ethanethiolate ions i n ethylpicrate yields the
isomeric adducts (at C-3 or C-l) (1.16) and (1.17).
OEt E t O SEt NO 0_N NO O N
C3D
H SEt
NO (1.17) (1.16)
- 15 -
The reaction of alkoxide ions with 2,4,6-trinitrotoluene (TNT) re s u l t s i n proton abstraction, a-complex formation and radical anion formation 4 4. (1.18 - 1.21).
CH CH CH H C OR
NO NO. O N NO O N O N NO.
H OR
NO NOp (1.18) (1.19) (1.20) (1.21)
a-complex rad i c a l anion
Although, reducing the number of nitrogroups a c t i v a t i n g the aromatic
r i n g reduces the tendency t o form covalent adducts,crystalline adducts
such as (1.22) have been isolated from reactions of dinitroanisoles
with alkoxides. The structure has been confirmed by N.M.R. spectroscopy 36,45,46.
R O . .OR
NO„
(R = Rs=Alkyl,X = H)
(1.22)
The addition of methanolic sodium methoxide to a DMSO solution of
2,4-dinitroanisole doubles the band due to methoxyl protons and s h i f t s
i t f r an 4.10 p.p.m i n the parent up to 2.94 p.p.m., which proves the
i d e n t i t y of the methoxyl groups i n the complex. Small s h i f t s to high
f i e l d due to r i n g protons have been observed. Another piece of
evidence showing that the addition occurs at CI comes from the spin-
16 -
spin coupling constants which are not affected since no covalency change 47
occurs at a r i n g carbon carrying hydrogen. Byrne et a l observed
similar spectra from dissolving a s o l i d dinitroanisole s a l t i n DMSO.
The same thing has been proved by N.M.R. by methoxide addition to 2,6-
din i t r o a n i s o l e . The extent of conversion of the picrate ion ( p i c r i c
acid exists as picrate ion i n d i l u t e aqueous solution of sodium hydro-O 1 1
xide due to i t s high acidity,X 360OA) to complex depends on a 48
high power of base concentration . N.M.R. measurements proved that 49 50
such reaction involves more than one hydroxide ion, ' giving the
structure (1.23)
O N <
N 0 2
(1.23)
There i s a strong u p f i e l d s h i f t of the r i n g proton band from 8.8 p.p.m
i n the picrate ion to 6.1 p.p.m i n concentrated sodium hydroxide solution.
With sodium methoxide i n methanol, a change i n v i s i b l e spectrum
indicates the p o s s i b i l i t y of the addition of one, and two methoxide
ions at r i n g carbons carrying hydrogen. The addition of methanolic
sodium methoxide to 1,3-dinitrobenzene i n DMSO produces a red solution
(^ „ 520 nm) giving the adduct (1.24) whose structure has been
confirmed by N.M.R.12'46.
- 17 -
O M e H
H NO
H H
NO (1.24
The amino group i n 2,4-dinitroaniline loses a proton i n methanolic
DMSO. N.M.R. showed no change i n the pattern of r i n g protons i n the
presence of base, except a s h i f t to high f i e l d which i s consistent with
fast exchange between the parent and Bronsted base (proton acceptor), 52
and there i s no evidence f o r methoxide addition. Gold and Rochester
suggested from a study using v i s i b l e spectroscopy that picramide and i t s
N-substituted derivatives produce two species, one due t o proton loss
from the amino-group (R = H, a l k y l , phenyl) (1.25) and
the other due to attack of alkoxide at C-3. (1.26).
NR
O N NO NO O N
H H H H OR
NO o 2 (1.26) (1.25)
Kinetic study of the reaction i n methanol with methoxide ions indicates
a very rapid process (measurable by T-jump) which i s a t t r i b u t e d to
proton transfer to give the conjugate base, and to a slower process
(measurable by stopped-flow) a t t r i b u t e d to methoxide addition at
the unsubstituted 3-position (scheme 1.7).
- 18 -
R \ N
NO O N SB
R H N NO
O N NO + O M e H R
X* ° 2N
NO NO
H OMe
NO
complex
scheme 1.7
These interactions have been confirmed by N.M.R. i n DMSO-methanol 53
solvent . At high base concentration the 1:2 adduct of N,N-dimethyl-
picramide i s formed and v i s i b l e spectra have been taken f o r the 1:1 and
1:2 adducts 5 4. (1.27)
H C CH N
O N NO
H H OCH C H O
N O 1:2 COMPLEX
(1.27)
- 19 -
The conclusions are that the reactions of picramide and N-alkyl
picramides with methoxide ions involve very rapid proton transfer t o
give the conjugate base and a slower process fo r addition at C-3. 54 5^
At high base concentrations 1:2 and 1:3 complexes are observed ' . Gold and Rochester noted the unusual s t a b i l i t y of the 1:2 adduct formed
56 from N,N-dimethyl picramide w i t h sodium hydroxide i n water . The
reaction of N,N-dipropyl-2,6-dinitro-4-(trifluoromethyl) a n i l i n e with
hydroxide ions i n water DMSO mixtures results i n the formation of the
3-hydroxy adduct. There i s evidence that, as with related compounds 57
ioni z a t i o n of the added hydroxyl group occurs to give the dianion
(1.28)
Pr Pr V/ N
NO O N
H
O NO
(1.28)
Intramolecular attack may occur to y i e l d the spiro a-complex when
methoxide i s added to l-(2-hydroxyethoxy)-2,4,6-trinitrobenzene according
to the scheme 1 . 8 1 1 > 3 2 - 3 8 ' 5 8
CH O - C H C H O H
O O O N 2 1 T
O N NO
C H O H H
NO NO
scheme 1.8
- 20 -
Two bands are observed i n the N.M.R. spectrum f o r the complex at 2
8.7 p.p.m due to the sp r i n g proton and at 4.3 p.p.m due to the equivalent 59
methylene protons. Drozd and co-workers have i d e n t i f i e d a number of
spiro-complexes including (1.29) formed from an o-hydroxylphenyl
picramide derivative.
Q NMe
NO O N
N 0 2
(1.29)
Meisenheimer prepared and separated a s o l i d c r y t a l l i n e s a l t from 9-
nitroanthracene and potassium methoxide. He proposed the structure
(1.30) for the adduct depending on elemental analysis res u l t s . This 60
structure has been confirmed by N.M.R. study The change i n 2 3
hybridization of the C-10 atom from sp to sp , results i n a resonance
s h i f t from 8.93 p.p.m i n nitroanthracene t o 4.93 p.p.m. i n the complex. H
NOg (1.30)
- 21 -
Alkoxide addition at C-l i n 2,4-dinitro-l-methoxynaphthalene has been confirmed by N.M.R. ' and yields the structure (1.31).
e NO
i
H
( 1 . 3 1 ) n O
A study' " using v i s i b l e and infra-red spectroscopy has been reported
for methoxide addition to l-piperidino-2,4-disubstituted naphthalenes
(1.32).
o X = NCL,CN X
Y = NCL.CN
Y (1.32)
The aza group,-N=, i n a heterocychic system behaves s i m i l a r l y to a n i t r o
group i n an aromatic r i n g , i n that both activate the r i n g to nucleophilic 62
s u b s t i t u t i o n . However, the s t e r i c requirements of the r i n g nitrogen
are considerably reduced r e l a t i v e to a n i t r o group. 3,5-dinitropyridine
w i t h sodium methoxide i n DMSO gives the following Meisenheimer adducts 63 64
(1.33) and (1.34) whose structures have been confirmed by N.M.R. '
- 22 -
H H v ,OMe
O N> 2 >NO„
-H
(1.33)
O N 2
H'
(1.34)
NO.
•H
Also the following reaction (scheme 1.9) has been confiimed by
N.M.R63'64.
O M e
OMe O M e
+ O M e
M e O v •OMe
NO, O Nn 2
"A/
Scheme 1.9
Addition of methoxide ions to 2-methoxy- 5-nitropyrimidine gave (1.35)
NO.
4 .
1.35)
- 23 -
and with 5-nitropyrimidine (1.36) adduct was formed
N
W O M e (1.36)
while w i t h 4-methoxy- 5-nitropyrimidine, the following species was
formed (1.37).
O M e
(1.37)
Steric e f f e c t s are also much less important i n f i v e membered hetero-
c y c l i c rings r e l a t i v e t o benzene derivations
The formation of the thiophen a-adduct (1.38) i n DM30 has been
reported*^.
NO OC
" 3 H OCH
O (1.38)
- 24 -
Recently evidence f o r the formation of the thiophen product (1.39)
during reaction of 4-nitro-2-thenylidene diacetate with 2 - n i t r o -68
propan-2-ide ions has been reported
O
H
M a r
NO. 2(1.39)
C H O
5-azacinnoline (1.40) has been found t o react with hard bases (having
a low ionization p o t e n t i a l ) t o give the anion radical and with s o f t 69
bases (having a high ionization p o t e n t i a l ) t o give the a-complex
N
N (1.40)
( i i ) With Carbon Bases
Carbon bases are organic compounds which, when treated with a base,
undergo ionisation by cleavage of a carbon-hydrogen bond to give
carbanions. Generally solutions of 1,3,5-trinitrobenzene and t r i e t h y -
lamine i n ketonic solvents give complexes where the ketonate ion i s
slowly generated by proton transfer t o the amine (equation 1.10).
NR + CHRCOR ^ "CRCOR + NHR* 1.10 TO 71
The N.M.R. ' spectrin i s i n accord with t h i s structure (1.41)
showing the absence of a bond from C-l to oxygen and of a coupling
constant ( J = 3-6 cps) between H c ^ n b
- 25 -
O
(1.41)
R c W
O N NO
H a H H
N O
p + H 2 N ( C 2 H 5 ) 2
A z w i t t e r i o n i c complex (1.42) has been characterized by N.M.R., which
forms when triethylamine i s added to solution of 1,3,5-trinitrobenzene 72
i n a c r y l o n i t r i l e . (Zwitterion i s a dipolar ion, i t i s a product of
reaction between an acidic group and a basic group that form part of the
same molecule).
N.M.R. indicates the presence of the complex (1.43) i n an acetone 60 2
solution of p i c r y l chloride containing triethylamine . The sp
proton give a t r i p l e t centered at 5.2 p.p.m. (J = 6 cps).
CO
1 / H \ y C - C N
O N NO
(1.42 N O
O . N NOp
C
NO
H C H C O C H ' 2 :
(1-43)
- 26 -
In acetone solutions of N,N-dlmethyl picramide containing a large
excess of triethylamine there i s NMR evidence for the a-complex 0 0
(1.44).
H v / H C O C K
2N s > r N ? NO O N
H ( C H-sLN HCOCH
NO
(1.44)
The interaction of aromatic nitroconpounds with ketones in ketone-73
water or similar solvent mixtures results in the Janovsky reaction .
(This i s a colour forming reaction between carbonyl compounds, especially
aliphatic aldehydes and ketones, and poly-nitrobenzene compounds).
One of these reactions i s that of 1,3-dinitrobenzene with alkaline 73-75
acetone. Suggestions followed by chemical and spectroscopic
evidence supported the structure (1.45). Hv / -HOOCH
H NO
H H NO
(1.45)
N.M.R. measurements indicate the formation of the adduct (1.46)
when sodium methoxide i s added to 1,3-dinitrobenzene in a solvent of
DMSO/nitromethane (60/40 ) (v/v).
- 27 -
HNO H
NO
NO
(1.46) Similarly, there i s N.M.R. evidence from the formation from 2,4-
dinitronaphthalene of (1.47) i n acetone containing triethylamine and 78
(1.48) i n nitrcmethane containing triethylamine .
C H C O C H 2 3 NO-
, C H 2 N 0 2
(1.47) (1.48)
N.M.R. studies show that 3-5-dinitrop.yridine reacts w i t h base
i n acetone t o give a mixture of the following structures .
H X C H 2 C O C H 3 H X C h 2 C ° C H 3 H w C H C O C K
2 • ; O N NO
ff
N 0 2 ~ P R E D O M I N A T I N G S P E C I E S
(1.49) (1.50) 13 CNMR has been used to give some information about the structure of
the very stable complex formed from 1,3,5-trinitrobenzene and cyclo-
pentanone. The unusually low f i e l d p o s i t i o n of the carbonyl carbon
i n the complex, r e l a t i v e t o other complexes, indicates a highly
- 28 -
polarized 0 0 function as shown i n structure (1.51).
(1.51)
H H O N
N O
N.M.R., I.R. and U.V. spectroscopy confirmed structures of the sigma
complexes of 5-nitropyrimidine and i t s methoxy derivatives with
acetonate anion. One of these separated s a l t s i s formed by the reaction
i n scheme 1.10.
H X! HCOMe NO NO MefO
K + H O K O H
M e O M e O N
Scheme 1.10
( i i i ) With Amines
The addition of ammonia, methyl amine, dimethyl amine, 80 81
diethylamine and piperidine t o DMSO solutions ' of 1 , 3 , 5 - t r i n i t r o -
benzene can be explained by the equation 1.11.
R R H N O N N O
if NR R j f i N H + 1,3,5-TNB iH NRR
v : N O
1.11
- 29 -
3 N.M.R. studies show a large s h i f t t o high f i e l d f o r the sp hybridised
carbon atom as i n case of alkoxide adducts, but the absence of coupling 32
( i . e . Jgp 2 gp3 = °) i s i n contrast with alkoxide adducts (J 1 cps) 81
This has been a t t r i b u t e d t o the short l i f e t i m e f o r amine complexes .
1,3,5-Trinitrobenzene gives more intense colour w i t h amnonia, primary
amines and secondary amine than w i t h t e r t i a r y amines, since with 82
t e r t i a r y amines only z w i t t e r i o n formation i s l i k e l y . Amines may add 83
to C-l i n p i c r y l ethers, an example i s the neutral complex (1.52)
formed at low temperature, and when the para n i t r o group i s protonated.
The anionic a-coraplex s a l t i s formed at high amine concentration.
At room temperature the alkoxide group i s l o s t t o give a picramide
derivative. R O w N H Q C H ) C H R
O N > / \ ^ N C L 2
V NOH
2
(1.52)
( i v ) With Other Nucleophiles
The sulphite ion adds to C-3 of 2,4,6,-trinitroanisole i n aqueous
DMSO giving the (1.53) adduct ' which has two resonances due to r i n g
protons at 8.4 p.p.m. and 6.1 p.p.m.
O C H
NO
H H
NO
(1.53)
- 30 -
While i n water a di-adduct (1.54) i s formed whose N.M.R. spectrum shows
a single band due to r i n g protons at 6.0 p.p.m.
OMe
2 ' d
N 0 2
(1.54) (1.55)
(1.55) (R = MeO, P(0)(0Me) 2 ) have been found t o form anionic -
complexes with trialkylphosphites and with d i a l k y l phosphites i n the
presence of EtgN. N.M.R. and U.V. spectral data confirm the 141
addition of the phosphite group meta to R .
3. Methods of Structure Determination f o r Meisenheimer Complexes
( i ) Nuclear Magnetic Resonance (N.M.R.) spectroscopy
This technique often gives very clear evidence f o r the structure
of Meisenheimer complexes. Chemical s h i f t s and spin-coupling resonance
constants give a large amount of information about complex structure, and nature of substituents on the benzene r i n g . N.M.R. has been
86 used successfully to d i s t i n g u i s h between isomers and t h e i r s t a b i l i t y .
Thus the addition of methoxide to 2,4,6-trinitroanisole i n DMSO gives
the C-3 adduct, followed by the more thermodynamically stable C-l
isomer (1.13) and (1.14). S i m i l a r l y the observation of d i - and t r i -36
adducts at high alkoxide concentrations was possible by N.M.R. (1.15). Generally nucleophilic addition t o nitroaromatic substrates 2 3 leads to change i n hybridization frcm sp ( i n substrate) t o sp ( i n adduct). Simply t h i s gives r i s e t o a change i n the chemical s h i f t .
- 31 -
The change i n shif t of other ring protons has been attributed to the
increased negative change i n the ring of the complex 1 1. A diminished
diamagnetic anisotropy resulting from ring current may also be important
Detection of hydrogen-bonding i s also possible by this technique.
The adduct formed from sodium thioethoxide and picramide (1.56) has 37
two bands for the non-equivalent amino protons, indicating hydrogen
bonding.
The values of spin-coupling may reveal ' information about relative
bond angles and stereochemistry of many Meisenheimer complexes. An
example (1.57)
\ N
H H
NQ
-H\
2 (1.56)
7 R
H 1
H
( R = N O ~ c O C H - . ) (1.57)
J 3,5 1.9-2 cps
J, 5,6 10.2 cps
J 1,6 4.4 - 5.0 cps
J, H-l.H =5.0 cps
JH-1,H ,8 = 10.0 cps
- 32 -
Although N.M.R. i s a strong i d e n t i f y i n g t o o l f o r Meisenheimer
complexes, i t has sane l i m i t a t i o n s , where i t cannot be used e f f e c t i v e l y .
The presence of free radicals broadens the bands and complicates the
spectra. The nature of the solvent used i n N.M.R, often DMSO, won't
allow, f o r example, the formation of 1:2 and 1:3 adducts. The use of
isotopes, especially hydrogen isotopes, was and i s s t i l l of great help
t o N.M.R. studies. 137
Flow N.M.R. spectroscopy enables measurements t o be made i n
the range of 50 ms - 5 min and thus covers a range of reaction times
previously inaccessible t o N.M.R. investigation. This technique provides
an excellent diagnostic t o o l f o r the i d e n t i f i c a t i o n of transient i n t e r
mediate species. The reactant solutions flow continuously through a
mixing chamber and through the transmitter-receiver c o i l s of the probe
where the spectrum of the flowing, chemically reacting system i s measured.
At a constant flow rate the s o l u t i o n w i l l have constant composition and
no change i n the spectrum i s observed. Kinetic measurements can be
repeated by varying the flow rate. An application of t h i s technique
was the i d e n t i f i c a t i o n of the products of 2,4,6-trinitrotoluene with
methoxide ion i n (87.5% DMSO - 12.5% methanol) (v/v) solvent mixture.
The reaction of equimolar quantities y i e l d s f i r s t the complex (1.19),
(R = Me) i n a very fast reaction ( t ^ 25 s) and the anion (1.18) i n a
second slower reaction. On doubling the base concentration i n the same
solvent mixture, the only species observed i s the dianion (1.58) which
i s r e l a t i v e l y stable.
C H
NO O N
H
N 0 2
3
(1.58)
- 33 -
( i i ) U.V. and V i s i b l e Spectroscopy (Electronic spectroscopy)
The strength of U.V/visible spectroscopy l i e s i n i t s a b i l i t y t o
measure the extent of multiple bond or aromatic conjugation w i t h i n
molecules. This has been a t t r i b u t e d t o t r a n s i t i o n s from highest occupied
M.O. to lowest unoccupied M.O. Sp e c i f i c a l l y , t r a n s i t i o n s i n the v i s i b l e 90
region are due to charge transfer between the r i n g and nitrogroups
Since e x t i n c t i o n c o e f f i c i e n t s are high, small concentrations are needed ,
f o r t h i s technique r e l a t i v e t o those needed i n N.M.R. The position of
absorption maxima and the molar e x t i n c t i o n c o e f f i c i e n t depend somewhat
on the solvent employed (besides, of course the nature of the sub-
s t r a t e ) ' ' . The 1:1 adducts of p i c r y l ethers w i t h alkoxides show
generally two absorptions i n the v i s i b l e r e g i o n ^ ' ^ . The 1:2 adduct has a single absorption band, where as the 1:3 adduct i s a colourless
92 species . Adducts of 2,4-dinitro-6-X-anisoles and 2,6-dinitro-
93 4-X-anisoles w i t h alkoxides give two bands i n the v i s i b l e region ,
the wave lengths varying w i t h the substrate. U.V/visible spectroscopy
i s less diagnostic i n giving s t r u c t u r a l information about Meisenheimer
complexes than i s N.M.R. spectroscopy. On the other hand i t i s very
useful i n determining equilibrium and rate constant associated with
complex formation.
The Benesi-Hildebrand equation i s one example of i t s applications. 94
Derivation o f Benesi-Hildebrand equation
Nu + P C
where Nu = nucleophile, P = Parent and C = complex. The equilibrium constant
[ C ] ( [ N u ] s t - [ C ] ) a p j s t - t q )
where st = stoichiometric concentration and where the two terms i n the
denominator represent the molar concentrations of free nucleophile
and free parent, respectively, and [ c j = molar concentration of the
- 34 -
complex.
I f [NU] » [c] -* [ Nu] - [ C] a [ Nu]
e . i g g i o ^ i )
(A form of the Beer-Lambert law)
where ec i s the molar e x t i n c t i o n c o e f f i c i e n t for the complex C at the
wavelength of absorption. From 1.12
[ c l K= L~t 1.14
Wst^Mst - f C ] > rearranging
[Cj - K ( [ P ] S - [C])[NuJ s t 1.15
. • . [ c ] = K ( [ p ] s t - - ^ Z i ) ) [ N u ] s t
• .• [c] - i o g d o / I ) 1-17 € c€ (from equation 1.13)
Equating 1.16 by 1.17, rearranging and d i v i d i n g both sides by e
1 1 [ P ] S T ^ + — = — 1.18
* ' K W s t 6 c 6 0 iogd 0/ 1) Io
p u t t i n g log - j — = O.D and I = 1
Substituting these values i n equation 1.18 1 1 1 [P] = _ St 1.19
K£ c [ N u ] s t €c 0.D
where [p] , i s the stoichometric concentration of parent. DP] st 1
So the slope (from equation 1.19) of • -Q- versus — p l o t gives
the thermodynamic equilibrium constant. Usually t h i s equation i s
- 35 -
applied when the ex t i n c t i o n c o e f f i c i e n t i s not known. Li n e a r i t y of
Benesi-Hildebrand p l o t s doesn't necessarily mean that only one coloured 140
species i s present
( i i i ) Crystallography
Crystallographic studies have confirmed the Meisenheimer complexes
structures obtained using N.M.R. and in f r a - r e d spectroscopy.
v X 2 \ A
C . M . 0 8 'C c / ' 1 V J l O O t J-A to
RO
C a a B a s a a a a £ a g E ^ r 1 RCL;
o
t
1.59
Crystallographic investigation has been carried f o r some p i c r y l ether 95 96
adducts ' . The main features from X-ray crystallographic, can be
summarised i n the following points (1.59).
* C4 - N2 bond i s shorter than C2 - Nl and C6 - N3 bonds which supports
the fact that a large proportion of negative charge i s localized on
oxygen atoms of the NCv, group para t o CI.
* The plane containing the two alkoxy groups i n perpendicular to the
aromatic plane.
- 36 -« The length (1.42°0 of the Cl-08 and CI-07 bonds i n the alkoxide groups
i s close t o that observed in a l i p h a t i c ethers and i s much greater than
that in 2,4,6-trinitrophenetole where delocalization of an oxygen ion
p a i r i n t o the aromatic r i n g occurs. * The C6 - CI - C2 bond angle i s 109°, very close to the tetrahedral
3 angle required f o r an sp — hybridization,
( i v ) Infra-red Spectroscopy
The i n f r a - r e d spectra of a-conplexes have been studied. Spectra
for p i c r y l ethers show bands t y p i c a l of ketals supporting the Meisenheimer
complex structure. The n i t r o group has c h a r a c t e r i s t i c strong absorption
frequencies, and can be distinguished i n the substrate- or complex 131-133
where they carry more negative charge . Analysis of i«,r spectra i s 103
not an easy matter. The d i f f i c u l t i e s are : overlapping of other
bands, overtones (harmonics) may s h i f t the frequency of the o r i g i n a l
band and a s h i f t w ith incorrect i d e n t i f i c a t i o n of the band may r e s u l t
from hydrogen-bonding, conjugation and other s t r u c t u r a l features.
Relative S t a b i l i t i e s of Meisenheimer Complexes
(A) Variation of nature of parent molecule
I t i s usually found that alkoxide addition at un-substituted
positions of ni t r o - a c t i v a t e d a r y l ethers i s k i n e t i c a l l y favoured but
that alkoxide addition t o the r i n g carbons carrying the alkoxy group
leads to a thermodynamically more stable adduct. One explanation f o r
t h i s e f f e c t i s i n terms of s t e r i c f a c t o r s ^ ' . In a l k y l picrate
parent molecules, the alkoxy groups are i n the r i n g plane, and rotations
up t o 61.3° have been observed f o r an ortho n i t r o group. The two
alkoxy groups i n 2,4,6-trinitro-l,1-dialkoxy benzene adduct are out of
the r i n g plane, thus r e l i e v i n g the s t e r i c s t r a i n implemented by the 95
flanking ortho n i t r o group . The n i t r o groups are planar with r i n g i n
the di-alkoxy picrate adduct.
- 37 -
TABLE 1.1
S t a b i l i t y of complexs with methoxide ions i n methanol at 25°C.
(Parent)
1.3.5- Trinitrobenzene
2,4-Dinitroanisole
2.4.6-Trinitroanisole
2,4-rDinitrobenzene
2,4^Dicyano-6-nitro anisole
2,6-Dicyano-4-nitro anisole
N,N-dimethyl picramide
Picramide
( 1 mol - 1s 1 ) ^forward
[1:1]
2.1 x 10
17.3
-3
2.0
34
(1 mol 1 ) Keq
15.4
5 x 10
17,000
5 x 10
10
12
7
38
-5
-7
[1:2] Keq (1 m o l - i )
1.3 x 19
CL:3] Keq - 1 , (1 mol )
10 -5
Ref
98
99
100
14
101
101
52
52
Steric factors w i l l be less important f o r alkoxide additions t o 1,3,5-
trinitrobenzene and 1,3-dinitrobenzene. Addition of an alkoxide ion
at C-3 i n activated anisoles i s k i n e t i c a l l y preferred r e l a t i v e t o
addition at C-l despite the fact that C-l complex i s less strained
than the parent compound. The t r a n s i t i o n state leading t o C-3 (1.61) 46
complex i s less strained than t r a n s i t i o n state leading to C-l (1.60).
C H O ,
(1.60)
Transition State leading to C-l adduct formation.
C H O ,
O C H -
(1-61) Transition State leading to C-3 adduct formation.
- 38 -
The higher s t a b i l i t y of the 1:1 t r i n i t r o a n i s o l e complexes i s due t o
release of s t e r i c s t r a i n i n the parent and to the inductive e f f e c t
of the methoxy group.
The s t a b i l i s a t i o n of sp hybridised carbon atoms by mul t i p l e
alkoxy s u b s t i t u t i o n may also be an important factor.
The ground-state resonance s t a b i l i s a t i o n f o r the parent 2,4,6-
t r i n i t r o a n i s o l e can be represented by: (equation 1.20).
O C H O C H
NO O N N O 0_N
NO N O
.... 1.20
The 1,3-complex can also benefit from resonance s t a b i l i s a t i o n involving
the methoxy groups as shown i n equation 1.21.
O C H O C H
NO O N
O C H 1.21 H
N O NO
However addition at C-l results i n the loss of such resonance s t a b i l i
sation. This w i l l tend to reduce the rate of 1,1-complex formation com
pared to the rate of 1,3-complex formation from t r i n i t r o a n i s o l e and
also r e l a t i v e to alkoxide addition to trinitrobenzene . The data
in the Table 1.1 demonstrates the importance of the
- 39 -
presence of a strong electron withdrawing group para to the position
of addition also i n s t a b i l i s i n g Meisenheimer complexes. The more 32
the r i n g current i s delocalized the more stable i s the complex
Measuring the s t a b i l i t i e s of di-adducts (propenide complexes) i s not an
easy task due to the high concentrations of nucleophile usually
required. Such equilibrium constants are strongly dependent on i o n i c
strength, so extrapolation t o i n f i n i t e d i l u t i o n i s necessary i n t h i s
case. The s t a b i l i t y of di-adducts formed from 1-substituted 2,4,6-
trinitrobenzenes increases with increasing size of the 1-substituent
(1.62 - 1.65). This may be a t t r i b u t e d to the increasing release of s t e r i c compression between the 1-substituent and the two ortho n i t r o
32 groups .
O C H , HC
N0_ OM&''-^ K2
H H
N Q . so" as
3 3
NC^ O N ^ f ^ i N O O N
,H ^ 2 H N , H N H.
NO, ^ o 3 s
N O . sc>o3s<
(1.62) (1.63) (1.64) (1.65)
Increase of s t a b i l i t y
(B) Variation with attacking nucleophile
Defi n i t i o n s of some terms r e l a t i n g t o t h i s subject are given
below.
( i ) Carbon bas i c i t y * ^ '
Is a measure of the thermodynamic a f f i n i t y of nucleophiles f o r an
aromatic carbon atom i n the parent molecule.
- 40 -
( i i ) Bronsted basicity Is a measure of the thermodynamic a f f i n i t y of nucleophiles for
protons. Accordingly, the values of the equilibrium constants i n the table
1.2 give a measure of the carbon basicities of the nucleophiles. TABLE 1.2
Equilibrium constants for formation of adducts from 1,3,5-Trinitrobenzene with various nucleophiles.
Nucleophile QMe~ SEt" SPh" OPh" OMe SPh"
The order of carbon basicity i n methanol i s : EtS" > 0Me"> PhS~> PhO"
While the order of Bronsted basicity i s 0Me"> EtS~> Ph0~> PhS"
These quantities depend on the nature of the solvent. The mode of interaction may depend on the nature of the nucleophile. Thermo-dynamically, stable adducts of 2,4,6-trinitroanisole are formed with OMe-, N 3 or NEtg" by addition at C-l. While, with the same substrate, addition at the unsubstituted carbon C-3 i s observed with nucleophiles such as SO or CH„.C0.CH~ This may be attributed to steric strain associated with having two bulky groups attached to the same carbon atom 1 1. Another example is the ionization of the activated N-substituted picramides. Sulphur bases l i k e SEt - or SPh- form addition complexes at
37 unsubstituted ring carbon
Solvent K, ( 1 mol - 1) Ref. Me thanol 1.54 x 101 98 Me thanol 3.50 x 10 3 37 Methanol 1.95 37 Methanol < 2 x 10~3 37 D.M.S.O. <-> 10 9 37 D.M.S.O. 8 x 10 4 37
- 41 -
While alkoxides (OMe~) abstract an amino proton or add to un-55
substituted ring carbon . (C) Solvent Effect:
103 Defining seme terms in connection with this subject. Dipolar Aprotic So^vents^ Polar solvents of moderately high di-electric constants, which
don't contain acidic hydrogen, such as D.M.S.O. and sulfolane. These solvents are able to dissolve ionic compounds, by solvating cations most strongly, and leaving anions relatively un-encumbered and highly reactive.
Protic_Solvents: Are acidic due to the hydrogen attached to oxygen or nitrogen, such
as water and alcohols. Through hydrogen-bonding such solvents tend to solvate anions particularly strongly, thus reducing their nucleophilic power.
Accordingly, solvents may have large effects on the s t a b i l i t y of Meisenheimer complexes. Generally cations, polar molecules, and large polarisable anions such as a-adducts, are better solvated by dipolar aprotic solvents than by protic solvents. In protic solvents only small anions (strong hydrogen-bond acceptors) are well solvated. Hence equilibrium constants for a-adduct formatin are generally enhanced on transfer from protic to dipolar aprotic solvents.
TABLE 1.31
Interaction of 2,6-Dicyano-4-nitroanisole with Sodium methoxide in D.M.S.O-methanol solvent.
DMSO, M K, 1 mole' -1
0 33.5 1.41 77.0 2.82 221 4.23 695
- 42 -
I t i s found that on increasing the amount of DMSO in the solvent there i s an increase i n value for the rate constant ( k , ) " ^ for the formation of the complex: sodium-l,l-dimethoxy-2,4-dicyaiio-6-nitro cyclohexadienate, and a decrease in complex decomposition rate constant (k Desolvation of the methoxide ion as D.M.S.O. concentration i s increased leads to an increase i n k^. The formed Meisenheimer complex (highly polarisable) i s well solvated by D.M.S.O., leading to a
46 decrease i n k ^ value. I t has been noticed that the formation of 1,1-adduct (from sodium methoxide and 2,4,6-trinitroanisole) i s catalysed by increasing the concentration of methanol and methoxide. Meanwhile increasing D.M.S.O. concentration stabilises the i n i t i a l C-3 adduct. In early s e v e n t i e s ^ 5 - ' ^ the change in enthalpy was measured for the reaction of 2,4,6-trinitroanisole with sodium methoxide. The heat of formation of the 1,1 adduct, formed from 1,3,5-trinitrobenzene and sodium thiophenoxide (CgHj-S~Na+) has also been measured in solvent mixtures of D.M.S.O. and methanol. The enthalpy of transfer for sodium methoxide from pure methanol to 95% DMSO - 5% methanol (v/v) solvent mixture i s equal to&H 10 kcal/mole, while for sodium thiophenoxide i n the same system, the enthalpy change i s equal to AH 0.94 kcal/mole. The values of^H for transfer of the adducts formed are similar and have values of ca - 7 kcal/mole - 1.
From previous s t u d i e s * ^ ' i t has been argued that the s t a b i l i sation of the methoxide ion due to hydrogen-bonding decreases as the amount of D.M.S.O. increases. However the Meisenheimer complex i s stabilised much more in D.M.S.O. than i s the parent, and the heat of transfer of the adduct from methanol to D.M.S.O. becomes more exothermic as D.M.S.O. concentration increases. The observed negative entropy arises from the increased solvation of the complex corresponding to
- 43 -
the starting materials. (An entropy loss w i l l arise because of a decrease i n the number of species from two reactants to one adduct and/or from increased solvation of the adduct). From this study in which ion-pairing i s of low importance, enthalpies and entropies for complex formation become more negative as the alcohol becomes less polar.
108 A study for the reaction of 1,3,5-trinitrobenzene with cyanide
ion in different alcoholic solvents revealed smaller value for K in methanol (40 1/mole) compared with that i n t-butanol (5 x 10 1/mole). Enthalpy changes vary from zero i n methanol to -15.5 k cal/mole - 1 i n t-butanol, while entropy changes decreases from +7 in methanol to -26 cal deg - 1 mole-"1" i n t-butanol. This has been attributed to the desolvation of cyanide ion, as t-butanol solvates the cyanide ion to a limited extent. In contrast methanol i s a good solvating solvent for
109 the small cyanide ions. In alcohol-water mixtures a rapid e q u i l i brium between hydroxide and alkoxide ions i s reached according to the chemical equation 1.22.
0H~ + ROH ± R0~ + H20 1.22 Generally, such equilibrium studies have been neglected, one of the main reasons was that the reactivity of hydroxide ion with many substrates are low compared with some alkoxide ions. Although, according to the present work the presence of traces of water in some alcohols has a large effect on the kinetics of some a-complex forming reactions.
Danil de Namur"^0 found that the free energy of simple cations and anions increases along the series of the following alcohols:
MeOH< Et0H< 1-PrOH (D) Acidity Functions
The breakdown of the pH scale as a useful measure of acidity for solutions whose ionic strength i s greater than 0.1 m leads to the
- 44 -
necessity for some other quantitative scale which expresses the acidity of more concentrated solutions. Taking this into consideration,
113 Hanraett and Deyrup suggested i n 1932 a scale using spectrophotometric techniques, to measure the a b i l i t y of the acid solution to protonate a neutral solute species (or indicator). The equilibrium is of type equation 1.23.
B + H+ BH+ 1.23 The acidity function was defined by equation 1.24
[BH +3 Ho = p K b h + - l o g 1 0 — 1 2 4
where pKgjj+ i s the acid dissociation constant for BH+ (conjugate acid of B) and Sr—- i s the concentration ratio for the indicator after and [BJ before the protonation. Spectrophotometry provides a dependable means for the determination of the indicator ionisation ratios and the conjugate base dissociation constant. The evaluation of pKgjj+ follows directly from knowledge of ( ) as a function of acid concentration as
B described in the equation 1.25
^ 0*3 f B H + 1
At i n f i n i t e dilution, a l l a c t i v i t y coefficients tend to unity giving
equation 1.26
% + = Io%o (CfgJ ) " l o*10 ^ ^ 2 6
The knowledge of pKgjj+ provides the correct thermodynamic dissociation constant referred to pure solvent as standard state.
The H_ acidity function measures the a b i l i t y of the strongly basic solution to abstract a proton from the weakly acidic neutral solute
114 11 •=> SH, and is defined \jyXJ-*' x equation 1.27 and 1.28
- 45 -
SH + OH ;=i S + H O 1.27
H = pK<, + log £l2 1.28 ^ H 1 0 tad
The measurement of an H scale involves the determination of pKgjj and the variation of log with increasing hydroxide ion concentration for a weakly acidic neutral indicator SH. The ratio ([S -]/[SH]) i s measured by electronic absorption spectrophotometry, a method which i s used under two conditions. The neutral acid SH and i t s conjugate base S~ must have measurably different absorption spectra, and the extinction coefficient of either SH or S~ at the selected wavelength of study must be such that the concentration of indicator necessary for measurable absorption changes has negligible effect on the overall acidity of the medium. One of two methods to determine are followed; the f i r s t i s an extrapolation of, Io§io[^3~ IOS^QLMOH] versus MOH , to zero concentration of M3H, giving a value for the
114 \s~1 intercept of pKw - pKg^ . The ionization r a t i o can be found by the relation equation 1.29
PI = D - DSH 1.29
[SH] Dg- - D
From a series of base concentrations for a fixed SH, Dg^ i s the optical density i n dilute base solution, Dg- i s the optical density at very concentrated base solution and D refers to some intermediate acidity. Here the presence of isobestic points i s a good test for the r e l i a b i l i t y
TS"! for the direct calculation of the ratio L_J t
[SH] 116
I t has been found that more acidic indicators give linear plots of l°g-LO[|jij ~ log Q MDH] versus [MQHJ , where less acidic indicators give curved plots, because of shifts i n wave lengths due to medium effects. In the l a t t e r case, the second method of stepwise comparison,
117 118 should be used. This method ' i s simply the mean of ionization ratios
- 46 -
at n studied wavelengths and i s given by the equation 1.30
[ S i = I Y ( ? ^ H \ [SH] n j=nTn \ DS - D/Aj
The H j acidity function for methanol i s defined by the equation 1.31
' + 1 O g10 M SH 1 U [SHJ % = pIC! + l o gio H ^ M
where pKgjj i s the dissociation constant of indicator SH in methanol. 70
Because of the low dielectric constants of the alcohols ion-association i s important even at low concentrations of base. Not surprisingly therefore the trend i n basicity as a function of the metal cation i s more pronounced than i n water-hydroxide media although the order i s :
HM(KCMe)> HM(NaOMe)> H^LiOMe) The J_ acidity function i s defined by the equation 1.32 and 1.33
R + OH"^ ROH~ 1.32 , , JROH \ J = pKK + lo g ^ f L " " " J1 1.33 — w
in which K i s the equilibrium constant for the addition of OH ions to 117 119
an electrically neutral indicator molecule R ' 120
Rochester defined a acidity function for methanolic sodium methoxide referring to pure methanol as standard state as equations 1.34 and 1.35.
R + OMe~ =; ROMe" 1.34 T sirrs N . T [ROMeJ „ or-JM = P^eOH^ + 1 O g l 0 ^ j ^ j - i - 3 5
where pKjjgQjj i - s "the autoprotolysis constant for methanol and K i s the thermodynamic equilibrium constant for methoxide addition to the neutral
- 47 -
indicator species R. Similar treatment for J M as in case of H are usually followed.
121 Crampton et a l . measured J M acidity function for methanol - D.M.S.O.
mixtures using nitro-activated anisoles as indicators. They used the concept of acidity function to calculate the thermodynamic equilibrium constant (K^) for sodium methoxide addition in methanol to some X-substituted dinitroanisoles to form Meisenheimer complexes as given in the equation 1.36
[parentj (where pK,^ = 16.92) 1 1 6
- 48 -
ION-ASSOCIATION
! T„+^,,„+-; ™,122,123 Introduction Twenty years ago ion pairs were not thought to be an important
factor in reaction kinetics, now no detailed mechanism is drawn up without recognising ion association. The Bronsted-Bjerrum equation:
l o g 1 Q k = log k Q + 2ZAZgA 1.37 " AB [where k i s the rate at i n f i n i t e dilution (k = k — — ) . z A and ZL O O „ A ti fc
are the charges of reacting species A and B. For water as solvent A = O.509 mol 2 dm 2 at 25 c, and y is the ionic strength of the medium] is not always successful due to ion-association.
For instance a centrally charged sphere w i l l be an unsatisfactory model for a large organic ion with more than one polar group. Ion-association can affect reaction kinetics i n a variety of ways, i t w i l l lead to a reduction of the ionic strength, i f reactants are involved, drastic influences on the rate w i l l be observed, further the associated ion may influence the reactivity of the reacting species. Ion-pairing w i l l be mostly important when the dielectric; constant of the medium i s low, when ions have high charge, and i f ions are present at high concentration . Because of the low dielectric constants of alcohols relative to water, ion association would be expected to play a more important part i n reaction kinetics investigation in these media.
120 124 Acidity function measurements ' of concentrated alkoxide solutions show that for a given concentration:
^(KDMe^ i y NaOMe)>^(LiOMe) this order being the same as for the corresponding hydroxide and attributable to ion association.
- 49 -
2. Ion-pairing relation with rate constants 125
Crampton and Khan have suggested that the variation of equilibrium constant with alkoxide concentration, for a-complex formation, i s partly due to ion-association, and that this i s more marked between the cation and the anion "Meisenheimer adduct" than between the cation
126 and alkoxide ion. Crampton proposed a model (Scheme 1.11) accounting the effect of ion-pairing in formation of Meisenheimer adducts equation 1.38.
P + OR + M P. Of M
CR-
P + M . OR k. ip k. lp
^ ^KP.OR"
P.OR , M
M = metal cation (univalent). P = Parent molecule. OR" = Alkoxide anion.
Scheme 1.11
[P.0R"3 + [P.0R-,M+] 1 gg Kc = [P] ([0R~] +[M +,0R"])
The act i v i t y coefficients have been implemented in this model in the following way: assuming [OR-] .> [ p - < - ) R _ ] t o t a l ' degree of dis-association of metal alkoxide ion pairs i s evaluated by equation 1.39.
( 1 - °C)
- 50 -
where y i s the mean acti v i t y coefficient for free ions and i s related to the overall concentration of alkoxide by a modified Debye-Huckel equat ion,equat ion 1.40
H>1stoich>° - l o g y - x 1.40 1 + Bq(e,[0R-]
2 where q = (Bjerrum c r i t i c a l distance).
2DkT
(A and B are Debye-Huckel parameters).
—1 3 - 1 127 (A = 2.319, B = 5.907 mol dm nm and q = 1.153 nm for ethanol system). The two unknowns <xand y were evaluated from equations 1.39 and 1.40, by iteration. Inserting the a c t i v i t y coefficients in equation 1.38 we obtain equation 1.41
K(l +[M +]y JV P.0R- )
K = ' 1.41 ° 1 + [ M > 2 K M + , O R -
where K = — (scheme 1.11). k-
The variations with metal ion concentration with the forward, k f, and reverse, k , rate coefficients are given by equations 1.42 and 1.43
k f = koc+ k i p (l-*0 1.42 k_ + [ M 4 ] y 2 k - i p i { M 4 p Q R -
k = — — — 1.43 r
where k , = k.rMORl . . . + k 1.44 obs fL J stoich r 3. Importance of ion association
Crampton and Khan found that addition of sodium salts caused an increase i n value of the equilibrium constant, K , indicating that
- 51 -
KM+ FP.aR-> KM+,CR- (seeschemel.il) They found that association constants of Meisenheimer complexes (formed from 2,4,6-trisubstituted anisoles with some metal methoxies, barium
126 and calcium salts) with cations decrease in the order:
„ 2+ „ 2+ „ + T,+ T .+ Ba > Ca ^ > Na N K > Li Lithium ions have l i t t l e tendency to associate with the studied Meisenheimer complexes due to their strong solvation. Speculating about the structure of the ion associates produced we have the following possibilities:
where metal ion associates strongly with the nitro group (1.66). Similar association occurs when other electronegative substituent such as CCX Me, at the positions para-ortho to addition.
The small tendency of 1,3,5-trinitrobenzene adduct to associate relative to the anisole adduct has been explained by the cage effect, where the cation is being held by the oxygen atoms around the position of addition. The ortho - CO Me group provides better stabilisation than ortho - NO group (1.67) and (1.68).
M e O ^ O M e X
V N
O o M
(1.66)
- 52 -
M
O >o OMe O
Y Y (1.67) (1.68)
125 128
I t has been found ' that the methoxide adduct of 1,3,5-trinitro-benzene and also spiro-Meisenheimer complexes show no evidence for association with cations i n methanol. The interaction thus appears to
129 be specific to 1,1-dimethoxy-complexes .
As shown in (1.69) four oxygen atoms are available for complexing Na +
O O N N o o Y
(1.69)
Buncel and co-workers have compared the efficiencies of free anions and of ion-pairs i n a -complex forming reactions and i n proton-transfer reactions (e.g. 2,4,6-trinitrotoluene). The ion-pair may be more effective in cr-complex formation than i n proton transfer. For instance in the case of T.N.T. which i s described by (1.70) and (1.71).
- 53 -
Na NO. J
6-membered structure ' (1.70)
P H-O
8-membered structure (1.71)
Here, a six-membered cyclic transition state should be much more favourable than the eight-membered structure. The dependence of the equilibrium constant for formation of a Meisenheimer adduct on base concentration has been interpreted in terms of ion-pairing effects.
12(3 127 In the previous ' and present work, the 1:2 complexes appears to undergo specific ion pairing effects with cations, What made ion-association an important effect i s the nature of the solvent especially when they have low dielectric constants.
130 Recent kinetic study of the reaction of 4-nitrobenzenefuroxan
with isopropoxide ion in isopropanol showed that plots of k^^, for a-complex formation, versus (i_PrO~) are linear indicating surprisingly that ion-pairing effects are not a problem at the concentrations of base employed in these studies.
CHAPTER 2
EXPERIMENTAL
I Solvents
water:
n-propanol:
t-butanol:
D i s t i l l e d water was boiled to remove carbon dioxide and subsequently protected from the atmosphere with soda lime guard tube. A.R propanol (n-propyl alcohol) was used without purification. A.R methyl isopropyl alcohol was used either as
143 144 supplied or was dried over ' potassium or molecular sieve and fractionated, or was dried by
145 fractional recrystallisation . The dried alcohol was stored in a desicator containing s i l i c a gel. A.R methanol was used without purification. A purified solvent was available, thanks to Dr. B. Gibson. The commercial solvent was dried with calcium hydride and fractionated under reduced pressure. The middle fraction was collected and stored in a desicator containing s i l i c a gel.
I I Solution of bases :
methanol: Dimethyl-sulphoxide:
sodium hydroxide:
Potassium hydroxide:
Standard solutions of Analar sodium hydroxide were used after checking the concentration by t i t r a t i o n with Standard hydrochloric acid. Standard solution of Potassium hydroxide were used after t i t r a t i o n with standard hydrochloric acid.
- 55 -
Tetra methyl ammonium n-propoxide:
Tetramethyl ammonium t -butoxide:
Tetra ethyl arrmonium t -butoxide:
sodium propoxide:
sodium t -butoxide:
potassium t -butoxide:
Was prepared by diultion of concentrated tetra-methylanmonium hydroxide i n water with n-propanol. The solution was then t i t r a t e d with standard hydrochloric acid. This prepared solution contained small concentrations of water. In very dilute solutions no unwanted effects were observed from this source although in solutions containing 0.02 mol l - 1 base where 0.8% water is present
a slow side reaction giving the corresponding phenol was observed, notably i n the reaction of l-propoxy-2, 4-dinitro-6-propoxy carbonyl benzene. Was prepared by diluting the concentrated tetra-methylammonium hydroxide i n water with t-butanol. The tetramethyl ammonium hydroxide i s less soluble in t-butanol than i n n-propanol. The diluted solution was t i t r a t e d with standard hydrochlocic acid. Was prepared by diluting concentrated tetra ethyl anmonium hydroxide in water with t-butanol. The prepared solution was t i t r a t e d with standard hydrochloric acid. Was prepared by dissolving clean sodium in Analar n-propanol under nitrogen and was t i t r a t e d with standard hydrochloric acid. Clean sodium was dissolved i n warm Analar t -butanol. The base was then t i t r a t e d with standard hydrochloric acid and stored in a warm place. Clean potassium was dissolved in warm Analar t -butanol, then t i t r a t e d with standard acid and stored in a warm place.
- 56 -
sodium methoxide: Was prepared by dissolving clean sodium metal
i n Analar methanol i n a nitrogen atmosphere. The
cloudy solution was centrifuged u n t i l a clear
solution was obtained. The base was t i t r a t e d
w ith standard sulphuric acid.
Potassium methoxide; The freshly cut pieces of potassium metal were
dissolved i n Analar methanol under nitrogen. The
cloudy, solutions were centrifuged and t i t r a t e d
w ith standard sulphuric acid.
Lithium methoxide: The freshly cut pieces of l i t h i u m metal washed
then dissolved i n a warm Analar methanol. The
cloudy solutions were centrifuged and t i t r a t e d
with standard sulphuric acid,
used to maintain constant i o n i c strength. I l l Salts :
sodium t e t r a -phenyl boron:
Sodium perchlorate:
IV N i t r o compounds
1,3,5-Trinitro-benzene:
l-propoxy-2,4-dinitro 6-chlorobenzene:
A dried A.R grade reagent from BDH.
A.R grade reagent which was dried under vacuum
before use.
A r e c r y s t a l l i s e d commercial 1,3,5-Trinitrobenzene
was available and was used without further 150
p u r i f i c a t i o n (m.p 122°C, l i t m.p 122.5°C).
The preparation was started with 1,2-dichloro-
4,6-dinitrobenzene (m.p 56°C) which was prepared 146
by Dr. H. Khan following the method of Ullman 147
and Sane , by chlorinating 2-chloro-4,6-
dinitrophenol 3.5 grams of 1,2-dichloro-4,6-
dinitrobenzene was dissolved i n a hot n-propanol
- 57 -
and one equivalent of soidutn propoxide was added wit h s t i r r i n g . The reaction mixture was heated on a water bath for two hours, allowed to cool then a c i d i f i e d with d i l u t e hydrochloric acid, when the required ether separated as a pale "brown" o i l . This was separated and s o l i d i f i e d by addition of s o l i d C02 (dry i c e ) , then r e - c r y s t a l l i s e d from n-propanol t o give yellow crystals (mp. 40°C). ^H.n.m.r confirmed the product's structure. Equations describe t h i s reaction as follows:
CI 0 C O N v V
NO
O N NaOPr NaCL
NO
- 58 -
l-propoxy-2,4- 10.1 grams of l-chloro-2,4-dinitrobenzene d i n l t r o benzene: 1 4 R
(m.p 53 C, l i t m.p 53°C) were dissolved i n the least amount of n-propanol with heating 50°C).
After the halobenzene had dissolved, one equivalent
of sodium propoxide was slowly added. A deep
brown colour was formed. After t h i s addition the
mixture was heated f o r about 30 minutes (during
which the solution became transparent). The
fla s k was allowed to cool. An excess amount of
d i s t i l l e d water was added, followed by a c i d i f i c a t i o n
w i t h a small amount of IC1. The required product
appeared as o i l y drops, which were separated.
C r y s t a l l i s a t i o n from n-propanol gave a product o 14Q o
with (m.p 31 C, l i t : rn.p 30.7 - 31.2 C).
^H.n.m.r showed band consistent w i t h the required
compound and indicated the absence of impurities.
This preparation i s described by the equation:
NaOPr.
O P r
NaCl
- 59 -
l-propoxy-2,4-
dinitro-6-propoxy
carbonyl benzene:
O P r 0 X N - C Q P r O N
NO
Was prepared from 2-chlorobenzoic acid i n three
stages:
(a) 41 grams of 2-chlorobenzoic acid and 198
mis of cone, sulphuric acid (d = 1.84) were placed
i n a two l i t r e round bottomed flask and warmed
on a heating mantle w i t h mechanical s t i r r i n g , u n t i l
the benzoic acid dissolved. 66 mis of fuming
n i t r i c acid was added with s t i r r i n g and the
mixture was allowed t o stand f o r an hour. (The
sulphuric acid and fuming n i t r i c acid were both
added slowly). A s o l i d mass accumulated on the
surface. The mixture was heated at 90° - 100°C
for three hours, allowed to cool down and 50 mis
of more fuming n i t r i c acid (sp. gr 1.54) was
added with s t i r r i n g and the reaction mixture was
then heated at 100 - 110°C f o r a further three
hours. ( I t i s important to keep the temperature
i n the range mentioned above, taking i n t o account
that t h i s reaction process i s an exothermic one).
The mixture was allowed to stand overnight and was
then poured onto crushed ice. The r e s u l t i n g s o l i d
- 60 -
was f i l t e r e d o f f and pimped, washed with d i s t i l l e d water and dried (m.p 199°C, l i t 1 5 0 m . p 199°) giving white c r y s t a l s .
(b) 42 grams from the r e s u l t i n g 3,5-Dinitro-2-
chlorobenzoic acid was dissolved i n 325 mis of
warm n-propanol and 23 mis of cone, sulphuric
acid "d = 1.84" was added.
The mixture was then heated on a water bath f o r an
hour and then allowed to cool, when the propyl
ester of the acid separated as a c r y s t a l l i n e s o l i d .
This was f i l t e r e d and washed with aqueous sodium
bicarbonate then water, and r e c r y s t a l l i s e d from
n-propanol (m.p : 45 - 46°C).
(c) The propyl ester of 2-chloro-3,5-dinitrobenzoic
acid obtained above was subjected to nucleophilic
replacement of chlorine by reaction with one
equivalent of sodium propoxide, and the r e s u l t i n g
compound was c r y s t a l l i s e d from n-propanol
(m.p 38°C).
The ^H.n.m.r sepectra showed bands consistent with
the required compounds indicating the absence of
impurities.
I t i s of interest to mention that a l i t e r a t u r e
search indicated that the f i n a l product had not
been previously prepared.
l-propoxy-2.4.6-trinitrobenzene: Was prepared by reaction of p i c r y l chloride w i t h
sodium propoxide.
- 61 -
CI OPr 0 VrNO O N O N + NaOPr + NaCI
NO NO
Picrylchloride:
P i c r i c acid:
2,4-dinitrophenol:
13.1 grams of p i c r y l chloride was dissolved i n the
least amount of n-propanol with heating (50°C).
After a l l the p i c r y l chloride had dissolved, 66 mis
of (0.805 M) sodium propoxide was slowly added. A
dark colour formed. The mixture was heated f o r 3
half an hour then cooled down. A 20 cm portion of 3
t h i s solution was added to 100 cm of d i s t i l l e d
water, and a white precipetate auickly formed. An
excess of d i s t i l l e d water was added to the main bulk
of the solution followed by a c i d i f i c a t i o n with
small amount of HC1. The product separated as an
o i l which was c r y s t a l l i s e d from n-propanol. The
f i n a l product had (m.p 41°C, lit:443°C).
Recrystallised commercial specimen (m.p 82°C,
lii4® m.p 83°C).
Recrystallised comnercial specimen (m.p 122°C, 148 o l i t : m.p 122 - 123 C).
Recrystallised commercial specimen (m.p 113°C, 148
l i t : m.p 115 - 116°C). o. 1,3-dinitrobenzene: Recrystallised conmercial specimen (m.p 90 C,
148 l i t : m.p 90.02).
62 -
l-chloro-2,4-dinitro- Recrystallised conmercial specimen (m.p 50°C, benzene:
L i t :148m.p 53°C) 146
6-methoxy-2,5- Recrystallised sample prepared i n previous work d i n i t r o benzoic acid: 150
(m.p 110°C, l i t : m.p 112°C). 2,4,6-Trinitro- Recrystallised sample prepared by Dr. M.A. E l -anisole:
Ghariani (m.p 77°C, l i t : m.p 68°C) 0
152 2,4,6-Trinitro- Recrystallised sample prepared i n previous work a n i l i n e : 150 (picramide) (m.p 195°C, l i t : m.p 192 - 195°C).
152 N,N-dimethyl p i c r a - Recrystallised sample prepared i n previous work mide: 150
(m.p 139°C, l i t : m.p 138°C). 153
l-(2-Hydroxy Pale yellow c r y s t a l l s prepared by Dr. M.J. Wilson
S S ^ B : ( m.p62°C, l i t : ^ 6 1 ° C ) . 152
N-methyl pi c r a - Recrystallised sample prepared i n previous work . mide:
(m.p 116°C, l i t : 1 5 0115°C).
V Spectroscopic measurements :
V i s i b l e spectra
Optical density measurements, for use i n the measurements of rates
of slow reactions or f o r determination of equilibrium constants, were
measured on an SP500 spectrophotometer using matched s i l i c a c e l l s of
10 mm path length. The temperature i n the c e l l s was maintained constant
at 25°C by c i r c u l a t i n g water from a constant temperature bath through
a specially designed c e l l holder i n the spectrophotometer. The
recording instruments, Unicam SP8000, Beckman S25 and Pye-Unicam
SP8-100 were used at 30 ± 1°C. The technique usually used was to
allow the solvent containing base to come t o thermal equilibrium i n the
c e l l compartment before adding the parent solution.
The stock solutions were made up immediately before taking
measurements. In some cases complete conversion of the parent substrate
- 63 -
to complex could be achieved i n the basic media used. In these cases
the e x t i n c t i o n c o e f f i c i e n t e M of the complex could be found d i r e c t l y
by using Beer's Law:
I Optical density = l o g 1 Q ~ = e
M > C M . l
where i s the complex concentration, which could be determined i n less
basic solutions. Otherwise theBenesi-Hildbrand expression was used as
discussed i n the previous chapter. Kinetic measurements for fast
rates at 25+ 0.1°C (30 ± 0.5°C for t-butanol solutions) were made w i t h
a Canterbury stopped-flow spectrophotometer. The rate constants of
f i r s t order reactions, where [base] > [substratej , were calculated by
standard methods and were reproducible w i t h i n 5%.
Proton magnetic resonance spectroscopy :
"'"H.n.m.r spectra were measured wi t h a Bruker 90 MHz (HX 90E)
instrument. Measurements were usually made at ambient probe
temperature (25 ± 1°C). Tetramethylsilane (TMS) was used as an
int e r n a l reference. DMSO or DMSO-d„ were used as solvents with the b
alcoholic a l k a l i solutions i n the n.m.r. tube. Stopped-flow spectroscopy :
The "Canterbury" instrument was developed by Caldin and co-155
workers
Monochromatic l i g h t from a high i n t e n s i t y grating monocliromator
was directed i n t o s i l i c a measuring c e l l (2 rim. path length) by means of
a f l e x i b l e s i l i c a l i g h t guide and from there to a photomultiplier. The
signal from the photomultiplier was fed to a Tektronix 5103ND11 single-
beam storage oscilloscope.
The two reactant solutions are taken from reservoirs i n t o 2 ml.
d r i v i n g syringes which are connected t o a thermostated c o i l s and mixing
- 64 -
chamber. Activating the syringes (pneumatically or manually) causes
mixing of reactants i n the chamber and t h e i r passage i n t o the l i g h t
path, a f t e r t h i s the flow i s abruptly stopped by a stopping syringe.
At the same time the reaction i s followed spectrophotcmetrically by
t r i g g e r i n g the oscilloscope time-base switch. For a k i n e t i c run a
suitable time-base was chosen so that ^ 97% of the reaction could be
followed on the f i r s t trace. The oscilloscope was then triggered by
depressing the "automatic t r i g g e r " button t o obtain an " i n f i n i t y "
scale reading. Where a r e l i a b l e " i n f i n i t y " reading could not be obtained
owing to secondary reactions, rate constants were calculated by Guggen
heim's method*5^.
CHAPTER 3
KINETIC AND EQUILIBRIUM DATA FOR THE REACTIONS
OF SOME AROMATIC COMPOUNDS WITH PROPOXIDE IONS
IN PRCPAN-l-ol
I Introduction :
In t h i s chapter, rate and qui l i b r i u m data are given f o r the
formation of a-adducts by the reaction of propoxide ions i n propan-l-ol
w i t h 1,3,5-trinitrobenzene and a series of l-propoxy-2,4-dinitro-6-x-
benzenes (x = N0 2 > CI, C02Pr, H).
In previous work, k i n e t i c and equilibrium data have been presented 11 32
for the formation of a-complexes ' from various aromatic n i t r o
compounds with methoxide ions i n methanol or ethoxide ions i n ethanol 1 3' 152 -or isopropoxide ions i n propan-2-ol. Alkoxide (OR ) addition may
occur at un-substituted r i n g positions t o give complexes such as (3.1)
or (3.2) or at an alkoxy-substituted position t o give (3.3).
K . O R OR R O v / O R
O.N NO NO NO i
H R O • »
NO NO
(3.1) ( 3 . 2 ) ( 3 . 3 )
An important conclusion from previous work i s that the 1,1-
dialkoxy complexes (3.3) associate strongly with cations such as Na+, + 2+ 2+ K , Ba and Ca . Evidence f o r the association with cations of the
complex (3.3, x = H, R= Et) formed from 2,4-dinitrophenetole and 127 ethoxide has also been presented independently by Gold and Toullec
- 66 -
We have also shown that i n general free alkoxide ions and metal-
alkoxide pairs have d i f f e r e n t r e a c t i v i t i e s i n these systems. 33
Previously Gan and Norris have measured the rate of reaction
of sodium propoxide with 1,3,5-trinitrobenzene and found no evidence
of ion-association. The aims of the present work were to compare
rate and equilibrium data f o r prop-l-oxide additions with ttose f o r
other alkoxides and t o examine the e f f e c t s of ion-association in
these reactions. We have also compared the r e a c t i v i t i e s of free
propoxide ions and sodium propoxide ion pairs i n the nucleophilic sub
s t i t u t i o n reaction of 2,4-dinitrochlorobenzene.
I I Experimental : Sodium perchlorate s a l t (NaClO^) i s less soluble i n propanol
-1 -3 (2.97 x 10 moldm ) compared with sodium tetraphenyl boron (NaBPh^)
(8.42 x 1 0 - 1 mol dm-^) at 25°C. The ion-pair association constant, K ,
for NaClO^ i s 240 compared with 1 f o r NaBPh4, so that sodium t e t r a -
phenylboron has been used rather than sodium perchlorate**^.
I t was not possible t o carry out measurements, on the U.V.
spectrophotometer, with the base, t e t r a a l k y l ammonium propoxide, i n
the presence of the s a l t , sodium tetraphenylboron, due to the formation
of a white p r e c i p i t a t e .
I I I Results and Discussion :
A l l measurements were made with stoichiometric base concentration 15'
i n large excess of the substrate concentration. Data are interpreted
i n term of scheme 3.1 which takes account of the association of sodium
ions with propoxide ions and with Meisenheimer complexes.
- 67 -
P + o p r + Na
KNq,p ro"
k-P.OPr + Na
K , , x Na,ROP r
P + Na,P rO" k,
k, ip R O P r , Na
SCHEME 3.1
The value of the ion-pair association constant K^a+ p r o-> o f
40 sodium ions and propoxide ions has been determined conductometrically as 672 1 mol - 1. Previous work from t h i s laboratory has used ion concentrations rather than a c t i v i t i e s . However as indicated by Gold and
127
Toullec we can include a c t i v i t y c oefficients as described i n
chapter 1, (where R = QPr and M = Na). For propanol solvent the Debye-
Huckel parameters are: A = 3.9, B = 6.5 m o l - 1 ! nm - 1 and q (Bjerrum
distance) = 1.4 nm, and as mentioned i n chapter 1, the two unknowns
a and y were evaluated by i t e r a t i o n . For example with a stoichiometric -3 -1
base concentration of 10 mol 1 , a has the value 0.75 and y the
value 0.82.
Rate co e f f i c i e n t s were always determined under f i r s t - o r d e r
conditions with base as the excess component and equations 1.42, 1.43
and 1.44 w i l l apply.
Data fo r a-complex formation were obtained with the f i v e substrates
detailed below; and the rates of nucleophilic substitution of 1-chloro-
2,4-dinitrobenzene were also measured.
- 68 -
Measurements were made with varying concentrations of sodium propoxide i n propanol where the degree of dissociation (a) of ion
pairs w i l l decrease with increasing base concentration. The extent
of association of propoxide ions was i n some cases increased by the
addition of sodium ions i n the form of sodium tetraphenylboron. The
association of propoxide ions w i t h tetraalkylanmonium ions i s l i k e l y
to be small i n d i l u t e solution, so that the r e a c t i v i t i e s of free
propoxide ions were determined using tetramethyl-anmonium propoxide.
(a) l-Propoxy-2,4-dinitro-6-propoxy carbonylbenzene
In the presence of d i l u t e (< 0.05 mol l - 1 ) base a single colour
forming reaction i s observed giving the 1,1-complex (3.3, R = Pr,
X = 03J?r) with A 385 and 475 (Figure 3.1 and 3.2). Rates of colour & max formation, which were s u f f i c i e n t l y slow to be measured wi t h an SP500 :
spectrophotometer, and values of o p t i c a l density at the completion of
the colour forming reaction are i n table 3.1.
The data obtained i n the presence of sodium propoxide alone show
that values of K , k^ and k f increase s i g n i f i c a n t l y with increasing
base concentration. This indicates, in terms of scheme 3.1, that the value of K.. + _ _, the association constant of sodium ions w i t h Na ,P.OPr ' a-adduct, i s larger than the value of K^a+ p^-- 1° the presence of
0.01 mol l - 1 sodium tetraphenylboron, where ion-pairing w i l l be
extensive, values of equilibrium and rate c o e f f i c i e n t s are increased. Values
obtained using tetramethylammonium propoxide are much lower and represent
reaction v i a free ions. Analysis of the data using equations 1.41 -
1.44 (chapter 1) gives a value f o r p c p r _ of 10,000 1 mol - 1.
U.V/visible spectra showing the colour forming reaction are shown
in figure 3.1 (sodium propoxide) and figure 3.2 (tetramethylammonium
propoxide). A slow fading reaction i s evident ( f i g u r e 3.3) at high
- 69 -
Table 3.1
Rate and Equilibrium Data f o r 1,1-Complex Formation from 1-propoxy-
2,4-dinitro-6-propoxycarbonylbenzene (3 x 10 M) i n propan-l-ol at
10 3[NaOPr]/ [NaBPh ] / O.D. KJ 10 3k / k f/ 10 3k r/ mol mol I (475 nm) £ m o l - 1 s~* £ m o l _ 1 s _ 1 s" 1
0.32 - 0.243 1840 0.87 1.0 0.54 0.39 - 0.285 1950 1.00 1.1 0.56 0.47 - 0.316 1960 0.95 1.0 0.50 0.63 - 0.363 1950 1.38 1.2 0.62 0.93 - 0.48 2880 2.20 1.7 0.60 1.24 - 0.54 3630 3.15 2.1 0.57 1.53 - 0.56 3660 3.50 2.0 0.54 2.90 - 0.61 4200 8.30 2.6 0.63 9.40 - 0,63
29.0 - 0.65 43.0 - 0.66a
0.32 0.01 0.464 5800 1.62 3.3 0.57 0.47 0.01 0.52 5500 2.40 3.7 0.67 0.63 0.01 0.58 6300 3.06 3.9 0.62 0.94 0.01 0.626 6500 4.20 3.8 0.59 1.24 0.01 0.646 6300 5.95 4.2 0.67 1.54 0.01 0.66 6200 7.30 4.3 0.69 2.97 0.01 0.70
43 0.01 0.73a
[ l O ^ e ^ r ] / mol £ _ 1
0.56 0.139 570 0.47 0 20 0 36 0.99 0.205 560 0.61 0 22 0 39 1.99 0.298 540 0.69 0 28 0 34 3.94 0.395 550 1.20 0 21 0 38 5.93 0.438 530 1.60 0 20 0 39 10.2 0.502b 610 2.50 0 21 0 35
a. This value taken to be that f o r complete conversion to complex. b. Benesi-Hildebrand p l o t gives a value of 0.58 for complete conversion.
- 70 -
tetramethylammonium propoxide concentrations (> 0.015 M with 3 x 10 M
of the parent). This may be a t t r i b u t e d t o the formation of the phenol,
because increasing the amount of base increases the amount of water (a
source of OH- ions) i n the media, as explained by scheme 3.2.
COoPr ON t
OPr
NO CO^Pr O N V
NO CO^Pr
NO
SCHEME 3.2
(b) l-Propoxy-2,4-dinitro-6-chlorobenzene
In the presence of d i l u t e base the orange-coloured 1,1-complex
i s formed with 350, 364 (sh) and 495nm. (Figure 3.4 and 3.5).
Rate and equilibrium data were measured at 495nm and are i n table 3.2.
As the concentration of sodium propoxide i s increased there i s
only a small v a r i a t i o n i n value of rate and equilibrium constants.
In terms of scheme 3.1 t h i s indicates that the values of the association
constants of sodium ions with propoxide ions and with <f-adducts are
quite close. However, values obtained i n the presence of added sodium
ions are d i s t i n c t l y higher than those obtained with tetraalkylammonium
propoxide. The data are compatible with a value of 1100 ± 100 l m o l - 1
- 71 -
I l l u s t r a t i v e Example
Using SP500 spectrophotometer at 25°C ( f o r technique see
chapter 2), the following readings (table 3.3) were obtained at
[NaQPr] = 12.7 x 10 - 3M and [Parent] = 3.96 x 10 - 5M (see table 3.2).
P l o t t i n g Log (O.D^ - O.D .) versus time gives a value for k Q^ s =
7.5 x 10~ 3s _ 1 ( f i g u r e 3.6).
We have
kobs = k f KH + k r - 3 ' 1
and
K = k /k - 3.2 c i 1 1
To obtain K,, we p l o t ^-g versus ^ N aQp rj (Benesi-Hildebrand),
where O.D ,. i s the o p t i c a l density reading at i n f i n i t y time ( f i g u r e
3.7). From the intercept of the st r a i g h t l i n e , the o p t i c a l density for complete conversion i s 0.82.
O.D, Then, K = ^
' c °-Doo - °.D 4 9 5 [NaOPr]
K c = 280 I m o l - 1 at [NaOPr] = 12.7 x 10 _ 3M and 0-D 4 9 5 = 0.64.
Substituting t h i s value i n equation 3.2 we have 280 k r = k f
kobs = 2 8 0 kr [ N a j C P r ] + k
r > t h i s gives
-3 -1 kj, = 1.7 x 10 s and from equation 3.2,
k f = 0.46 I m o l _ 1 s _ 1 .
(c) l-Propoxy-2,4-dinitrobenzene
There i s a fast reaction producing the 1,1-complex (3.3, X = H, R = Pr) with A 495nm. A much slower reaction yields 2,4-dinitrophenol, max Because of the rather low s t a b i l i t y of the complex i t was necessary to
use f a i r l y high concentrations of the parent t o obtain measurable o p t i c a l
densities. The data i n table 3.4 show that values of Kc are independent
of the substrate concentration but increase with increasing sodium ion
concentration. This indicates that a-adduct i s more s t a b i l i s e d by
- 72 -
Table 3.2
Rate and Equilibrium Data for 1,1-Complex Formation from 1-Propoxy-
2,4-dinitro-6-chlorobenzene (4 x 10 _ 5M) in propan-l-ol at 25°.
lO^NaQPr] / [NaBPhJ/ O.D. K / 10 3k / k / 10 3k / -1 -1 -1 -T -1 -1 -1 mol I mol l (495 nm) I mol s l mol s s
1.01 - 0.191 300 1.5 0.35 1.2 2.00 - 0.305 300 2.4 0.45 1.5 3.9 - 0.464 330 3.3 0.48 1.4 6.7 - 0.56 320 5.3 . 0.54 1.7
12.7 - 0,64 280 7.5 0.46 1.7 25.3 - 0.74 370 14 0.50 1.4 64 - 0.79 -.28 - 0 . 8 l a -
1.01 0.02 0.292 460 1.9 0.60 1.3 2.00 0.02 0.426 430 3.3 0.76 1.8 3.9 0.02 0,59 450 4.3 0.70 1.6 6.7 0.02 0.66 380 7.8 0.82 2.1
25.3 0.82 — — — —
128 0.91 b
3[NMe CPr] / mol £
10
0.98 0.161 266 1 05 0 22 0.85 1.95 0.257 250 1 1 0 19 0.75 3.86 0,43 300 1 5 0 21 0.70 6.72 0.52 290 2 1 0 21 0.75 9.4 0.58 290 2 7 0 21 0.75
18.1 0.65 260 5 2 0 23 0.90 98 - 0.75 C
a. Value of 0.82 taken for complete conversion to complex. b. Value of 0.92 taken for complete conversion to complex. c. Value of 0.79 taken for complete conversion to complex (Benesi-
Hildebrand).
- 73 -
Table 3.3
Specimen data for reaction of l-propoxy-2,4-dinitro-6-chlorobenzene (4.0 x 10 - 5M) with sodium propoxide (1.27 x 10 2M) in propan-- l - o l at 25°C.
Time (sec)
°-D495 O.D - 0.D„O(. °° 495
Log (O.D, -
15 0.11 0.53 -0.275 30 0.17 0.47 -0.327 45 0.22 0.42 -0.376 60 0.27 0.37 -0.431 75 0.31 0.33 -0.381 90 0.34 0.30 -0.522
120 0.49 0.24 -0.619 150 0.46 0.18 -0.744 180 0.50 0.14 -0.853 240 0.55 0.09 -1.045 300 0.585 0.055 -1.259 360 0.61 0.030 -1.522 420 0.625 0.015 -1.823 540 0.630 0.01 -2.0
sodium ions than i s the propoxide ion. The data f i t equation 1.41
(chapter 1) with K, 5 x 1 0 - 3 I mol - 1 and I ^ a + p Qpr-, 1500 ± 200 l mol
Because of the low s t a b i l i t y of the a-adduct the rate process
involving i t s formation i s dominated by the k r term (equation 1.44 in
chapter 1). Thus measurements by stopped-flow yielded values of k
The value in the presence of sodium ions, where ion-pairing w i l l be
largely complete, i s smaller than that for reaction of free ions and
t h i s decrease largely accounts for the increase in value of in
the presence of sodium ions.
To i l l u s t r a t e how k ^ i s obtained by the stopped-flow technique,
the two s e t s of data are displayed, table 3.5 for sodium propoxide
(50 x 10 _ 3M), where the o p t i c a l density at i n f i n i t y i s 0.0223 =
log (5.1/4.845) and table 3.6 for tetramethylarnnonium propoxide
- 74 -
Table 3.4
Equilibrium and Rate Data for 1,1-conplex Formation from 1-propoxy-
2,4-dinitrobenzene in propan-l-ol at 25°.
1 0 ^ NMe4CPr] / [ Parent] / 0. D.a l O 3 ^ / /
mol £ - 1 mol 2,"1 (495 nm) I mol - 1 s - 1
2.9 0.144 0.045 5.0
5.9 0.143 0.090 4.8
9.7 0.142 0.150 5.0
19.6 0.138 0.265 4.5
19.6 0.034 0.065 4.4
27.3 0.034 0.100 4.9
50 0.012 - - 3.14
3r 10 3[NaCPr] / -1 mol l
2.64 0.144 0.065 7.8
4.76 0.140 0.120 8.2
8.7 0.142 0.24 8.9
10.2 0.05 0.11 9.8
10.2 0.14 0.29 9.1
49 0.019 0.19 9.5
50 0.012 1.27
a. Corrected for absorption by parent and base.
b. Assuming an extinction c o e f f i c i e n t of 22,000 (Ref. 99).
c. This corresponds to k .
- 75 -Table 3.5
Specimen data for reaciton of l-propoxy-2,4-dinitroben2ene with sodium propoxide measured by stopped-flow spectrophotometer at 25°.
Time (sec) V ( v o l t s ) Log ( V - V J 0.1 7.5 4.4 0.643 0.2 7.1 4.0 0.602 0.3 6.6 3.5 0.544 0.4 6.2 3.0 0.477 0.5 5.8 2.7 0.431 0.6 5.5 2.4 0.380 0.7 5.2 2.1 0.322 0.8 5.0 1.9 0.278 0.9 4.7 1.6 0.204 1.0 4.5 1.4 0.146 00 3.1 _ —
Table 3.6
Specimen data for reaction of l-propoxy-2,4-dinitrobenzene with tetramethylammonium propoxide measured by stopped-f low spectrophotomet< at 25°.
Time (ms) V ( v o l t s ) (V-V ) CO
Log ( V - V J 50 6.0 4.2 0.623
100 5.4 3.6 0.556 150 4.9 3.1 0.491 200 4.4 2.6 0.414 250 4.0 2.2 0.342 300 3.7 1.9 0.278 350 3.5 1.7 0.230 400 3.2 1.4 0.146 450 3.0 1.2 0.078 500 2.8 1.0 0.0 00 1.8 — —
[ Base] = 50 x 10 - 3M ) [Parent] = 1 x 10 _ 5M )
for both above tables.
- 76 -
(50 x 10 - 3M), where the o p t i c a l density at i n f i n i t y i s equal to 0.0096
Log (5.0/4.89). Two straight l i n e s for both s e t s of data (table 3.5
and 3.6) are shown in figure 3.8.
We can show numerically, the low contribution of k f r e l a t i v e to
From table 3.4, the average value for K £ - 0.005 I m o l - 1 ( f o r NMe^QPr),
where K = k„/k , and k. = 0.005 k , substituting t h i s value at the c f' r f r' following equation : k Q b g = k f£(Pr -] + k^ = 3.14 s ~ \ where £0Pr~] =
50 x 10 - 3M (of NMe4CSV). This gives k f = 0.0157 I m o l - 1 s - 1 ( i f k r = kobs^ ' 3 0 kf[OP r~] i s much l e s s than k^^. Similar treatment can
be car r i e d out for sodium propoxide (50 x 10 _ 3M), assuming k^ =
0.0085 k r at k Q b s =1.26 s - 1 , which gives k f = 0.0108 l m o l _ 1 s _ 1 .
(d) 1,3,5-Trin itrobenzene
In the case of the three previous substrates c-complex formation
r e s u l t s in the formation of 1,1-dipropoxy complexes, (3.3) and the data
indicate t h e i r strong interaction with sodium ions. The a-complex
formed from 1,3,5-trinitrobenzene has structure (3.1, R = Pr) in which
addition occurs at an un-substituted ring-position and the r e s u l t s
here indicate a much weaker interaction with sodium ions. Rates of
complex formation measured by stopped-flow spectrophotometry are given
in figure 3.9. We take the data obtained using tetramethyl ammonium
propoxide to represent reaction of free ions and the slope and intercept 4 -1 -1
of the l i n e a r plot y i e l d values of k (8.6 ± 0.6) x 10 l mol s and k 10 ± 1 s~^. Combination of these values gives K(= k/k_), (8.6 ±
3 -1 1.5) x 10 l mol . Measurements were also made with sodium propoxide in media containing 0.03 mol fc-1 sodium tetraphenylboron; ion association
4
w i l l be extensive here and the l i n e a r plot y i e l d s values of k f, 4 x 10
I m o l _ 1 s _ 1 and k r, 10 ± 1 s - 1 giving K c, 4 x 10 3 I mol - 1. This r e s u l t
indicates that the r e a c t i v i t y of sodium propoxide ion-pairs i s smaller
than that of free propoxide ions.
33
- 77 -
The data obtained with sodium propoxide alone i s quite s i m i l a r to that with tetraalkylaninonium-propoxide. This i s to be expected since we calculate (equations 1.39 and 1.40 in chapter 1) that in the most concentrated base solution used >80% of the sodium propoxide w i l l be dissociated. Some downward curvature of the plot at high base concentration i s expected but i s not apparent in the concentration range we have used.
These r e s u l t s are in reasonable accord with those of Gan and Norris
who, using sodium propoxiee, obtained values of 92,600 l mol~*s -^
and k r 11.9 s - 1 .
Specimen data, using the stopped-flow technique at 480 nm are
shown in tables 3.7, 3.8 and 3.9 and in figure 3.10.
In terms of equation 1.41 the decrease in value of K in the presence
of added sodium ions indicates that the value of IC T +,_ „~ - i s lower wa 'P.GPr
than that of K^ a+ Qpr~. Assuming that the sodium tetraphenylboron i s
completely dissociated and that a c t i v i t y c o e f f i c i e n t s may be calculated
using equation 1.40 we obtain a value for K^a+ p Q>r- of 250 ± 50
I mol - 1.
(e) l-Propoxy-2,4,6-trinitrobenzene
Examination by stopped-flow spectrophotometry shows the presence
of two colour forming reactions which are well-separated in time. The
^H.n.m.r spectra indicate that these give the 1,3-adduct (3.2, R = Pr,
X - N0 2) and the 1,1-adduct (3.3, X = NOg, R = Pr) and that the l a t t e r
i s the thermodynamically more stable ( f i g u r e 3.11). The r e s u l t s are
described by scheme 1.5 (page 13). Since the time-scale of the two
processes was well separated equations 3.3 and 3.4 w i l l apply where the
subscript denotes the position of addition. k f a s t = k-3 + k
3 [ P l ° " ] 3 " 3
- 78 -Table 3.7
Specimen k i n e t i c data for reaction of 1,3,5-Trinitrobenzene (10 M) -4 o
with tetramethylammonium propoxide (5.5 x 10 M) at 25 . Time (ms) v
480nm ( V 4 8 0 - V ^ ^ ( V 4 8 0 - V ^ 5 7.4 7.0 0.845
10 5.7 5.3 0.724 15 4.4 4.0 0.602 20 3.4 3.0 0.477 25 2.7 2.3 0.361 30 2.1 1.7 0.230 35 1.8 1.4 0.146 CO 0.4 — _
Table 3.8 r—
Specimen k i n e t i c data for reaction of 1,3,5-Trinitrobenzene (10~°M) -4
with sodium propoxide (5.5 x 10 M) at io n i c strength of 0.03 M (NaBPh,) and at 25°.
Time (ms) V480nm ^ 4 8 0 - ^ ^ <V480-V->
20 5.6 4.8 0.68 40 3.5 2.7 0.431 60 2.3 1.9 0.176 80 1.8 1.0 0.0 100 1.3 0.5 -0.301 120 1.1 0.3 -0.522
oo 0.8 — —
Table 3.9 _5
Specimen k i n e t i c data for reaction of 1,3,5-Trinitrobenzene (10 M) -4 o
with sodium propoxide (5.5 x 10 M) at 25 . Time (ms) V480nm ( V480- V~> ( V480
3 4.0 3.6 0.556 5 3.5 3.1 0.491 10 2.8 2.4 0.380 15 2.2 1.8 0.255 20 1.8 1.4 0.146 25 1.4 1.0 0.0 30 1.2 0.8 -0.097 35 1.0 0.6 -0.222 40 0.9 0.5 -0.301 45 0.8 0.4 -0.398 oo 0.4 —
- 79 -
kslow k - l + 1 + K^PrO"] " 3 , 4
In the presence of sodium ions, ion-pairing w i l l modify the constants to
k_ . , k „ . , k- . and k ., . . 3,ip' -3,ip' l , i p - l . i p Rate and equilibrium data are in table 3.10. The r e s u l t s obtained
with tetramethylanmoniumpropoxide w i l l represent reaction of free ions.
A l i n e a r plot according to equation 3.3 yielded value of k^, 4500
I m o l _ 1 s - 1 and k_ 3, 16 s " 1 giving K 3(= k 3 / k _ 3 ) , 280 l mol" 1. This
value i s in good agreement with that obtained independently from the
optical density measurements. The corresponding data obtained with
sodium propoxide containing added sodium tetraphenylboron gave values
of k . , 2400 l m o l ^ s - 1 , k . , 19 s " 1 and K . , 125 £ mol" 1. The o, ip —o, lp o, lp lower values of the equilibrium constant and rate of base addition
obtained in the presence of sodium ions are consistent with a rather
weak interaction of the 1,3-complex with sodium ions. This behaviour
i s i n l i n e with that of 1,3,5-trinitrobenzene where base addition a l s o
occurs at an unsubstituted ring-position.
The thermodynamic s t a b i l i t y of the 1,1-complex i s very high and -4 -1
conversion i s > 95% in solutions containing 1 x 10 mol I base.
A consequence of t h i s high value i s that in equation 3.4 the forward
rate w i l l be dominant. The value of k^, 28 I mol~ 1s~ 1 i s s i g n i f i c a n t l y
lower than that of k„ . 50 a mo, - 1s - 1 consistent with s t a b i l i s a t i o n
of the 1,1-complex (and the t r a n s i t i o n s t a t e leading to i t ) by sodium
ions.
Independent evidence for the association of the 1,1-complex with
sodium ions comes from v i s i b l e s p e c t r a l changes brought about by the
addition of sodium tetraphenylboron to solutions of the complex in
propan-l-ol (figure 3.12). The spectrum of the complex in very d i l u t e
sodium propoxide solutions shows maxima at 412 and 485 nm with a minimum
- 80 -
at 445 nm (fi g u r e 3.12). The main e f f e c t of increasing the sodium ion concentration i s to decrease the o p t i c a l density at the minimum. However, the o p t i c a l density at 412 nm i s un-affected by change in sodium ion concentration. Using the r a t i o s of O.D (412 nm)/0.D (445 nm) given in table 3.11. I t i s possible to calculate a value for the equilibrium constant for the reaction:
P r O w O P r PrOv£)Pr NO.
+ Na + K N a £ O P f
O NnJ
» Na
NO.
ION-PAIR J . P
W . C P ^ M / [ C ] K ] I f we represent the r a t i o O.D (412 nm)/0.D (445 nm) by the function
x, then
[ l . P ] / [ c ] = (x - 1.67)/(2.20 - x)
The values give K^+.p Qpv~, 1000 ± 500 I m o l - 1 (see table 3.11).
Table 3.11
Variation of sp e c t r a l shape with ion-association.
Total Free O.D (412 nm)/O.D (445 nm)
a.
b.
0 0 1.67 -4b
8.5 x 10 6.5 x 10" 4 1.83 1.15 x 1 0 " 3 b 9.0 x 10~ 4 1.89 1.4 x 1 0 " 3 b 1.1 x 10" 3 1.93 1.75 x 1 0 " 3 b 1.35 x 10~ 3 1.96 2.75 x 10 " 3 b 2.4 x 10~ 3 2.05 4.75 x 1 0 " 3 b 4.2 x 10" 3 2.20 Measured using tetramethylammonium propoxide
-4 Solutions contain 7.5 x 10 M sodium propoxide.
- 81 -
( f ) l-Chloro-2,4-Dinltrobenzene
The rate c o e f f i c i e n t s for the nucleophilic substitution reaction
y i e l d i n g l-propoxy-2,4-dinitrobenzene were measured in propan-l-ol
at 25°C. ScorranO and co-workers^ 3 5 have shown that the reaction of
potassium isopropoxide with l-halo-2,4-dinitrobenzenes in isopropanol-
benzene may occur v i a a r a d i c a l mechanism giving 2,4-dinitrophenol
(see chapter 1). The l a t t e r compound was not a major product of our
reaction and we conclude that reaction occurs by the usual S NAr mechanism'
Measurements, (table 3.12), were made using tetramethylammonium
propoxide where reaction i s l i k e l y to occur v i a free propoxide ions and
in sodium propoxide solutions containing added sodium tetraphenylboron
where the base w i l l be largely ion-paired. That the second-order rate
constant i s smaller in the l a t t e r case shows that the r e a c t i v i t y of
sodium propoxide ion-pairs i s reduced r e l a t i v e to free propoxide ions
with the implication that the intermediate complex 3.4 and the t r a n s i t i o n
state leading to i t
NO
N0 2
( 3.4)
do not associate strongly with sodium ions. This can be compared with 51
the observation that in methanol-benzene mixtures the reaction of
potassium methoxide with l-chloro-2,4-dinitrobenzene i s accelerated
by the addition of crown-ether which w i l l d i s s o c i a t e the base.
IV Ion Association
Rate and equilibrium data for reaction v i a free ions or ion-paired
species are summarised in table 3.13. The f i n a l column of t h i s table gives values
- 82 -
Table 3.12
Rate Coef f i c i e n t s for Nucleophilic substitution of l-chloro-2,4-
dinitrobenzene with propoxide in propan-l-ol at 25°.
103[NMe4QPr] / ^ o b s / W [ m e ^
mol £ - 1 s - 1 (a m o l _ 1 s _ 1 )
4.7 0.85 0.18 9.3 1.84 0.20 17.8 3.0 0.17 26.7 5.1 0.19
! [NaOPrJ / [NaBPhJ / i o 3 k a , / obs'
k o b s/[NaOPr]
mol £ - 1 mol l -1 s («, m o l - 1 s - 1 )
4.7 0.05 0.39 0.085 9.5 0.04 0.84 0.090
19 0.03 1.55 0.080 28.5 0.02 2.70 0.095
a. The reaction was followed by the increase in absorption at 300 nm due to the product l-propoxy-2,4-dinitrobenzene.
for the association constants with sodium ions of the a-complexes. I t i s
noteworthy that the 1,1-dipropoxy complexes associate much more strongly
than do the complexes where base addition occurs at an unsubstituted
ring-position. Hence we prefer a structure 3.5 for the ion-associate in
which the cation i n t e r a c t s with the oxygen atoms of the propoxy groups
and the ortho-substituents. The high value for K^a+ p Qpr- when a carbonyl
containing substituent i s present at the 6-position adds to the strength
of t h i s argument.Weak association of complexes of types 3.1 and 3.2 with
cations may involve structures analogous to (3.5) where the cation i s
near the added propoxy-group or a l t e r n a t i v e l y (3.6) where the cation i n t e r
acts with the negative charge on a nitro-group.
The e f f e c t s of ion-association on the rate c o e f f i c i e n t s for forward
and reverse reactions w i l l depend on the strength of the interaction of
Pk r-l O I • r
+" ci
O O O O Q O o o o o LO o m i-( m o co oo
m CM
+-> ci
I
a i •H i—l Q S
i
x
CO
I O
t> CO
r-l O
d o m
CO o
X X
CM*
CO CO
CO t H
CO
•s
ft O O r-l o m o 00 o
I o
T
m co o o
X CM
A
X m CM
t H t H r-l X r-l 1 X X • i o CO
CO CO r-l rH 00 m co' t>
t H CO 1 O o w r-l t H
t H CO 1 r-l r-l r-l CO X X r-l CM CM o CM X Q • • • CD m O o o •
00 tp <=^
CO m CO r-l 1 o o 1 o T - l rH
i—1 o o T - l o Q to CO X X oo m CM X CM CM CO
m A •
ft
OS w CP
ci
a
oo
+-> o
CO
r - l
^ M
X
CO
CI
K g" sr II II II II
X X X X
CO CO CO T - l CM
CO CO CO CO CO CO
- 84 -
R-OwOPr x O N NO
NO 0\. 0 ( 3.6 (3.5
sodium ions with the reactants,transition states and products. In the
case of the 1,1-dipropoxy complexes the rate c o e f f i c i e n t s for the
forward reaction are i n general increased in the presence of sodium
ions while the rate c o e f f i c i e n t s for the reverse reactions are decreased.
However for (3.3, X = CO^r, R = Pr) both forward and reverse rate
c o e f f i c i e n t s are increased by sodium ions indicating very strong
interaction of the t r a n s i t i o n s t a t e with cations. The rate c o e f f i c i e n t s
for formation of (3.1, R = Pr) and (3.2, X = N0 2 > R = Pr) are decreased
in the presence of sodium ions in agreement with t h e i r weak association
with cations.
The rate c o e f f i c i e n t for the nucleophilic substitution reaction
of l-chloro-2,4-dinitrobenzene with tetramethyl anmonium propoxide was
found to be 0.18 I mol^s-''' while the value for sodium propoxide containing
added sodium tetraphenylboron was 0.085 l m o l ^ s - 1 . That the second order
rate c o e f f i c i e n t i s smaller i n the l a t t e r case shows that the r e a c t i v i t y
of sodium propoxide ion-pairs i s reduced r e l a t i v e to free propoxide
ions with the implication that the intermediate complex does not
associate strongly with sodium ions.
V Comparison of Propoxide Adducts with those from other Alkoxides
The data obtained in very d i l u t e solutions of tetramethyl -
ammoniumpropoxide are l i k e l y to be free from the e f f e c t s of ion association.
Data are summarised in table 3.14 where they are compared with s i m i l a r
- 85 -
data for addition of other alkoxides in the corresponding alcohols. 11 32
As has been found in other systems ' the 1,1-dialkoxy complex
(3.3, X = N02, R = Pr) has considerably greater thermodynamic s t a b i l i t y
but i s formed l e s s rapidly than i t s 1,3-isomer (3.2, X = NO , R = Pr)
or the adduct (3.1, R = Pr) formed from 1,3,5-trinitrobenzene. This
enhanced s t a b i l i t y of 1,1-adducts has been attributed to release of 52
s t e r i c s t r a i n on addition at the 1-position or to the s t a b i l i s i n g 102
influence of multiple alkoxy substitution . Recent evidence from
heterocyclic systems indicates that both factors may be important.
Comparison (table 3.14 column 7) of the data for propoxide and 104
isopropoxide additions shows that as expected from solvent b a s i c i t i e s
the isopropoxide adducts have the greater thermodynamic s t a b i l i t i e s .
Addition at unsubstituted positions, where s t e r i c e f f e c t s w i l l be small,
gives values of K(PrO~)/K( isoPrO") l e s s than 0.03. Values of t h i s r a t i o
for addition at alkoxy substituted positions range from 0.063 to 0.37.
I t might be argued that since the isopropoxy group i s s t e r i c a l l y more
demanding than the propoxy group there should be greater s t e r i c r e l i e f
on addition of isopropoxide to the 1-position of l-isopropoxy-2.4-
dinitro-6-X-benzenes than on propoxide addition to the corresponding
1-propoxy compounds. However 1,1-diisopropoxy complexes containing
bulky substituents at the 2- and 6- positions w i l l themselves be subject
to unfavourable s t e r i c interactions so that the expected increase in
s t a b i l i t y i s not r e a l i s e d .
The value of the r a t i o K(PrO~)/K(EtO~) i s largely independent of
the substrate indicating that in these systems the s t e r i c requirement
of the propoxy-group i s not markedly greater than that of the ethoxy
group.
- 86 -
Table 3.14
Comparison o f Equilibrium and Rate Data f o r Alkoxide A d d i t i o n s
Structure 3.3 K/ k _ / K(Pro ) K(Pro )
Structure 3.3 £ mol - 1 I mol" 1s~ 1 s " 1 K(Eto~) K(isoPro
R
Pr
X
N0 2 >2 x 10 5 28 <1 -4 .4 x 10 5.6 0.37
Pr CO^r 560 0.21 3 .8 x 10" 4 5.3 0.25
Pr CI 280 0.21 7 .5 x 10" 4 3.3 0.063
Pr H 5 x 10~ 3 0.016 3.1
Et N0 2 3 x 10 5 17 6 x 10~ 5
E t COgEt 100 0.13 1 3 x 10~ 3
Et
Et
CI
H
53
1.5 x 10~ 3
0.14
0.01
2 6 x 10~ 3
7
isoPr 1500 0.11 7 x 10~ 5
isoPr C l 1100 0.10 1 x 10" 4
isoPr H 0.08 0.01 0.12
S t r u c t u r e 3.1
Pr 8.6 x 10 3 8 .6 x 10 4 10 4.3 <0.03
E t 2 x 10 3 4
4 x 10 20
isoPr >3 x 10 5 1 6 x 10 5 < 1
Structure 3.2
Pr N0 2 280 4. 5 x 10 3 16 4.0 <0.003
Et N0 2 70 2. 1 x 10 3 30
isoPr N0 2 >1 x 10 5 8 x 10 3 <0.1
- 87 -
I t i s of in t e r e s t that for addition at unsubstituted ring positions, where we expect s t e r i c e f f e c t s to be small, the rate constants for alkoxide addition are in the order i s o PrO~ > PrO~ > EtO~ p a r a l l e l i n g the s t a b i l i t i e s of the complexes. However, for formation of the 1,1-dialkoxy complexes the order, with respect to s i m i l a r l y activated substrates, i s PrO~ > EtQ - > iso PrO~. This inversion probably r e f l e c t s the greater s t e r i c hindrance on approach of the reagent associated
O Q 1 1 "1
with 1,1-complex formation ' .
VI Structural Study Using N.M.R. technique
%.n,m.r. spectra were measured (see chapter 2) and the s p e c t r a l
data for the parent compounds in ^Hg DMSO are in table 3.15.
The addition of 1 mol.equiv. of sodium propoxide in propan-1-
o l to solutions in DMSO of 1-propoxy-2,4-dinitro-6-X-benzenes gave
r i s e to spectra consistent with the formation of 1,1-complexes. D e t a i l s
Table 3.15 H N.m.r. parameters for parent 3 , molecules in DMSO
Ring Propyl' 3
1 Propoxy-2,4,6-trinitrobenzene 9.08 4.16(t) 1 69(st) 0.91(f)
l-Propoxy-2,4-dinitro-6- ' 8.97(d) 4.32(t) 1 74(m) 0.98(t) propoxycarbony1ben zene 8.70(d) 4.11(t) 1 74(m) 0.92(t)
1-propoxy-2,4-dinitro- 8.74(m) 4.18(f) 1 79(st) 0.98(f) 6-chlorobenzene
' 8.71(d) l-Propoxy-2,4-dinitrobenzene 8.48(d,d) 4.26(f) 1 77(st) 0.97(f)
7.57(d)
a. d = doublet, t = t r i p l e t , s t = sextet, m = multiplet b. Coupling i s observed J 6.5 Hz.
- 88 -
are i n table 3.16. The solvent composition was usually 50/50 (V/V)
although to obtain appreciable conversion of l-propoxy-2,4-dinitro-
benzene t o complex 70% DMSO was required. In the case of 1-propoxy-
2,4,6-trinitrobenzene t r a n s i t o r y bands at 6 6.23 and 8.53 ( J , 2Hz)
were observed due to the 1,3-complex (3.2, X = N0„, R = Pr).
Table 3.16
Chemical s h i f t Data f o r 1,1-adducts
Structure 3.3 Ring OCH a
X R
NO
0 0 ^
Pr
Pr 8.78(d) 8.39(d)
' 8.68(d) 7.40(d)
8.63
3.00(t) 4.10(f)
3.08(f)
Pr 3.06(f)
H Pr ' 8.67(d) 7.15(d,d) 5.0(d)
2.95(f)
a. The bands due t o other protons i n the a l k y l chain are hidden by solvent.
s U O z
13
o, CM
.CM
o CM
o to O
o 0
O A B S O R B A N C E
>>
o v o ft r H O
X P.
X
i r H vO
1 o c u
c «
• H
c Cd • H - P T ) c 1 O t o T i
i H 1 O CO >> c X 3 o p. to p o • H o u ft CD ft £ 1 • H
rH • P
<M * —
o ss dtO v< I O
• p r H o W) CD X c p. cd to • o C o — - CD
• H <D +> c EH
CD N o
o c O to CD V A
. P (Si rt
r H +* CD >> cti
i H c .O O u • H p< CO O
• H a > o r-HO
• 1
II
RE
on H I H . 1
csi rn
00 O o m CM o
2
E c
ID
> <
33NVQ^OSQV
>> , o is
X r H
o X CD p E o rH • H u - P (X t n
O 1 n
i
it
o • H r-l cc -p •p • H tic
o c • H o
r H o J - O
1 0) C\i rH 1 I EH >> c • X rt o o PL vn p, o CM o J-i u P, -p p c nJ
rH • H de
«M —N • H o X
in o i o PL
r H o - P rH O X PH 0> P E I/} •
•r-l
C • — c o o
• H 0) E - P E P cu «? U N rH O C >> V) CD
rQ rQ - P • a o
rH E E CD >> CCj
rH C U i • rO O • P • H rQ Q! cn rH •p •r-l > o s CO
• I
M l
I
oO LTl
3DNVG^0S9V
H O
>> • H X C o o < p. E o E E r4 (ti o p. i—I U 1 >> •P, 1 •+->
o CO £ E
+» •H • H P -p
-P • H 0) , C
1 •p 4 J
• H ••
« &: Q)
1 i C >> rH C X X o ON p- o o CVi u <s p. 1
rH ith
<&
C\! o s ^ i H
4^ O X
P. 10 C O
• H 4-5 P. fn O m & cvj CD
rH r Q •i~1 CO
>
o ft
CA
CD c CD N C o> r Q rH >> r! O r Q rH cd o
4^ 03
rH o I
I — :
I
p o f-l p. p
• H
0) • H
X o p o 54 P
C M • I
C M 1
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FIG. 3.6
k05 >
103%
r1.9
=21
©
\ OPr
:0.9 \ N ° 2 \
\ DATA IN TABLE 33 — \ P \ o o Q» \ s s
n-5 § \ \
\ \ \ o
\ \
TI ME (mi n.J 1 2 3 4 5 6 7 8 9 10
•oJ 1 1 • » • I
FIGUr-v 3 5
A p l o t o f Log ( O.D^ - C D ) ve r s u s t i m e f o r t h - r e a c t i o n o 1-propoxy - 2 . 4 - d i n i t r o - ^ - c h l o r o b e n z e n e w i t h sodium p r o t o x i d e Data are i n t a b l e 3.3 .
O
a. o
O
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G \ \
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\
o o . o
o o
o o 00
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FIG. 3.8 " ^ N02
n .3
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DATA IN TABLE 3.5
TIME(SEC) i 1 I I 1 L.
01 Q2 0.3 OA 05 0.6 0.7 0.8 0.9 1.0
2, NMeOPr
N02 -.6 X
N ©
,5 DATA IN TABLE 3.6
.4
3
\ 6 h2
50 100 150TIME(ms) 250 300 350 400 500 — I 1 1 1 1 I 1 I I ~>o
FIGURE 3.8
Specimen d a t a f o r r e a c t i o n o f l-t)ro'ooxy-? !,^-dinItroben7ene w i t h sodium p r o p o x i d e (above) and tetramethylammonium p r o p o x i d e ( b e l o w ) measured by stonped- f l o w s p e c t r o p h o t o m e t r y
80
70 F I G . 3-9
60 0
50
1/1 40 X3
30
20
10
1 8 0 KTlBosel / M
FIGURE 3.9
Rate c o e f f i c i e n t s f o r t h e r e a c t i o n i n pro - o a n - l - o l o f 1,315 ~ t r i n i t r o b e n z e n e with© tetramethylammonium nropoxide„ 0 sodium p r o t o x i d e and a sodium p r o t o x i d e w i t h 0.03 mol 1 sodium t e t r a -Dhenyl boron a t ?5
in E
CO
2 5 s
m CM o «- r<4 "7 _1_ UL 1— r •'
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in
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1_ 1_ —L-l LL-
°,"o cimen data measured by s t o p p e d - f l o w f o r t h e r e a c t i o n — ' t r i n i t r o b e n z e n e (10^ r") w i t h t e t r a m e t h y l a ^ m o n i u m p r o p o x i LJJX 10 M) (above) and w i t h sodium r>ro^oxide( 5.^5 X 1CT M) ,-j>!presence o f sodium t e t r a r ^ h e n y l b o r o n (0 .03M) ( m i d d l e ) and LLI sodium p r o t o x i d e alone(5.^5 X lO^V) (below) a t 25 .
2 ! o f 1,3,5-de (5.?5 a t t he wi t h
FIG. 3.11
T1
QPr
•OPr
FIGURE _3.H H.n.m.r s p e c t r a o f l ~ p r o n o x y = ? 9 a . , 5 ~ t r i n i t r o b e n ? e n " and sodium Dropoxide i n n r o n a n o l i c d i m e t h y l s u l p h o x i d e . I n i t i a l s p e c t r a a t T l .v.-hich changes t o T2 a f t e ^ ? minutes ( a t ?5) .
PQ
ABSORBANCE
•P c rH CD
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CHAPTER 4
THE REACTICNS OF THREE NITRO-ARCMATIC COMPQUNTJ6 WITH TETRAMETrlYLAMMCNIUM HYDROXIDE AND METAL BUTOXIDES
IN t-BUTANOL CONTAINING WATER
Introduction
In t h i s part, k i n e t i c and. equilibrium data are reported f o r the
reaction of three nitro-compounds with tetramethylammonium hydroxide
and potassium and sodium butoxides in t-butanol containing water. In
a l l solvent systems studied the reactive nucleophile i s thought t o be
the hydroxide ion rather than the t-butoxide ion.
The i n i t i a l reaction of 1,3,5-trinitrobenzene with alkoxide ions i s
to give the c-adducts (3.1, R = a l k y l ) while a l k y l ethers of 2,4,6-
tr i n i t r o p h e n o l generally y i e l d the 3-alkoxy adducts (4.1) which isomerize
to the thermodynamically more stable 1,1-dialkoxy adducts (4.2). The
results have shown the importance in these reactions of ion-association
with alkali-metal cations of the alkoxide ions and the negatively
charged a-adducts (the 1,1-dialkoxy complexes associate p a r t i c u l a r l y
strongly with cations).
R O . P R OR
O N NO N O O N
NO
(4 .1 ) (4 .2 )
- 90 -
There have been relatively few reports of a-complex formation 33
involving t-butoxide ions. Gan and Norris reported kinetic data for formation of an adduct from 1,3,5-trinitrobenzene and sodium t-butoxide in t-butanol. The line a r i t y of plots of k , versus base concentration
obs was taken to indicate the absence of ion-pairing effects. However a
131
more recent study from the same laboratory of the reaction of 2,4,6-trinitrotoluene-dg with sodium and potassium t-butoxides, in which a-complex formation is thought to compete with deuteron transfer, recognises the importance of ion-association.
In order to minimise the effect of ion-pairing we have used 42
tetraalkylammonium as the counter-ion, since we have shown that in dilute solutions i t associates with alkoxide ions and o-adducts much less strongly than do alkali^metal cations.
A further complication i s the possibility that i n the presence of traces of water, t-butoxide ions w i l l be converted to hydroxide ions
109
(equation 4.1). Murto has defined an equilibrium constant (equation 4.2) in terms of mole-fractions of water, Q, and alcohol Xg u Cjj for which he quotes a value of £ 5 x 10"*.
t-BuO~ + H20 t-SuCH + OH" 4.1 - LBUO I 4 2
h a~*Buce " ^
Experimental
Two methods which have been previously mentioned to dry t-butanol 144
(see chapter 2) are d i s t i l l a t i o n from potassium, by which B.ethel obtained a product containing 0.05% (w/w) of water, or refluxing with
131
molecular sieve followed by d i s t i l l a t i o n . We obtained similar results using AnalaR t-butanol treated by either of these methods. 'H.n.m.r spectra of the dried product showed a small band due to
- 91 -
residual water whose intensity indicated a water content of 0.07% (v/v). Solutions of base were obtained by diluting with t-butanol a concentrated (ca. 2M) aqueous solution of tetramethylammonium hydroxide. This necessarily increases the water content of the solvent However, in dilute base solutions the water added in this way i s small compared with the residual water in the solvent. Thus a base concentration of 2 x 10-4M w i l l increase the water content by 0.01% (v/v). Because of the high freezing point of t-butanol (25°) measurements were made at 30° ± 0.5.
A solubili t y test was carried for some mineral salts in purified t-butanol and i t was found that sodium and potassium chloride are insoluble, while sodium perchlorate has a very low sol u b i l i t y . Sodium tetraphenylboron i s soluble to some extent in this alcohol but forms a white precipitate in the presence of tetraalkylammonium bases, which makes i t d i f f i c u l t to deal with in U.V /visible studies.
PART I 4 3 : REACTIONS WITH TETRAMETHYLANM3JIUM HYDROXIDE Results and Discussion
(a) 1,3,5-Trinitrobenzene In the presence of dilute solutions of base, prepared as above
1,3,5-trinitrobenzene gives an orange species whose visible spectrum obtained by stopped-flow or conventional spectrophotometry shows maxima
4 - 1 - 1 4 -1 at 430 nm, e, 2.2 x 10 I mol cm and 500 nm, e, 1.5 x 10 I mol cm This spectrum is typical of that of 1:1 a-adducts formed by attack on TNB of oxygen bases"'""'' so that we formulate the reaction as shown in equation 4.3. With base in excess of the nitro-compound equation 1.44 w i l l hold.
TNB + OR (3.1) 4.3
k Lobs kf[0R ] + k r 1.44
- 92 -
Table 4.1
Kinetic Data for the Reaction of 1,3,5-Trinitrobenzene with Base in t-Butanol-Water at 30°.
10 4 [Base] / % Water by Volume k v, /s 1 obs' W [ B a s e ] CD (480 ran M I mol^s-"^ 0.57 0.07 135 ± 10 2.4 x 10 6 0.030 0.85 0.07 240 2.8 x 10 6 0.030 1.15 0.07 320 2.8 x 10 6 0.030 1.0 0.32 150 1.5 x 10 6 0.030 1.0 0.57 95 9.5 x 10 5 0.030 1.0 1.07 55 5.5 x 10 5 0.028 2.0 1.08 110 5.5 x 10 5 0.032 2.0 2.08 48 2.4 x 10 5 0.028 2.0 4.08 17 8.5 x 10 4 0.028 1.0 7.07 2.4 2.4 x 10 4 0.030 1.0 10.1 1.9 1.9 x 10 4 0.030
100 50 6.5 6.5 x 10 2 0.020 100 65 5.0 5.0 x 10 2 0.015 100 80 6.5 ± 1 - 0.009 200 80 8 - 0.013 400 80 10.5 - 0.017 100 90 15 ± 1 - 0.0025 200 90 13 - 0.0046 400 90 14 - 0.0095 600 90 14 _ 0.0125
a. [TNB] is 1 x 10 M throughout. b. Measured by stopped-flow spectrophotometry with 2 mm c e l l .
- 93 -
Kinetic measurements were made by stopped-flow spectroscopy in dried t-butanol and in i t s mixtures with water. Only a single colour forming reaction was observed on the stopped-flow time-scale under a l l conditions. Data are in table 4.1. In media containing 10% water or less conversion of 1,3,5-trinitrobenzene to adduct is essentially completed at equilibrium in solutions containing very low base concentrations. This indicates very high values for K, the equilibrium constant for adduct formation, so that k^OR~J >> k . Hence the values in column 4 of table 4.1 give values of k f the rate coefficient for base attack on TNB.
In media rich in water conversion to adduct is incomplete at equilibrium. I f we assume that the extinction coefficient at 480 nm is unaffected by change in solvent we may use the equilibrium optical densities to calculate values of the equilibrium constant. Values so calculated are 35 ± 10 I mol - 1 in 80% water and 10 ± 2 in 90% water. The rate measurements in 80% water yield values of k f 140 I mol'^s - 1
and k r 5 s-"^. In 90% water the rate expression (equation 1.44 in chapter 1) is dominated by the k^ term which has a value of 14 s - 1.
One interpretation of the data is that attack by the t-butoxide ion on 1,3,5-trinitrobenzene yields the adduct (3.1, R = t - Bu). The decrease in the value of k^ with increase in water in the solvent could then be attributed to a depletion in the t-butoxide concentration via the equilibrium shown in equation 4.1 and also to a solvent effect which reduces the nucleophilicity of the t-butoxide.
A second interpretation, and one which I favour, is that the reactive species is the hydroxide ion and that the decrease in i t s nucleop h i l i c i t y with increasing water content is due to a solvent effect.
109 s -4 Using a value for K a of 5 x 10 we calculate equation 4.2 that
- 94 -
even in our dried solvent the concentration of hydroxide w i l l be ca. seven times higher than that of butoxide. I t might be argued that the t-butoxide ion should have considerably higher reactivity than the hydroxide ion. However, the t-butoxide adduct of 1,3,5-trinitrobenzene would be subject to considerable steric strain which w i l l lower i t s
132 s t a b i l i t y . Thus recent crystallographic evidence indicates that even the methoxide adduct of TNB is subject to steric strain. Further the values of rate and equilibrium constants we calculate in water
133 rich media, are similar to those reported by Bernasconi and Bergstrom for reaction of TNB with hydroxide ions in 81 : 19 water/ethanol. (Their values are k f 70 I mol - 1s - 1, k r 7 s - 1, K 10 l mol - 1).
The regular increase in reactivity of the hydroxide ions as the proportion of t-butanol in the solvent is increased can be attributed to i t s progressive desolvation. This in agreement with the observation by B e t h e l 1 4 4 that the addition of small quantities of water to t-butanol containing benzyl trimethylammonium hydroxide drastically reduces the a b i l i t y of the medium to abstract a proton from the indicator 4-nitroaniline.
Further evidence that the reactive species is the hydroxide ion comes from a study of the reaction of l-chloro-2,4-dinitrobenzene with base in t-butanol-water mixtures.
(b) l-Chloro-2,4-dinitrobenzene In the presence of tetramethylammonium hydroxide in t-butanol,
l-chloro-2,4-dinitrobenzene is converted into a yellow species whose visible spectrum is identical with that of 2,4-dinitrophenol in the same medium ( A 367nm, e, 17,500 I mol - 1cm - 1, and 410 nm, e, 17,000 l mol~''"cm_1) (figure 4.1). In media containing 1% or more of water conversion is essentially quantitative. In media containing less water 2,4-dinitrophenol is the major product as judged by U.V/visible
- 95 -
spectroscopy but conversion i s not complete. Here the visible spectra show more absorption in the 300-350 nm region than does 2,4-dinitrophenol indicating the formation of another product, possibly the t-butyl ether of 2,4-dinitrophenol. The increase with time of the absorption at a l l wavelengths above 300 nm (figure 4.1) proceeds at the same rate indicating that formation of 2,4-dinitrophenol and the side-product is concurrent rather than consecutive.
There are several possible mechanisms available for the formation of 2,4-dinitrophenol. The most straight forward is the direct S AR replacement of halide by hydroxide ion. However, the formation of radical anions upon interaction of halogenonitrobenzene with alkoxides is well documented . That these radicals may contribute to the overall
135 substitution process has been shown by Scorrano and co-workers in the
138 reactions of 4-chloronitrobenzene with alkoxides . Characteristic
135 138 features of reactions involving radicals ' are a less than f i r s t order dependence on base concentration and a susceptibility to the presence of oxygen. The data in table 4.2 show neither of these characteristics. Thus the results in rows 13 to 15 indicate a s t r i c t l y f i r s t order dependence on base concentration while those in rows 9 to 11 indicate that the presence or absence of oxygen has l i t t l e effect on reaction rate. While we cannot rule out the possibility that a small amount of reaction proceeds by radical intermediates, particularly in those media containing the least water, the data are in accord with the formation of 2,4-dinitrophenol by direct attack of hydroxide ions on l-chloro-2,4-dinitrobenzene. The decrease in reaction rate with increasing proportion of water in the solvent is shown in figure 4.2. The variation is similar to that of the TNB-hydroxide reaction, indicating that i t is very l i k e l y that the same nucleophile, OH~, is the reactive species in each case.
- 96 -
Table 4.2
Kinetic Data for Reaction of l-Chloro-2,4-dinitrobenzene with Base in t^utanol-Water at 30°.
10 3 [Base] / % Water by Volume 10 3 k Q b s/ k Q b s/[Base] OD (410 nm) M s"1 l mol "''s ^ 0.2 0.08 2.2 11 0.45 0,4 0.09 4.0 10 0.32 0.6 0.10 4.3 7 0.40 1.0 0,12 7.4 7 0.42 2.0 0.16 12.3 6 0.44 1.0 0.35 2.2 2.2 0.52 1.0 0.59 1.5 1.5 0.60 1.0 1.06 0.84 0.84 0.62
1.0 2.06 0.40 0.40 0.64 0.43b 2.10 0.18 0.42 0.63 0.43° 2.10 0.15 0.35 0.63 1.0 3.95 0.14 0.14 0.60 10 5.6 0.83 0.083 0.05 7.7 5.5 0.59 0.078 0.63
5.1 5.3 0.41 0.080 0.64 57 13 0.54 0.01 0.67 54 18 0.35 0.007 0.67 51 23 0.19 0.004 0.67 45 32 0.09 0.002 0.67
a. l-chloro-2,4-dinitrobenzene is 4 x 10~ M. b. Solutions flushed with nitrogen. c. Solutions flushed with oxygen.
- 97 -
(c) l-Chloro-2,4,6-trinitrobenzene The reaction of pic r y l chloride with dilute solutions of tetra-
nethylamfionium hydroxide in t-butanol proceeds in two stages. There is a rapid reaction giving an orange species whose visible spectrum, with maxima at 425 and 480 nm (figure 4.3), is typical of a o-adduct. This is followed by a slower reaction giving a yellow species whose visible spectrum, A 365 nm, is identical with that of pi c r i c acid
max in the same medium. Specimen data for the calculation of the rate coefficient of the slow process by Guggenheim's method is in table 4.4.
We interpret the data according to reactions shown in the scheme 4.1. The i n i t i a l l y formed adduct (4.3) might result from attach of either t-butoxide or hydroxide ions. The data relating to this reaction, table 4.3 are in accord with attack by hydroxide. Thus the decrease in the value of k^ (= kQ^s/{Base^) with increasing water in the solvent parallels the decrease in rate coefficients for hydroxide attack on 1,3,5-trinitrobenzene and l-chloro-2,4-dinitrobenzene.In media
CI
O 2
NO O N H H OH CL 0 NO (43) + HO
4 NO OH NO + CI
Scheme 4.1 NO 2
- 98 -
containing 5% or 10% water only par t i a l conversion to a-adduct is -4
achieved with 1 x 10 M base. The optical densities at completion of this reaction, but before appreciable conversion to picric acid has occurred, allow the calculation of values of K . These values together with the values of give values in 5% water of kg 1.2 x 10 4 I mol - 1s - 1
k_30.6 s - 1 and in 10% water of ^ 2.2 x 10 3 l mol - 1s - 1 and k _ 3 l . l s - 1. Comparison of tables 4.1 and 4.3shows that at a given solvent
composition values of rate constants and equilibrium constants for hydroxide attack at the 3-position of p i c r y l chloride are lower than those for attack at un-substituted position of 1,3,5-trinitrobenzene. A similar reactivity order has been found previously in studies of 157 158 methoxide or ethoxide attack on these substrates. The lower reactivity of pi c r y l chloride may be due to steric interference between the chlorine atom and the nitro-groups which disrupts the planarity of the molecule and reduces the electron withdrawing a b i l i t y of the n i t r o -groups.
159 In previous work i t has been shown that in water containing
sodium hydroxide the hydroxy-group in adducts such as (4.3) w i l l ionise to give a dianionic species. However, l i t t l e ionisation occurs in solutions containing < 10 M base. At the very low base concentrations used in the present work we would not expect appreciable ionisation of (4.3) to occur.
With time pi c r y l chloride is converted to pic r i c acid. In a l l media examined converison is > 80%. We have no evidence that reaction occurs other than by direct displacement of chlorine by hydroxide ion. Thus visible spectra show an isobestic point at 400 nm indicating the absence of any reaction intermediate such as the t-butyl ether of pi c r i c acid. The kinetic expression corresponding to the reaction sequence shown in the scheme is given in equation 4.5. At the base
- 99 -
Table 4.3
Kinetic and Equilibrium Data for the Rapid Reaction of Picryl Chloride (10 M) with Base in t-H3utanol-Water
at 30°.
1 [Base]/ % Water by kobs/ wl 'Base] OD (480 nm)a K3b/
M volume s- 1 X, mol" V 1 l mol - 1
0.5 0.07 60±10 1.2 x 10 6 0.030 — 1.0 0.07 130 1.3 x 10 6 0.030 -1.5 0.07 250 1.7 x 10 6 0.030 -1.1 0.30 50 4.5 x 10 5 0.030 -1.0 0.6 24 2.4 x 10 5 0.030 -1.0 1.1 14 1.4 x 10 5 0.028 -1.0 5.0 1.8 - 0.020 2 x 10 4
1.0 10.0 1.3 0.006 2 x 10 3
a. At the completion of the rapid reaction. b. Defined as OD (480)/(0.030-OD (480)) [Base].
- 100 -
Table 4.4 Specimen Data for Slow Process at 470 nm (from figure 4.3),
Where Guggenheim's Method is Applied. t(s) O.DA(t) O.D,(t + T) O.DA(t) - I/>g[0.DA(t O.DA(t)
O.D|t+T) O.DA(t+T)}
0 0.737 0.298 0.439 -0.357 110 0.670 0.281 0.389 -0.410 220 0.623 0.269 0.354 -0.451 330 0.575 0.253 0.322 -0.492 440 0.529 0.243 0.386 -0.543 550 0.482 0.233 0.249 -0.604 660 0.446 0.224 0.222 -0.653 770 0.310 0.210 0.200 -0.699 880 0.382 0.198 0.184 -0.735 990 0.358 0.195 0.163 -0.788 1100 0.330 0.190 0.140 -0.853
A = 470 nm , T = 1320 sec.
concentrations used to measure the slow reaction Kg[GH~]> 1, so that equation 4.5 reduces to 4.6
kobs = ^ [ r a - l / d + K 3 [ 0 T ] ) 4.5 kobs = V K3 4- 6
Measurements obtained at 480 nm are in table 4.5. They show that, as required by equation 4.6, values of k Q b e are independent of base concentration in media containing > 2% water. In media containing less water there appears to be a component of the rate which increases with base concentration. Thus the f i r s t three results in table 4.5, referring to solutions where the water content changes l i t t l e , show a marked dependence on base concentration. I t is possible that in these solutions where the hydroxide ions w i l l be least solvated and thus most reactive, attack of hydroxide occurs on the a-adduct (4.3) to give nucleophilic substitution via the di-adduct (4.4). Such an adduct would be unstable with respect to loss of chloride ion and would not be an observable
- 101 -
intermediate. That such a pathway exists in water containing high 159
concentrations of sodium hydroxide has been shown previously
CL ,OH NO, O N O N NO
H OH
N0 2 N02
(4.4) (4.5)
I t is worth noting that our kinetic data allow us to discount the possibility that the a-adduct we have observed is (4.5) rather than (4.3). The argument is as follows. I f we were to assume that the observed adduct is (4.5) then the rate constants in table 4.5 would refer to loss of chloride ion from this adduct and would give a value in 5% water
-2 -1 of 1 x 10 s . An example is shown in figure 4.3 and table 4.4 demonstrating the use of Guggenheim's method. However the measurements of the more rapid reaction give a value in the same solvent system for expulsion of hydroxide ion of 0.6 s -*. Since chloride is known to be a considerably better leaving group than hydroxide this hypothesis i s untenable.
From the known values of k ^ and we calculate, using equation 4.6, a value for kg of 200 £ mol^s - 1 in a medium containing 5% water. Since base addition w i l l be the rate-limiting step in the substitution reaction, this value refers to the rate of hydroxide attack at the 1-position of picryl chloride. The corresponding value for hydroxide
4 -1 -1 attack at the 3-position is 1.2 x 10 £ mol s in the same medium. That attack at the unsubstituted position is faster than at the chloro-
159 substituted position is in agreement with results obtained in water
V 1981 HBRAfW
- 102 -
The results, table 4.5, indicate that the rate of conversion of p i c r y l chloride to p i c r i c acid increases with water content of the solvent. This in marked contrast with the large decrease in rate of
Table 4.5 Rate Data for the 'Slow' Reaction of Picryl Chloride (4 x 10_5M) with Base in t-Butanol-Water at 30°.
4 [Base] / Volume % Water 10 4 k ( M s~
2.0 0.08 3.6 ± ( 4.0 0.09 5.2 8.4 0.11 10 30 0.22 30 50 0.32 23
4.8 1.1 33 25 1.2 42
4.8 2.1 44 25 2.2 62
4.8 3.1 67 25 3.2 84
4.8 4.1 89 25 4.2 97 5 5.0 108
10 5.0 105 20 5.0 96 50 5.0 87
100 5.0 200 10 10.0 210 20 10.0 200 50 10.0 180
100 10.0
•1 0.3
~~———— _ •" conversion of l-chloro-2,4-dinitrobenzene to 2,4-dinitrophenol with increasing water. The difference in behaviour is understandable when i t is remembered that the equation relevant to p i c r y l chloride is equation 4.6. As outlined below i t is expected that the values of both k„ and IC, w i l l decrease with increasing proportion of water in the
- 103 -
solvent. However, i f the decrease in Kg is larger than the decrease in kg then the value of w i l l increase. The change in value of Kg
with solvent composition w i l l depend on the change in energy of the adduct (4.3) relative to the reactants. A major factor contributing to the expected decrease in value i s l i k e l y to be the better solvation and corresponding lowering in energy of the hydroxide ion as the proportion of water is increased. Similarly the value of kg w i l l be expected to decrease as the water concentration i s increased. However here the relevant energy change is between the transition state for formation of (4.5) and the reactants. Since in the transition state desolvation of the hydroxide ion w i l l be incomplete the smaller decrease in value of kg can be understood.
PART I I : REACTIONS WITH METAL BUTOXIDES Results and Discussion
a) 1,3,5-Trinitrobenzene The visible spectra for 1,3,5-trinitrobenzene with sodium or
potassium t-butoxides are similar to that obtained with tetraalkyl t -butoxide (part I ) . A spectrum obtained by stopped-flow i s shown in figure 4.4 and table 4.6 and i s typical of 1:1 a-adducts (equation 4.3 and 1.44).
Kinetic measurements were made by stopped-flow spectrophotometry in dried t -butanol and in i t s mixtures with water. Only a single colour forming reaction was observed on the stopped-flow time scale under a l l conditions. Data are in table 4.7 for sodium t-butoxide and in table 4.8 for reaction with potassium t-butoxide. Conversion of 1,3,5-trinitrobenzene to adduct is essentially complete at equilibrium in solutions containing 10% water or less at the base concentrations used. According to this we expect high values for K (the equilibrium constant for adduct formation) so that k f [OR-] >> k . Hence column 5
- 104 -
of table 4.7 and column 4 of table 4.8 give values of k f (the rate coefficient for base attack on TNB which is described in equation 1.44). The value of k^ for reaction with sodium alkoxide in the "anhydrous
4 -1-1 solvent" is 4 x 10 l mol s which is close to the value obtained by
33 Gan and Norris (38,000 ± 2,000). The value is affected very l i t t l e by the presence of sodium ions i n the form of NaBPh so that i t can be concluded that reaction occurs via Na+OR~ ion pairs. The value with
4 -1 -1 the potassium base 3.7 x 10 l mol s is similar. Both these values are very much smaller than the value for reaction with tetraalkylammonium base (3 x 10 I mol~ s~ ) which w i l l be largely dissociated. These results do not of themselves indicate whether the reaction being studied involves t-butoxide attack or hydroxide attack. However the fact that the addition of water to the medium does not give rise to a second rate process might be taken as evidence that reaction involves Na+QH~ and K+QH~ ion pairs rather than the t-butoxide species.
The observed rate coefficients decrease much less rapidly on addition of water than do those obtained with tetraalkylammonium hydroxide. This may be attributed to the counterbalancing of two factors, ( i ) an increase in the extent of dissociation of ion pairs with increasing water content, ( i i ) a decrease in reactivity of free ions with increasing water content due to better solvation. In media containing 10% or more of water the rate coefficient i s v i r t u a l l y independent of the cation.
H.n.m.r spectra were taken of TNB (0.2 M) and potassium t-butoxide (0.2 M) in a 50/50 (V/V) mixture of Anala R t-butanol/DMSO-dg. Bands were observed at 6 8.43, 6.30 and 6.40, due to 1:1 adducts (the intensity ratio of the 6.30 and 6.40 bands being 2:1). I t seems possible that in this medium both QH~ and GBu~ addition is occurring and gives rise to
- 105 -
the bands at 6.30 and 6.40. In media containing 1.5% and 5% added water bands were only observed due to the hydroxy adduct at 68.43 and 6.30. The observation of a band due to a butoxy adduct may result from the relatively high concentration of TNB and base used so that no free water remains in solution,
fcj) l-€hloro-2,4 Dinitrobenzene
In the presence of potassium t-butoxide in t-butanol the visible spectra, figure 4.5, indicate the formation of 2,4-dinitrophenol. I t i s of interest that the visible spectrum of 2,4-dinitrophenol shows a distinct difference in the presence of tetraalkylarmionium alkoxide and sodium/potassium butoxide. This difference can be attributed to the different extent of ion-pairing of the 2,4-dinitrophenoxide ion with +NR^ and Na. The spectra i n figure 4.6(a) show the gradual change in spectrum as sodium ions, i n the form of NaCiO^, are added to a solution of 2,4-dinitrophenol and tetraethylanmonium hydroxide i n t-butanol.
Similarly the visible spectra of the picrate ion (figure 4.6(b)) are affected by ion association.
In media containing 1% or more of water conversion of 1-chloro-2,4-dinitrobenzene to 2,4-dinitrophenol I s v i r t u a l l y complete as judged by i n f i n i t y O.D values.
In "anhydrous" t-butanol there i s evidence for the formation of another product with absorption in the region 300 - 350 nm (figure 4.5) which may be the t-butyl ether. This side product i s formed concurrently with the 2,4-dinitrophenol.
Again we attribute reaction to give 2,4-dinitrophenol to the direct attach of hydroxide, or potassium hydroxide ion pairs, on the substrate. The rate coefficients in the "anhydrous solvent" are more than an order of magnitude lower than those obtained with the dissociated tetra-alkylanmonium hydroxide. In a given solvent ( i . e . containing a fixed proportion of water) the value of the second order rate coefficient
- 106 -
Table 4.6
Specimen Data Obtained by Stopped-flow Spectrophotometer,
for the I n i t i a l Spectrum, for KCBu (10-3M) with TNB (10 - 5M)
Dried t-Butanol at 30°C (see figure 4.4).
X(nm) V^vo l t ) o V b(volt) O.D
520 5.0 4.725 0.0245
510 5.0 4.695 0.0273
500 5.0 4.700 0.0268
490 5.0 4.702 0.0266
480 5.0 4.725 0.0245
470 5.0 4.715 0.0255
460 5.0 4.705 0.0264
450 5.0 4.640 0.0324
440 5.0 4.610 0.0352
430 5.0 4.560 0.040
420 4.8 4.420 0.0358
410 4.0 3.760 0.0268
400 3.0 2.890 0.0162
390 2.1 2.050 0.0104
380 1.4 1.379 0.0065
a. corresponds to incident light intensity.
b. corresponds to intensity after passage through the
sample.
0.0= L001VJ V]
- 107 -
Table 4 .7 Kinetic Data for
the reaction of 1,3,5-Trinitrobenzene (10~ hn) with Sodium
Butoxide in t-Butanol-Water at 30°C.
04[Base] a [ NaBPhJ % Water 4 kobs/| BaseJ °-D480 /M /M by volume s" 1 I mol - 1 a" 1
5.0 0 0.57 22 ±2 4.4 0.028
6.0 0.003 0.67 25 ±3 4.2 0.024
3.0 0.003 0.37 8.5±0.3 3.0 0.023
9.0 0.003 0.97 28 ±3 3.1 0.0255
3.0 0 0.37 10 ±1 3.3 0.0268
2.9 0 1.615 9 ±1 3.1 0.0259
6.0 0 1.665 20 ±1 3.3 0.0282
13 0 1.37 39 ±1 3.0 0.0277
34[Base] b
/M
2.36 0 0.07 10 ±1 4.0 0.0193
4.70 0 0.07 22 ±1 4.7 0.0203
7.1 0 0.07 26.810.5 4.0 0.0251
10 0 0.07 32 ±2 3.2 0.0255
15 0 0.07 56 ±2 4 0.0273
19.9 0 0.07 72 ±1 4 0.0279
25.0 0 0.07 103 ±1 4 0.0289
a. Base was prepared by diluting aqueous sodium hydroxide with t-butanol.
b. Base was prepared by dissolving sodium metal in t-butanol. c. Measured by stopped-flow spectrophotometry with 2nm c e l l .
- 108 -
Table 4.8
Rate Data for 1,3,5-Trinitrobenzene (10 jvj )with Potassium
t-Butoxide in t-Butano1-Water at 30°C.
10 4[Base] a % Water by k j j ^ 10~ 4k Q b s/[Base] -1 ,-1 -1 °'D450 /M volume s l mol s
19 1.07 65±5 3.4 0.0353
19 2.0 63 3.3 0.0346
19 5.07 41 2.2 0.0348 ( t ^ l 8 s )
19 10 16±0.5 0.8 0.0338
19 20 7 0.4 0.0276
9.5 0.07 32±2 3.4 0.0361
20 0.07 79±1 3.9 0.0356
24.7 0.07 85 3.4 0.0477 ( t ^ 9 s )
30.4 0.07 115±10 3.8 0.0444
a. Base was prepared by dissolving potassium metal in dried t-butanol.
b. In some cases a very much slower reaction was observed, tXi noted.
- 109 -
decreases with increasing base concentration. This can be a t t r i b u t e d to an increase in the f r a c t i o n of base which i s ion-paired as the base concentration increases.
As the f r a c t i o n of water i n the solvent increases, the second
order rate c o e f f i c i e n t decreases, but much less rapidly than with +NR4CH~.
Two factors are involved ( i ) better dissociation of the K+0H~ ion
pairs with increasing water content and ( i i ) reduction i n r e a c t i v i t i e s
of hydroxide ions through better solvation.
An example, table 4.11 and figure 4.8, i l l u s t r a t i n g the l i n e a r i t y
of one of the rates on table 4.9,(row 7) i s included,
c ) l-Chloro-2,4,6-Trinitrobenzene
The reaction of p i c r y l chloride with potassium t-butoxide or sodium
t-butoxide i n t-butanol proceeds i n two stages. There i s a rapid reaction
giving an orange species ( t y p i c a l of a a-adduct) at 420 and 480 nm,
figure 4.7. This i s followed by a slower reaction, giving yellow
species, whose spectrum i s i d e n t i c a l with that of p i c r i c acid.
However A s h i f t s from 350 nm to 400 nm as the concentration max -4
of potassium t-butoxide i s increased from 3 x 10 M to 0.05M, corresponding
to ion-association of the pic r a t e ion with potassium ions.
Scheme 4.1 w i l l apply to t h i s reaction, where the rapid process
gives adduct 4.3 . The t h i r d column i n table 4.12 i s equal to k^,
scheme 4.1, and decreases with increasing water content in the solvent.
This behaviour p a r a l l e l s that of 1,3,5-trinitrobenzene and 1-chloro-
2,4-dinitrobenzene.
Comparison of tables4.8 and 4.12shows that at a given solvent
composition ( f o r potassium t-butoxide), values of rate constants and
equilibrium constants for hydroxide attack at the 3-position
of p i c r y l chloride are lower than those for attack at
- 110 -
Table 4.9
Kinetic Data f o r Reaction of l-Chloro-2,4-Dinitrobenzene _5
(4 x 10 M) with Potassium t-Butoxide at 410 nm in t-Butanol-
Water at 30°C. 10 3 [KCBu] ^ o b s % Water by w [ B
/M ( s 1 ) volume £ mol" 1
7 .98' .32 .07 .32
1.98 .56 .07 .283
5.12 1.05 .07 .205
10.0 1.77 .07 .177
19.5 2.52 .07 .13
39.0 4.98 .07 .105
58.5 5.09 .07 .087
78.0 6.9 .07 .088
2.45 .14 2.5 .06
4.9 .082 5.0 .017
7.3 .075 7.4 .010
9.8 .075 10.0 .0077
12.25 .11 12.4 9
.008 9.8 .46 2.0 .047
19.3 1.32 1.0 .068
- I l l -
Table 4.10
Kinetic Data f o r l-Chloro-2,4-Dinitrobenzene (g x 10~°M) with Postassium t-Butoxide i n t-Butanol-Water at 30 C.
3 [Base] a
/M % Water by volume
1 0 \ b s (s X )
°-D400 I mol s
1.98 2 0.073 0.525 .0368
1.98 4 0.056 0.520 .0283
1.98 6 0.033 0.515 .017 1.98 8 0.035 0.515 .0176 1.98 10 0.027 0.525 .0136 3.96 10 0.044 0.520 . O i l 1
5.94 10 0.052 0.520 .0087
7.92 10 0.063 0.525 9 .007
9.90 10 0.0625 0.530 .0063
a. Base was made by dissolving aqueous potassium hydroxide i n p u r i f i e d t-butanol.
b. Optical densities at completion.
Table 4.11
S)ecimen Data f o r Reaction of l-Chloro-2,4-Dinitrobenzene <4 x 10 - 5M) wit h Potassium t-Butoxide (58.5 x 10 - 3M) at 410 nm i n t^utanol-Water at 30°C (table 4.9 row 7 and figu r e 4.8).
Time(s) °-D410 O.D -O.D.1N 00 410
I/*CO.D B-O.D 4 1 0)
30 0.270 0.280 -0.553
60 0.312 0.238 -0.623
120 0.380 0.170 -0.769
180 0.425 0.125 -0.903
240 0.456 0.094 -1.027
300 0.478 0.072 -1.143 CO 0.55 -
- 1 1 2 -
Ta b l e 4.12
Kinetic Data f o r the Reaction of P i c r y l Chloride (10~°M)
with Potassium t-Butoxide i n t-Butanol-Water at 30°C.
IO3[KOBU]
/M
k w,(s 1 ) obsv ' ( f a s t process) I m o l - 1 s - 1
°-D480 3^ -1 10 k . (s x ) obsv '
(slow process)
a K 3
£ m o l - 1
% Watei by-
volume 1.0 11.6 -j- 0.3 11600 .024 6 4.6 - .07
2.0 27 + 1 13500 .025 6 6.04 - .07
3.0 38 ± 3 13700 .022 3 - - .07
4.0 62 ± 2 15500 .021 8 - - .07
5.0 83 ± 3 16600 .022 - - .07
2.0 22 ± 2 11000 .021 4 24.4 - 1.07
2.0 17 ± 6 8800 - 58.8 - 2.07
2.0 9.5 ± 0.3 4750 .021 48.4 - 5
2.0 5.2 ± 0.2 2600 .018 26.0 1800 10
2.0 3.3 ± 0.3 1650 ,010 23.7 360 20
a. Defined as 0.D(480)/(0.023-0.D(480))[Base]
- 113 -
Table 4.13
Rate Data for the Slow Colour Fading Process at 480 nm of P i c r y l Chloride with Potassium t-Butoxide i n t-Butanol-Water at 30°C.
103[KCBu]/M
0.997
2.02
4.04
6.06
10.10
1.98
4.06
2.02
3.94
10. 1
2.02
4.04
10.10
5.18
5.13
5.08
5.18
5.18
1.9
1.9
1.9
1.9
1 0 3 k o b s s" 1
5.10
4.76
4.11
4.08
4.27
26.
49.
20.
32
37
25.
28.
27.
4.76
107.4
86.5
33.7
30.8
5.76
42.3
28.3
25.9
% Water by
volume
0.07
0.07
0.07
0.07
0.07
2.0
2.0
5.0
5.0
5.0
10.0
10.0
10.0
0 .07
1.0
2.0
5.0
10.0
0 .07
1.0
2.0
10.0
^ P i c r y l ChlorideJ
/M
in i o x CO
I o X
CO
- 114 -the unsubstituted position of 1,3,5-trinitrobenzene. This low r e a c t i v i t y p i c r y l chloride i s due t o s t e r i c interference (part I , between the chlorin atom and the n i t r o groups. The same argument favouring the formation of (4.3) rather than (4.5) can be applied here as in part. 1.
As predicted from equation 4.6 rate c o e f f i c i e n t s of the slow process
are largely independent of base concentration at a given solvent com
position. They go through a maximum value as the water concentration i s
increased. This must resul t from a combination of factors, including
ion-pairing and solvation, a f f e c t i n g the r e l a t i v e r e a c t i v i t i e s of the
hydroxide ion for a-adduct formation and nucleophilic s u b s t i t u t i o n .
Conclusion
With metal butoxides another factor i s introduced here, beside the
eff e c t of water. This i s ion-association. In these media the reactive
species are s t i l l hydroxide ions, but metal ions associate with hydroxide
ions lowering t h e i r r e a c t i v i t i e s ( t a b l e 4.14).
Table 4.14
Comparison of Reactivities of Free ions or Ion-Pairs
Substrate Base kf/& m o l - 1 s - 1
TNB
l-Chloro-2,4-Dinitrobenzene
P i c r y l Chloride
NMe,OBu „ , N 6 4 ^ 3 x 10
( NaCBu or . 4 (KCBu - 4 x 10 NMe^CBu % 10
KCBu ^ 0.2
NMe40Bu ^ 1.3 x 10 6
KCBu ^ 1.3 x 10 4
* In t-butanol containing 0.07% water by volume at 30°C,
GO
r-l o c CO
j i 1 I 4-> >-•:
a1
• r-t •—• <M
• H
a: p t\ C c <U • r-! rO O 5-,
1 rH r • r-i X Ty 1 X)
- V e a • r C\. v - <D 1 CO E o J... •H o r~ O tu: x: c o • H i >> r-1
E O • H o
c C cv o E E O cd -H <r rH • H D >> to .C -H> CD <D rH E t rQ cd •r-i J-i w •p 1 • l - J a-
> -p
CV I—I tx
OD m -4* m rss
FIG. 4.2
5
CD r H i
A ©
2
0 0 0 0 3 0 L 0 % Water (by vol
FIGURE _.4-2_ V a r i a t i o n w i t h s o l v e n t c o m p o s i t i o n o f t h e r a t e c o e f f i c i e n t s f o r b-se a t t a c k on A,1„3,5-trinitrobenzene and B , 1 - c h l o r o - ? , d i n i t r o b e n z e n e For t he l a t t e r compound t h e s c a l e i s 6+ Log (k v / Bas« ) .
f w0tD-%0)D01
3
°9
I c: E-
E r-ni
0) -p
C
•3-
CD »H u o
-p a;
o
a P ,P I
P
T3 •rH
<H '£ P.
C5 -P O I
C o
p> o
<
rf-
P>
>> X ct a • H o •• p P CO
CO o CM •H O de
CD CO
Ki • H E CO Ki • H • H -P O -P O P CD CD .C E P. .o P> • H CO
E *t-' P
0) -P c CO
& c tu) C O C • H
CO E cc a; • H E ,c a" o a
- t «* T 3DNV9aOS9V
0^ I <> 5 1
W 1
& ' M '
o o 3 S 5
y3I3W0ai3dS M0ld-Q3dd0lS Q3NIV180 S3LUSN3Q IVDIIdO
t 1 o
3
a t
OM t
\ Ci t n
rH \ _IIM«HIIH nil CO ^
r-H
\ CD f CO CO
O 0)
CP
-p r V \ u -P o
-P r-1
a> o
> -p a
ID • 0 J '
8 o
r - i f t . >
ABSORBANCE 4 8
GO CSS
FIG. 4.6(a)
NO I 1 2
, N&OB& 4 tai
FIG. 4.6(b) 08
NEtOBu
350
FIGURE 4.6 WAVELENGTHS)
-5 U.V s n e c t r a f o r parent ( 4 X 10 M) and te+raethylammonium -hydroxide (1 X 10 3 M) i n p u r i f i e d t-butanol at 30°, at v a r i e d
-A — 4 _ -3 s a l t c o n c e n t r a t i o n s : ! , 1 X10 M , I I , 5 X 10 M , I I I , 1 X 10 M IV,3.5 * 1 0 3 M. (( s a l t used i s NaClO^ V
3
CNJ 0 1
o
r —
B-—
1 tS
r r;'
o
c
E--
o C
-p rc' 4
o ,e i — 1 a: o P C C'J x cc -p r- 1
< Ctf —* •r-: 1 -P •P j
73 j • H X? • r -i <U (5 o • H 0) rH ti-.' r C s: •H -P o to rH P- • H >5
c O • H P <->*
o n 1 c >
~t~ o CD O P >
CO rH - - u: Qj
r . j • H
X5 a-•l~"t <M M •H E • H
O •p -P
> X) •P> • 1 • r—
P5 -P *•
O-a
:=>
H
r->
c r
O r-H V > — m
C Xs
b C G
c
e-4 r CQ
8 -P UJ H OQ
O 4 0 0 em 8 to
8 H
ft O -p
C D CM <N1 0) (1)
CO
c 8 ILL. bf Pi
1/7 O 21 «g CU C3-
<v s o .0
8. co
m © v 9 p-» CO GN O i—' o Mn>.
0J -A I JM.M
I r a J—
ABSORB AN CE
- 115 -
CHAPTER 5
CATICN-COMPLEXING OF a-ADDUCTS IN CONCENTRATED METAL METHQXIDE SOLUTIONS
Introduction
There i s much evidence that 1,1-dialkoxy adducts such as (1.22,R=R=Alkyl)
associate strongly with a l k a l i metal cations i n alcohols. In chapter
3 i t was shown that 1,1-dipropoxy complexes undergo such association, 42 126
and there i s a considerable amount of evidence i n the l i t e r a t u r e . ' '
MeO./OMe E t Q QEt O C<
( 5 . 0 ) (5.1)
129 136 ' I t has been shown that adducts carrying a methoxycarbonyl sub-
s t i t u e n t at the 6-position (1.22, X = COgMe) associate p a r t i c u l a r l y
strongly. One point i n the present study was t o examine the association
with cations of the methoxy-adduct (5.0 ) of 2-metboxy-3,5-dinitrobenzoic
acid. In basic media the acidic function w i l l be ionised so that the
adduct w i l l carry two negative charges. There i s the p o s s i b i l i t y that t h i s
w i l l give r i s e t o a very large e f f e c t involving strong cation complexing.
A further point which i t was wished to explore was the association of 127
1:2 and 1:3 methoxy adducts w i t h cations. Gold and Toullec have
shown that the 1:2 ethoxy adduct (5.1) of 2,4-dinitrophenetole forms at
a much lower concentration of sodium ethoxide than of potassium
ethoxide and have a t t r i b u t e d t h i s t o a sp e c i f i c assocation of the 1:2 adduct with sodium ions. In the present work the formation of 1:2 and/or 1: 3 adducts.
- 116 -
from 2,4,6-trinitroanisole, N,N-dimethyl picramide, N-methvlpieramide, picramide and l - ( 2"-hydroxy ethoxy) 2,4,6-trinitrobenzene have been examined. Experimental
Concentrated solutions of base were found to absorb i n the u l t r a
v i o l e t region. A l l measurements of o p t i c a l densities were corrected
f o r absorption by the base. In some cases, notably with N,N-dimethyl-
picramide and N-methylpicramide, decomposition of the substrate
slowly occurred so that o p t i c a l densities shown i n the tables were
those extrapolated back t o time of mixing.
Attempts were made to examine the interaction of the adduct (5.0 )
with s i l v e r ions. However s i l v e r s a l t s such as s i l v e r n i t r a t e have very
low s o l u b i l i t i e s i n methanol, and i n the presence of methoxide ions
gave a brown pr e c i p i t a t e . These factors made i t d i f f i c u l t t o pursue
t h i s l i n e of investigation.
A l l measurenents were made in A.R methanol at 25°C. As a ru l e
the concentrated metal alkoxide test solutions were made up by weight.
A known weight of base was t i t r a t e d with standard acid for c a l i b r a t i o n
purposes, and test solutions were made up containing known weights of
stock base solution.
Results and Discussion
(a) 2-Methoxy-3,5-Dinitrobenzoic Acid
The parent i n methanol shows no absorption above 350 nm. As the
base concentration i s increased an orange species i s produced with
maxima at 364 nm and 488 nm ( f i g u r e 5.2). No change in spectral shape
was noted up to 2.3 M potassium methoxide, 2.5 M sodium methoxide or
2.5 M l i t h i u m methoxide, although the o p t i c a l densities increased w i t h
increasing base concentration. Hence only the 1:1 adduct (5.0) i s
formed at these base concentrations and there i s no evidence f o r 1:2
or 1:3 adduct formation
- 117 -
The data with potassium methoxide i n table 5.1 show that the
o p t i c a l density at 490 nm reaches a l i m i t i n g value of 0.61 at high base
concentrations and t h i s value i s taken to indicate complete conversion
to 1:1 adduct.
Equilibrium constants were calculated using equations 5.1 or 5.2.
The l a t t e r equation being used fo r the f i r s t seven rows where the indicator
concentration was increased.
The data with sodium methoxide were treated i n a similar manner,
and are i n table 5.2.
I t was not possible t o achieve complete conversion using l i t h i u m
methoxide and i n t h i s case a value corresponding t o t o t a l complex
formation with sodium methoxide was used t o calculate values of the
equilibrium constant ( t a b l e 5.3).
K _ °-D490 1
C 0.61 - O.D49Q [Base]
O.D "c K = 4 9 0 5.2
6-1 " O.D490 [Base] 490
The values with l i t h i u m methoxide indicate a value f o r K at low c
base concentrations of 0.02 ± .005 I mol - 1, The values increase with
increasing base concentration. The order at any p a r t i c u l a r base con
centration being:
NaOMe > KOMe > LiOMe. This contrasts w i t h the order of the
a c i d i t y function i n these basic media which decrease i n the 116
order: KOMe > NaOMe > LiOMe.
Two factors which are l i k e l y to be important i n increasing e q u i l i
brium constants for formation of adduct ( 5 . 0 ) with base concentration
are ( i ) a general increase i n ba s i c i t y of the medium and ( i i ) s p e c i f i c
association of the adduct with cations. I t i s d i f f i c u l t to separate
- 118 -
Table 5.1
Measurements of Equilibrium Constants and Acidity
Functions w i t h Varying Potassium Methoxide Concentration
(Parent i s 2-Methoxy-3,5-Dinitrobenzoic Acid) i n Methanol
at 25°C.
[KOMe]/M [Parent] 10 5 0 - D 4 9 0 K e q / J i
/M I mol 1
0 33.35 0.0 -
.0528 33.35 .01 .031 15.84
.074 33.35 .015 . 0322 16.01
.1057 33.35 .022 .034 16.18
.211 33.35 .07 .055 16.68
.317 33.35 .175 .093 17.09
.423 33.35 .30 .122 17.33
.52 3.32 .065 .23 17.69
.693 3.32 .133 .40 18.06
.924 3.32 .175 .435 18.22
1.097 3.32 .310 .941 18.63
1.271 3.32 .385 1.344 18.85
1.444 3.32 .490 2.825 19.23
1.617 3.32 .575 10.15 19.84
1.791 3.32 .61 -
2.253 3.32 .61
18.62 + log (O.D/6.1 - O.D)
18.62 + log (O.D/0.61 - O.D)
rows 2-7
- 119 -
Table 5.2
Measurements of Equilibrium Constants and J M Acidity
Function with Varying Sodium Methoxide Concentration
(Parent i s 2-Methoxy-3 5-Dinitrobenzoic Acid) in Methanol
at 25°C.
jNaoMej 10 5 [Parent] °-D490 Keq/e mol 1
M /M /M
0 32.27 0 -
.0497 32.72 0.023 .0761 16.20
.0661 32.72 0.028 .0697 16.28
.0994 32.72 0.048 .0797 16.52
.1988 32.72 .140 .118 16.99
.2982 32.72 .291 .168 17.32
.3976 32.72 .531 .239 17.60
.3976 33.03 .055 .249 17.62
.5964 3.303 .115 .389 17.98
.7952 3.303 .233 .776 18.41
.9691 3.303 .351 1.398 18.75
1.188 3.303 .449 2.345 19.07
1.401 3.303 .525 4.403 19.41
1.5838 3.303 .580 12.2 19.91
1.797 3.303 .600 33.4 20.4
1.979 3.303 .602 38.0
2.497 3.303 .515
2.741 3.303 ,605
2.970 3.303 .580
18.62 + log (O.D/6.1 - O.D)
18.62 + log (O.D/0.61 - O.D)
rows 2-8
- 120 -
Table 5.3
Measurements of Equilibrium Constants and Acidity Function
with varying Lithium Methoxide Concentration (Parent i s
2-Methoxy-3,5-Dinitrobenzoic Acid) i n Methanol at 25°C.
[LiCMe]
/M
10 5 [Parent] /M
°-D480 °-D490 Keq/S, mol ^ JM
0 32.12 0 - -
.1068 31.80 .020 - .0293 16.14
.1918 32.12 .030 - .0245 16.31
.311 32.12 .040 - .0202 16.44
.407 32.12 .055 - .0213 16.58
.815 32.12 .153 - .0299 17.03
.887 32.12 .168 - .0304 17.07
.904 30.28 .171 - .0318 17.08
1.218 3.228 .040 - .0566 17.47
1.421 3.228 .055 - .0683 17.62
1.624 3.228 .085 - .0976 17.83
1.827 3.228 .110 - .118 17.96
2.030 3.228 .146 - .1508 18.12
2.284 3.228 .223 - .245 18.38
2.439 3.102 .256 - .288 18.48
1.931 a 3.102 .590 .608 - 20.01
2.33a 3.102 .62 .625 -
2.728a 3.164 .623 .650 -
a. Using sodium Methoxide
M = 18.62 + log (O.D/6.1 - O.D) rows 2-8
J M = 18.62 + log (O.D/0.61 - O.D)
_ 121 _
these effects precisely. However i t i s shown i n figure 5.1 that with
sodium methoxide the J M function defined by equation 5.3 increases
much more rapidly than does the function. With potassium methoxide
there i s a smaller difference between the J., and H„ values while with M M
l i t h i u m methoxide the values are lower than are the values.
This may be taken to show the much stronger association of (5.0 )
with sodium ions than with potassium ions than with l i t h i u m ions.
J M = PCKKj^) + l°g10( [Adduct] / [Parent] ) 5.3
(b) 2,4,6-Trinitroanisole
The behaviour of 2,4,6-trinitroanisole i n concentrated sodium 92
methoxide solutions has previously been examined by Rochester. In
agreement with his work i t was found that the 1,1-dimethoxy adduct had
maxima at 412 nm (e 25,700 I mol - 1cm - 1) and 488 nm (e 17,670 9. mol _ 1cm _ 1)
( f i g u r e 5.3). With increasing base concentration the in t e n s i t y of the band at
lower wavelength decreased while that of the band at longer wave
length i n t e n s i f i e d . These changes corresponding to formation of a 1:2
adduct. In these solutions an isobestic point was observed at 440 nm.
The 1:3 adduct i s not expected t o absorb i n the v i s i b l e region since
a l l negative charges are localised on to nitro-groups.
Optical density measurements are i n table 5.4.
For the f i r s t three rows only 1:1 adduct i s present allowing the
extinction c o e f f i c i e n t s for t h i s species to be found. Up to 3.4 M base
an isobestic point i s observed at 440 nm in d i c a t i n g no formation of 1:3
adduct. I t was possible t o calculate a value f o r o p t i c a l density at
488 nm of 0.88 corresponding t o complete conversion to the 1:2 adduct.
Thus O.D4g8 = [ l : l ] 0.40 + [1:2] 0.88 5.4
_ 122a _
and i f [ l : i ] + [l:2] = m 5.5
Then [l : 2 ] = (O.D 4 8 g -0.4 m)/0.48 5.6
But since the 1:1 and 1:2 adducts show an isobestic point at 440 nm
. - . [l:3] = (0.31 - O.D 4 4 Q)/0.31 5.7
Also since the concentration of free parent i s n e g l i g i b l y small
[ l : l ] = 1 - ( [1:2] + [1:3] ) 5.8
Hence the r e l a t i v e concentrations of [ l : i ] , [l:2] and [ l : 3 ] adducts were
calculated, table 5.4.
Vi s i b l e spectra with Lithium methoxide showed no change i n spectral
shape, from that expected fo r the 1:1 adduct, up t o the highest base
concentration attainable (2.6 M).
(c) N,N-Dimethylpicramide
Here there i s evidence only fo r formation of 1:1 and 1:2 adducts
by base addition at unsubstituted r i n g positions. Since the value of the
equilibrium constant f o r formation of the 1:1 adduct i s not p a r t i c
u l a r l y high, unchanged parent i s present i n these solutions.
Note In tables 5.4 to 5.16 the equilibrium constants f o r
formation of adducts with 1:1, 1:2 and 1:3 stoichiometries are
defined as below i n terms of the stoichiometric metal alkoxide
con cent rat ions
\ . 1 = [1:1] /( [Parent] [MOMe])
K V 2 = [ l:2 ] / ( [ l : l][MDMe] ) K 1 - 3 = [l:3]/([l:2][MDMe] )
- 122
A study by v i s i b l e spectroscopy of the reaction in DM30 containing 54
sodium methoxide was reported while t h i s work was in progress. This
shows how in media r i c h i n DMSO i t i s possible to obtain spectra of 1:1
and 1:2 adducts separately. Spectra obtained with N,N-dimethylpicramide
are i n f i g . 5.4. However the equilibrium measurements with which the
present work i s concerned refer t o methanol as solvent. In methanol the
formation of 1:1 and 1:2 adducts i s not we l l separated so that v i s i b l e
spectra of these species are not d i r e c t l y obtainable. Because of
solvent effects i t i s t o be expected that some changes i n spectral shape
and ex t i n c t i o n c o e f f i c i e n t s w i l l occur on transfer from methanol to
DM30/methanol mixtures.
In methanol solutions containing only parent and 1:1 adduct show an
isobestic point at 360nm. From the data i n tables 5.5, 5.6 and 5.7 the
amounts of 1:2 species present are obtained by equations 5.9 and 5.10.
[ l : l ] = (0.33 - O.D 3 6 0)/(0.33 - 0.18) 5.9
for KOMe and NaOMe while f o r LiOMe equation 5.10 applies
[ l : 2 ] = (0.365 - O.D 3 6 Q)/(0.365 - 0.185) 5.10 52
There i s evidence from Gold and Rochester's published data and 54
from the spectral i n DIVBO/MeOH that e ( l : l ) at 480nm has the value
10,000 a mol _^cm -which gives an o p t i c a l density for complete conversion
of 0.3 units at the parent concentration used. Also the parent absorbs
0.013 at 480nm, table 5.6, while at
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- 124 -
480 nm, the 1:2 species, at high base concentrations, absorbs 0.033 in potassium methoxide case, 0.026 in sodium methoxide case and 0.035
in case of l i t h i u m methoxide. Accordingly, the following equations hold:
[ l : l ] = {0-D 4 g o - 0.03[l:2] - 0.013[Parent] }/0.3 5.11 " f o r KOMe, table 5.5"
[1:1] - -f°- D4 8 0 " 0.026[l:2] - 0.013[Parent] }/0.3 5.12
"for NaOMe, table 5.6"
[ l : l ] = (O.D 4 8 0 - 0.035[l:2] - 0.013[Parent] }/0.3 5.13 " f o r LiOMe, table 5.7"
For example, i n potassium methoxide case, fi n d i n g [ l : 2 ] from
equation 5.9, s u b s t i t u t i n g t h i s value i n equation 5.11, assuming [Parent]
= 0, t h i s gives an approximate value f o r [ l : l ] . From the above obtained
values of [ l : l ] and [ l : 2 ] , the amount of parent i s obtained by t h i s
equation:
[Parent] = 1-([1:1] + [1:2]) 5.14 Substituting t h i s obtained value of Parent i n equation 5.11 allows re
calculation of 1:1 . This i s done i t e r a t i v e l y f o r every concentration. The
same procedure i s carried through f o r sodium and l i t h i u m methoxides.
(d) l-(2^-Hydroxy ethoxy ) -2 ,4 ,6-trinitrobenzene
Even at d i l u t e base concentrations cyc l i s a t i o n to the spiro-adduct 58 rj _-.
w i l l be complete (K=1.8 x 10 I mol ) in water, and the value i n methanol
w i l l be around t h i s figure . When spiro and 1:2 adducts are present
there i s an isobestic point at 440 nm, as seen from spectral shapes
(f i g u r e 5.5) and from tables 5.8 and 5.9. The values of o p t i c a l density
at the isobestic point are 0.48 ( i n case of potassium methoxide), and
at 0.49 ( i n case of sodium methoxide), hence the following equations
apply
- 125 -
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- 127 -
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- 128 -
[1:3] = (0.48 - O.D 4 4 0)/0.48 5.15 "for potassium methoxide"
[ l : 3 ] = (0.49 - O.D 4 4 Q)/0.49 5.16
"for sodium methoxide"
The o p t i c a l d e n s i t i e s for complete conversion to spiro adduct are
0.71 and 0.52 at 414 and 480 nm, respectively, for potassium methoxide.
The values are 0.68 at 414 nm and 0.49 at 480 nm, for sodium methoxide.
Measurements with base concentration above 4M, where there i s l i t t l e
spiro adduct present, allow the spectra l shape of the 1:2 species to be
found with both potassium and sodium methoxide. The r a t i o of extinction
c o e f f i c i e n t s for 1:2 adduct at 480 and 414 nm i s equal to 5.0 ( i . e .
y/x = el:2 at 480 nm/el:2 at 414 nm = 5.0).
For potassium methoxide, the amount of 1:1 adduct present in
solution can be calculated from the following equations (where y/x =
5.0).
O.D 4 1 4 = [1:1] (0.71) + [l : 2 ] x 5.17
O.D 4 g 0 = [1:1] (0.52) + [l:2]y 5.18
Solving the equations leads to
[1:1] = (5 0.D 4 1 4 - O.D 4 g 0)/3.02 5.19
For sodium methoxide, the following equations (where y/x = 5.0)
enables calculation of the amount of 1:1 (equations 5.20 and 5.21).
O.D 4 1 4 = [1:1] (0.68) + [ l ; 2 ] x 5.20
O.D 4 8 Q = [1:1] (0.49) + [1:2] y 5.21
Solving equations 5.20 and 5.21 leads to equation 5.22
[1:1] = (5 O.D 4 1 4 - O.D 4 g 0)/2.9 5.22
The amount of [i: 2] adduct i s obtained by subtracting the sum o f [ l : l J a n d
[l:3]from 1.0 as described by equation 5.23
[l : 2 ] = 1 - ( [1:1] + [1:3] ) 5.23
- 129 -
With l i t h i u m methoxide, the spectrum of the spiro-adduct remained
unchanged up t o the highest base concentrations obtainable (2.6M).
(e) N^fethylpicramide
With t h i s substrate two possible modes of 1:1 in te rac t ions are
proton loss or base attack at the three pos i t ion (scheme 5 . 1 ) .
Me N
O N NO
H Me N
NO NO O N + OMe Me H
NO O N NO
H OMe
SCHEME 5.1
An assumption that i t i s necessary to make, i s tha t the f r ac t i ons
i o n i s i n g by these modes do not vary great ly wi th base concentration.
Hence the spectral shape of the product of 1:1 in te rac t ion i s assumed
to be independent of base concentration.
The products of 1:2 and 1:3 in te rac t ion are l i k e l y to be (5.2) and
(5.3) respect ively.
Me Me N N
O N NO NO Q»N H H H
MeO Me OMe NQ
( 5 . 2 ) ( 5.3)
- 130 -
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- 132 -
From tables 5.11 and 5.12 and from spectra l shapes, (see f i g u r e
5 .6) , the f o l l o w i n g assumptions are j u s t i f i e d .
( i ) [Parent] + [ l : l ] + [1:2] + [ l : 3 ] = 1 5.24
( i i ) For KOMe and NaQMe, [ l : l ] and [ l : 2 ] adducts show an isobest ic point
at 460 nm.
( i i i ) L i t t l e parent i s present when [Base] > 1M.
( i v ) L i t t l e [ l : 3 ] adduct i s present when [Base] < 1M.
1. With KOMe
Below 0.2 M of base, the f o l l o w i n g equation may hold (rows 1-8 i n
table 5.11).
[ l : l ] = ( ° - D
4 6 0 - 0.02)/0.42 5.25
At t h i s range of base concentration;
Parent] = 1- [ l : l ] 5.26
Since the parent absorbs 0.21 un i t s at 410 nm ( f o r [Basel < 0.2M), the
f o l l o w i n g equations may hold .
° - D 4 1 0 = [ P a r e n t ] ( ° - 2 1 ) + [ 1 : ^ 5 - 2 7
and O . D 4 9 Q = [ l : l ] y 5.28
x and y represent the ex t inc t ion c o e f f i c i e n t s f o r 1:1 adduct at
410 and 490 nm, respect ively . Subs t i tu t ing the values of [ l : l ] obtained
from equation 5.25 and values o f [parent j obtained from equation 5.26 i n
equations 5.27 and 5.28 gives values o f x and y l i s t e d i n table 5.10.
From table 5.10, average, x = 0.710 and average y = 0.280, and K^.^ ^
40 i mol~^. Above 1M base, assuming [Parent] = 0, the amount of 1:3
species can be evaluated by equation 5.29
[ l : 3 ] = (0.44 - O .D 4 6 Q ) / 0 .44 5.29
From table 5 .11, the f o l l o w i n g equations are appl icable .
0 - D 4 1 0 = [ 1 : 1 ] x + T 1 : 2 ] z + [ 1 : 3 ] 0 , 0 2 5 - 3 0
° - D 4 9 0 = + t 1 : 2 l W 5 - 3 1
- 133 -
where z and w are the ex t i nc t i on c o e f f i c i e n t s f o r 1:2 species at 410 and
490 nm, respect ively . Assuming w/z = 3 . 0 and since x and y are known
we can r e -wr i t e equations 5.30 and 5.31 as:
° - D 410 = [ l : l ] ( 0 - 7 1 J + [ 1 : 2 ] z + [ l : 3 ]0 .02 5.32
O . D 4 9 Q = [1 :1] (0.28) + 3 [ l : 2 ] z 5.33
Solving equations 5.32 and 5.33, and rearranging gives the f o l l o w i n g
equation, which was used to f i n d the amount of 1:1 adduct f o r rows 14-24
in table 5.11 (equation 5.34).
[1:1] = (3 O . D 4 1 Q - O . D 4 9 Q - 0.06 [ l : 3 ] ) / 1 . 8 5 5.34
At t h i s range of base concentration ([Base] > 1M), assuming [parent] = 0
the amount of 1:2 adduct i s obtained by equation 5.23.
For rows 9-13 ( i n tab le 5.11) from the d e f i n i t i o n of K^ .^ , the
f o l l o w i n g equation can be w r i t t e n
[Parent] = [ l : l ] /K^^Base ] 5.35
[ l : l ] i n equation 5.35 i s obtained from equation 5.34, p u t t i n g the term
[ l : 3 ] = 0, and since K^.^ ^ 40 l m o l - 1 , i t i s possible to f i n d the amount
of [Parent] , from equation 5.35, and [1 :2] from equation 5.36
[ l : 2 ] = 1 - ( [ 1 : 1 ] + [Parent]) (where [ l : 3 ] = 0) 5.36
Data and values are shown in table 5.11.
2. With NaOMe
The same procedure as f o r potassium methoxide i s carr ied out f o r
sodium methoxide. The amount o f 1:1 species i s obtained ( f o r rows
1-8 i n table 5.12) by equations 5.37 and 5.26, which holds in t h i s
range, where 1:3 = 0 .
1:1 = ( O . D 4 6 Q - O.O2)/0.44 5.37
From equations 5.27 and 5.28, x and y values are shown in table 5.10,
where, average x = 0.725 (absorption value f o r 1:1 adduct at 410 nm)
and average y = 0.295 (absorption value f o r 1:1 adduct at 490 nm).
- 134 -
Table 5.10
Absorbance values f o r 1:1 adducts ( Ind ica to r N_Methyl picramide w i t h metal methoxides) in methanol at 25°C.
[KOMe] X410 y490 [NaOMe] X410 y490 [LiOMe] \ l l 0 y470 /M /M /M
.010 .777 .336 .0103 .721 .302 .011 .644 .415
.020 .715 .276 .0205 .714 .278 .022 .695 .367
.0334 .79 .273 .0308 .735 .286 .275 .715 .37
.0446 .702 .280 .0411 .731 .293 .0385 .718 .393
.0669 .71 .286 .0616 .693 .296 .055 .70 .37
.0892 .73 .275 .0822 .751 .308 .077 .709 .361
.111 .71 .274 .103 .757 .285 .099 .697 .367
.223 .70 .299 .205 .72 .289 .192 .686 .36
Indica tor = 3 x 1 0 1
- 135 -
Above 1M base (rows 12-22 in table 5.12), 1:3 adduct i s found by-
equation 5.38.
[ l : 3 ] - (0.46 - O .D 4 6 Q ) / 0 .46 5.38
Subs t i tu t ing the values of x and y, and assuming w/z = 1.45 in equations
5.30 and 5.31 gives:
[1 :1 ] = (1.45 O . D 4 1 Q - O . D 4 g o - 0.029 [ l : 3] ) / 0 . 756 5.39
In t h i s range, where [Parent] = 0, amount of 1:2 adduct ([Base]
> 1M) i s calculated by equation 5.23. For rows 9-11 i n table 5.12,
[ l : l ] in equation 5.35 i s obtained from equation 5.39, where [ l : 3 ] = 0
since K^.^ ^ 30 I m o l - 1 ( t ab le 3.12). Accordingly [Parent] i s obtained
from equation 5.35, using these values to obtain [ l : 2 ] from equation 5.36.
3. With LiOMe
For runs 1-8 i n tab le 5.13, the f o l l o w i n g equations may hold
([Base] < 0.2 M), where [1:3] = [ l : 2 ] = 0
O . D 4 1 Q = [Parent] (0.21) + [ l : l ] x 5.40
° - D 4 7 o = 5 - 4 1
Solving both above equations f o r x and y gives x = 0.71 and y = 0.37
(x and y were defined above and values are shown i n table 5.10). An
isobest ic poin t at 450 nm which has an absorption of 0.48 i s observed
between 0.5 and 1.5 M base. Hence
O . D 4 5 Q = [Parent] (0.045) + ( [ l : l ] + [ l : 2 ] ) ( 0 . 4 8 ) 5.42
since [Parent] + [ l : l ] + [ l : 2 ] = 1.0 5.24
Subs t i tu t ing equation 5.24 i n 5.42 and rearranging, gives
[Parent] = (0.48 - O.D 4 5 ( ) ) /0 .435 5.43
(which applied f o r rows 1-8 i n table 5.13).
Above 1M base concentration, equations 5.30 and 5.44 hold
O . D 4 7 Q = [1:1]y + [1:2]w 5.44
assuming w/z = 3.0, and so lv ing equations 5.30and 5.44 gives ( f o r
[Base] > 1M)
- 136 -
[1:1] =(3 O . D 4 1 Q - O . D 4 7 0 - [1:3]0.06)/1.76 5.45 Above 1M base, [ l : 3 ] i s determined by equation 5.46
[ l : 3 ] = (0.48 - O . D 4 5 0 ) / 0 . 4 8 5.46
For rows 9-12 in table 5.13, ^ 33 £ m o l - 1 , using t h i s value w i t h
[ l : l ] obtained from equation 5.45, when [ l : 3 ] = 0, i n equation 5.35 to
get the parent 's amount. [ l ; 2 ] i s found by equation 5.36.
( f ) 2 , 4 , 6 - T r i n i t r o a n i l i n e (Picramide).
In the presence of sodium methoxide an absorption has been
observed around 398 nm (e = 28,000 I mol~ 1 cm~ 1 ). This absorption
increases w i t h increasing base concentration u n t i l (Base] > 1.6M,
when another absorption at 470 nm s t a r t s t o develop and the absorption
at 398 s t a r t s t o decrease. At high base concentrations (> 3M), there
was not any absorption i n the v i s i b l e region.
Again as w i t h N-methyl picramide, there are two p o s s i b i l i t i e s f o r
1:1 in t e rac t ion : base addit ion or proton abs t rac t ion . We assume that
the e f f i c i e n c y of these processes does not vary great ly wi th base con
centrat ion .
1 . With KOMe
Below 1M base, the amount of parent can be found by one of the
fo l l owing equations ( f rom table 5.14).
[Parent] = (0.93 - O .D 4 0 Q ) / 0 .69 5.47
o r [Parent] = (0.53 - O.D 4 4 Q ) /0 .455 5.48
in t h i s range of base concentrations, only the parent and 1:1 adduct
are present, hence the amount of 1:1 adduct i s obtained by
[1:1] = 1-[Parent] 5.49
Above 1M base, there i s l i t t l e parent present. From table 5.14,
the op t i c a l densi t ies f o r 1:1 adduct are 0.93 at 400 nm and 0.22 at
480 nm and i t i s known from v i s i b l e spectra and from table 5.14 that
the 1:2 adduct absorbs at 400 nm and at 480 nm. Estimating an absorption
- 137 -
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- 140 -
f o r 1:3 at 480 nm of 0.03, the fo l lowing equations apply:
O , D 4 0 0 = ° - 9 3 + [ 1 : 2 1 Z + [ 1 : 3 ] ° - 0 3 5 - 5 0
O . D 4 g 0 = [1:1] 0.33 + [ l : 2 ] w 5.51
Solving equations 5.50 and 5.51, assuming w = z gives [ l : l ] = ( O . D 4 0 Q -
O . D 4 g 0 - [ l : 3 ] 0.03)/0.71 5.52
whi le the amount o f 1:3 adduct can be estimated by equation 5.53 at
480 nm
[ l : 3 ] = (0.19 - O . D 4 g 0 ) / 0 . 1 9 5.53
The amount of 1:2 species i s found by equation 5.23.
2. With NaOMe
As mentioned before i n case of potassium methoxide in media
containing 1M base or less, there i s an equ i l ib r ium between parent and
1:1 complex, the amount of parent can be found by one of the below
equations
[Parent] = (0.52 - O . D 4 4 Q ) / ( 0 . 5 2 - 0.064) 5.54
or [Parent] = (0.87 - O .D 4 0 Q ) / 0 .62 5.55
Equation 5.49 i s applied i n t h i s range of concentrations to calculate
the amount of 1:1 species, where [ l : 2 ] = [ l : 3 ] = 0.
Above 1M base, both 1:2 and 1:3 adducts are present, 1:3 in methanol
as solvent.
Solving the equations 5.56 and 5.51, where w = z
° ' D 4 0 0 = [ 1 : 1 J 0 , 8 8 + [ 1 : 2 ] z + [ 1 : 3 ] ° - 0 3 5 - 5 6
gives [1 :1 ]=<O.D 4 0 0 - O . D 4 g Q - [ l :3 ]0 .03) /0 .66 5.57
The amount o f 1:3 intermediate i s obtained by equation 5.53, whi le
[ l : 2 ] i s obtained by equation 5.23. Data and resu l t s are shown in table
5.15.
- 141 -
3. With LiOMe
The amount o f parent i s determined s i m i l a r l y by one of the fo l l owing
equations below. Below 1M base, the amount o f 1:1 species i s found
by equation 5.49
[Parent] = (0.82 - O .D 4 0 ( ) ) /0 .58 5.58
or [Parent] = (0.48 - O.D 4 4 ( ) ) /0 .40 5.59
Above 1M, the assumption i s made that there i s l i t t l e 1:3 complex
( i . e . [ l : 3 ] = 0) so that the only species are 1:1 and 1:2 which absorb
at 400 nm and 480 nm. Solving equations 5.60 and 5.61 (assuming w = z,
z and w are the absorbances f o r 1:2 species at 400 and 480 nm, res
p e c t i v e l y ) .
O . D 4 0 0 = [1:1] 0.82 + | l : 2 | z 5.60
° - D 4 8 0 = 0 - 2 1 + [ 1 : 2 ] w 5 - 6 1
gives [1:1] = ( O . D 4 0 ( ) - O . D 4 g ( ) ) / 0 . 0 1 5.62
whi le [ l : 2 ] can be found by subtract ing [ l : l ] from 1 ( i . e . [ l : 2 ] =
1 - [ 1 : 1 ] ) .
- 142 -
9
bo O
in CD CD
CM C i CM I D
CO 0") C D C O CM H
19 co co eg g a>
O H r t
^ 8
O l - l r O • •
C O C M CT) l O X
X r H l ^ -
co C M m
CM
o C M o :^ ,~. i -co o cr. L-, x ^ ^- o r-- x
i r f 3
I o
o o o 8 CM CM CM
CO CO O O X
o 3
•a •a <
CM C O 00 CM 00 CM O
W -t->
M jr. • ° !r •H (1) rH S •H
Q
d
Q
d
d 9
CM CM CM o o i - i i n c M o t ^ i o c o m O r - i c o x o c r - t ^ r - c o C M C M r H r - - < , - . , - H , - i r H
rH C.
CM CO CO
oo cn o
o in
2 8 m m
rr c~. r H 00 rt CO CM CM
C O T O ^ O T r H CM f- i r H O
CO cn cn co v co o CM C D T C ^ c o r r a j r H C M r o o c c o ^ r c r j o r ^ c o
L n c o r - c - o o c o o o a - / c n a i o o o o c o r ^ t > i r ) T r
co r j co1 co* a
6
00 r--oo cn CM CM
T O I D
CM CM CM
•rr oo CM ( O CM CM
l O n O H
a
5 uo co oo C£ X O rH O O r n CM
00 CO 10 GO t - o
H X LQ O r - CO C D X O
8 & *~ T-l t>3 OJ -NJ CO n co n
8 3 co - r
- 143 -
8 CM S CM : M O X
•r is
O -< o • •
bo 0
o x x co ro co CD o in C D C D in
CM CM CD O O
T]I n a CM in in CM
CTl CO t - L O t-- in o in cr, i i O r- ! CM T C O C7J
•8 C i D O O O O O ' - ' L O C O T r C N
i i i i
CD t \ j C\) * T U") GQ
co n CN] ^ oo r i T f n
0) OS
X
O O O O O O O O O O O O r i i n ^ C O - ^ C D X I o o CM m t- x
co c c <ji < D *r a> C D
O O O O O O O O O O O i i C M C O C O C M C O r H O
5 i r C ^ - i l i n C O C O i i C M C M c o o i > r o Q C M T - i i n S co in C D t~ ~
CM i i in S oo X O O <7» G>
•o <
C I CD M C D C l N CO "cr C O CM r i r l
a5 ^ o . 1
i c-- x C D c n n O 01 65 X CM CM CM i n , 1
x o
in CM x o
a s C O 0^ CO C O
CM CM C O CO
X r- o O r - . in m
n 0> X in r H C M fH r-i
X L O C D O C D C M i n O O O
8 in m co co in C D
s n m co t - t -
in co co C D t- T x X x x g " i x o
* C O l—I r l
o •a
s •H
cS1
Q
d CM CM CM CM
C D C D C M
CD CD CM M M CO
n n in in in H io i n t^- o c n o o --. H co U) cTi iO « CM I D
H M W N N CM CM CO CO
- 144 -
CM
1*J
be o
CM t > CO 00
m i> co U0
co co T P CM m - H
i i
+-> • H
0) T3
O •r-i a o 0 • H +->
CD OS
0 -G - P
rH CO O rH «H
in CO
o • H CD - P
rH
• P
3
CO
-p § +-> CO
• H
0° m CM
- P
-p
CD •a • H
I -p
3
a1
- -p CO CD
• H • P • H
•8 O
• H +->
O T-t o • • TP r H
O
I
CM g r H
O r -O • TP r -
CM
o o TP
-p c CD
o 00 TP Q
d s s TP TP Q
d
o o TP
Q
d
o CO CO Q
d
I T
r-H o o CM TP CD r H CD t> CD CD CD CD m CD
rH r H r H r H r H r H r H r H
r H TP CO TP CD CM CO CD m 00 rH rH r H CM CM
CO CD o o m TP CO
CO i - l o CO CD t > m TP m m TP m m TP
m 00 i > CD CO
t > CD' c r H CO* CD r H TP in TP TP TP TP CO TP
CO o CM TP m in r H t> t> rH o o o o o o o o o o r H CM CM CO TP
CO r H CO CD CM CM TP t > CO CD TP 00 TP 00 CD r H t > TP CO TP CO CM CM od CO TP CO CD I N 00 00 CO CO o 00 l> O- CD m
r H
CO TP 00 CO CO m r H r H CO 00 CM CD r H o o O O O o CD in CO CO CM r H r H O o
m o TP CM 00 CO t> TP TP t> TP CO t> m I N r H CO TP CD o 00 r H r H CM CM r H m CO o o r H r H r H r H r H r H CM CM CM CM CM CM CM CO
CM t > t > TP O CO O 00 CO CO r H r H iQ !> CO CM CO TP ss r H CM TP CO t > t > TP CM CO TP TP CM CM CO CO TP TP TP TP TP TP TP TP TP TP TP
CO CO CO 00 CM r H t > m CO r H r H CM r H i> t > CO r H r H CO 00 r H TP 00 TH CNJ TP O o I > m •3* m CD CD CD O t- 00 00 t> t> CD CD
CO CO TP m CD TP CM cc TP CO CM CM TP 00 00 o S O CO 00 00 CD in m TP r H O TP t> t> CO CO CO CM CM CM CM CM CM CM CM CM CM CM CM
CO CD r H CO 00 m t> CO CO CD CO CO CO CD I N m CO r H r H CO m [> CO CO CO CO CO 00 00 O TP 00 O o o o O o r H CO CD CO TP CO CM CO TP
r H r H CM CM CM
m
m CM
oo m CO
m
CD m m
8
00 m CM
m i
T P o CO
II
o •P ci o
• H
G
- 145 -
Conclusions
The pub l i shed a c i d i t y sca les f o r a l k a l i meta l methoxide
116 s o l u t i o n s i n methanol show t h a t a t a g iven base concen t r a t i on the
b a s i c i t y decreases i n t h e o rder KOMe > NaOMe > LiOMe. Th i s o rde r has
70
been a t t r i b u t e d t o the g rea t e r d i s s o c i a t i o n o f potass ium
methoxide i o n p a i r s compared w i t h sodium methoxide o r l i t h i u m methoxide
i o n p a i r s . T h i s r e l i e s on the assumption t h a t the i n d i c a t o r s used,
s u b s t i t u t e d a n i l i n e s and diphenylajnines t do not assoc ia te s t r o n g l y i n
t h e i r a n i o n i c forms w i t h c a t i o n s .
The present data show t h a t f o r N , N - d i m e t h y l p ic ramide where
measurements were made a t on ly moderately concent ra ted base concen t r a t i ons
t h e values o f e q u i l i b r i u m constants decrease i n the r a t i o KOMe >
NaOMe > LiOMe. However, f o r most subs t r a t e s t h e graphs shown i n f i g u r e s
5.8 - 5.15 show t h a t values o f e q u i l i b r i u m constants f o r f o r m a t i o n o f
1:2 and 1:3 adducts are i n the o rde r NaOMe > KOMe > LiOMe. T h i s may be
taken as evidence t h a t 1:2 and 1:3 adducts a s soc ia t e more s t r o n g l y w i t h
sodium ions than they do w i t h potass ium i o n s . A p o s s i b l e r a t i o n a l i s a t i o n
f o r t h i s may be t h a t i n 1:2 and 1:3 adducts nega t ive charge tends t o be
l o c a l i s e d on n i t r o g r o u p s r a t h e r than d e l o c a l i s e d about the n i t . r o groups
and r i n g . There i s the p o s s i b l i t y t h a t sodium ions may assoc ia te
p a r t i c u l a r l y w e l l w i t h l o c a l i s e d nega t ive charges.
0 . o
;Na;
( 5 . 4 )
- 146 -
I t i s possible t o at tempt a s e m i - q u a n t i t a t i v e t r ea tment i n terms o f i o n - p a i r a s s o c i a t i o n cons tan ts as f o l l o w s .
Th i s t r e a t s f o r m a t i o n o f 1:2 adducts f r o m 1:1 adducts and meta l
a l k o x i d e .
1:1 + M + + M + + OMe"
K 1:1,M+
1 : 1 , M M , CMe"
'OMe"
1:2 + 2M
. K 1 : 2 , M +
1:2, M + + M +
i K 1 : 2 , ( M + ) .
1:2 ( M + ) ,
Scheme 5.2
The v i s i b l e spec t r a o f f r e e and i o n - p a i r e d species are u n l i k e l y t o be
very d i f f e r e n t . So t h a t the measured e q u i l i b r i u m constant K c can be
w r i t t e n i n the fo rm (equa t ions 5.63 and 5 .64)
K 5.63
K -c
[ l : 2 ] + [ 1 : 2 , M + ] + [ 1:2, ( M + ) 2 ]
( [ 1 : 1 ] + [ 1 : 1 ] , M + )[Base]
[ l : 2 ] ( l • K 1 : 2 M + [ M + ] + K 1 : 2 M + K 1 ; 2 i ( M + ) [ M f )
M ' 1 + K l : l , l f [ U l > [ B a s e ] where [Base] i s a measure o f the b a s i c i t y o f the medium i n c l u d i n g f r e e
and i o n - p a i r e d base.
I f K i s the e q u i l i b r i u m cons tan t i n t h e absence o f a s s o c i a t i o n o f
adducts w i t h c a t i o n s , equa t ion 5.65 w i l l app ly .
K = [ l : 2 ] / [ l : l ] [Base] 5.65
Then
K =
K ( 1 + K l : 2 , M + [ M + ] + K 1 : 2 , M + - K 1 : 2 ( M ^ J ^ f ) 5.66
1 + K 1 ; 1 [ M + ]
Increases w i t h i n c r e a s i n g base c o n c e n t r a t i o n i n the values o f K
i n d i c a t e t h a t
> 1 5.67
1 + K. 1:1 M
i m p l y i n g s t r o n g e r a s s o c i a t i o n o f 1:2 adducts than 1:1 adducts w i t h
c a t i o n s .
There i s evidence t h a t the a s soc i a t i on constants o f 1 , 1 - d i a l k o x y
42 125
adducts w i t h sodium and potass ium ions have r a t h e r s i m i l a r va lues '
Hence t h e g r e a t e r values observed f o r K c w i t h sodium methoxide than w i t h
potassium methoxide when c o n s i d e r i n g 1:2 adduct fo rma t ion i m p l i e s t h a t
1:2 adducts a ssoc ia te more s t r o n g l y w i t h sodium ions than w i t h
potassium i o n s .
A s i m i l a r argument r ega rd ing 1:3 adduct a l s o i n d i c a t e s t h a t they
assoc ia te more s t r o n g l y w i t h sodium than w i t h potassium i o n s .
I
30
i s Q B O O. D O
1
0 I B
/ / / 17 /
•a
/ / I t
'/IB
M D M b ] / M I . D
FIGURF 5.1
H ( f r o m r e f.116) and J . . ( t a b l e s 5»1»5.2 and 5»3 ) a c i d i t y f u n c t i o n M M
s c a l e s f o r a l k a l i - m e t a l m e t h o x i d e s i n m e t h a n o l , t h e i n d i c a t o r
u s e d t o d e t e r m i n e J i s , ? - m e t h o x y - 3 , 5 - d i n i t r o b e n z o i c a c i d i n
m e t h a n o l a t 25° » ^
9
e c
C3
5
o TO rH
X O c
r - l cvi o
J -—- c
•H £ o
o • H o CO C «
a> r—'•
£> d
O CP
-H • H c
C j
!£
«
>> v b X o o
-<:;
£ i 0)
cv
$-< X o Q
f i _c; +3
re: e U E
b E= a-
'H c
o t—'. ^ >
•t-i CO -p
*p un ^ *
A B S O R B A N C E
I
o 1—!* Cr.,1
!
F I G . 5 . 3 OCH 2
8 NO
3x10 M CD ~7 o n O
CD
2-088 M , o m
t l 3.341 M 5
CD
/ 1 A B A S E ^ K O M e
s v3
/ /
.2 \
4 0 0 5 0 0 6 0 0
W A V E L E N G T H ( n m ) U . V / V i s i b l e s p e c t r a f o r l , 3 , 5 - t r i n i t o a n i s o l e ( 3 . 2 X 10 M) w i t h p o t . ^ s l u m m e t h o x i d e , — _ 2 , 0 8 8 M . 3.3^1 M i n m e t h a n o l a t 25°.
9
HaOH
NO
f i g . 5L 4 \ >1 «
•
0 0
•
OS
\ rS
5 0
8 i
B A S E COSC. i
122x10 M 2-87x10 H C3Q>
I N
D M S O / METHANOL \ .2 a 5 5 /1 (V/ v \
8 ©
I A WAV L JUfom) E E N G
FIGURE 5 A
U . V / V i s i b l e s p e c t r a f o r N , N - d i m e t h y l n i c r a m i d e (3 X 1 0 5 M) w i t h
s o d i u m m e t h o x i d e ,1.7.2 X 1 0 3 M ( — . ) and 2.8? X 1 0 3 M( - )
i n D M S O / m e t h a n o l m i x t u r e ( 8 5 / 1 5 ) ( v / v ) a t ? ? .
FIG. 5.5 /
8 NO ON
NaOMe > CO O \
HQ
> I
/ i
/ i
t BASE CONC. •
1.01 M
3.5 M
5.13 M
.1
8 8 8 8 n rn CO 8 tf)
WAVELENGTH(nm)
U . V / V i s i b l e s p e c t r a f o r l - ( 2 - H y d r o x y e t h o x y ) - ? , '4 9 6 - t r i n i t r o b e n z e n *
( 2 . 8 X l b 5 M) and s o d i u m m e t h o x i d e a t 1 .01M( — ) . 3.5 M ( - — - - - )
,5.13 M ( ) i n m e t h a n o l a t 25°.
FIG. 5.6 9
\
8
\
\ > I TO I -£ L 6 \
5
•5 \
.4
3 BASE CONC
0 0 ® H •
2.44 M .2 4.07 M
.1
\ v 1
3 5 0 4 5 0 5 5 0 6 5 0
WAVELENGTH (nm)
FIGURE 5.6
U . V / V i s i b l e s o e c t r a f o r N - r n e t h y l ^ i c r a m i d e ( h.H x V? p o t a s s i u m m e t h o x i d e a t 0 . 0 8 M ( ) f ?mhh w (
( ) i n m e t h a n o l a t ?.<f
F I G . 5 .7 .8 ( a
.7
N H
2
NO
5 3x10 M
CD on
« .1 CD
350 400 t_ 500 i _
450 i 55,0 6 00 ,
m
( b ) .9 milium- 0,0 M
8 0.293 M CD
.7 0 0 0.896 M m
1.493 M " I \
1.941 M X
2841 M .3
V.
350 4 0 0 450 500 550 i— 600
1 WAVELENGTH (nm)
P T r 5.7
' / V i s i b l e s n e c t r a f o r TT p i c r a m i d e ( 3 x 10° M) w i t h s o d i u m
m e t h o x H * : a ) 0.0 M ,0.208 M , 0 . 8 9 S M . b ) 1.493 M ,1.<*1 M , ? . 8 4 l » i n m e t h a n o l a t ?5°
/
.0.1
-1.3
FIG. 5.8
"-0.5
NO? / 1 I
/ / /
/
/ /
/ /
t
0
/ /
/
J * ' /
/ /
/
/
6 /
/ /
.17 / (BASEl/M jl.Q 1-5 ,^2.0 2.5
J O 3.5
JFIGITRF. 5.8
FIG. 5.9
-1.2
8 Ho"
o
2
N f y ° 2
N0 2
0.8$
/
•0.6.' 6 /
fofr * 1 © a
^ *
"0.2
-0-0
02 _ i
OA 0 . 6 [ B A S E 1 / M 0 . 8 1.0 1.2
_ P I GU RE 5 . a
A p l o t o f L o g K , - v e r s u s b n s p c o n c p n t r a t i n n * w 5.5 ,5.6 and 5„7 . " °
•0.1
--0.1 FIG. 5.10
.0.3
h-0.5 NO-
kO-7
g
-.0.9
.1.1
•-1.5
2.5 3 Q [BASE] /M 3 5
4.0
FIGURE 5-10
A p l o t o f Log K-^.p v e r s u s b a s e c o n c e n t r a t i o n . D a t a a r e i n t a o l ^ ~ 5 . 8 and 5 . 9 ". "
0.3 FIG. 5.11
r
0.1 ON?TY?2
-0.1
•0.3
•.0.5 L3 O
0.7
K0.9
M-1
2 U J '
N02
i / i i
o • /
/
A ' '
/
o
[BASE1/M 2-0 2.5 / 3.0 3.5 ™_ I? 4.0 U.S
— — i '
FIGURE 5.11
A p l o t o f L o g K 1 > 3 v e r s u s b a s e c o n c e n t r a t i o n . D ^ t a ai 5 . 8 and 5.9 ,
1.0
FIG. 5.12 '0.8
h0.6
0 N T T ^ V N Q
0.4
0.2
O O
ro
•0.0 / ©
h.0.2 / /
/ /
/ '
/ '
0 - '
•M i t
i i
.0.6
°; 5 1.0 15 2.0 2 5
.FIGURE _ J_._12
A p l o t o f L o g K}_.2 v e r s u s b a s e c o n c e n t r a t i o n . D a t a a r e i n t a h l o r 5.11 f 5.1? a n d 5.13 .
•as
•06 FIG. 513
OA
02
0 2 N | ^ N 0 2
0 , /
0.0
13
o & /
/ /
--OA
/
•.06
-08 ' /
h-1.0
/ i / /
o' -1.2 A*
-1.4
1.5 * / ' (BASEJ/M / 20 2-5 30 3.5 4.0 4.5
FIGURE 5,13
A n l o t o f L o g K , 0 v e r s u s base c o n c e n t r a t i o n „ D a t a a r e i n J 1:3
t a b l - s 5 . 1 1 , 5.12 and 5 . 1 3 .
0.2
FIG. 5.14
0.0
h-0.2
-OA
.0.6 CM
8 i
.0.8
h-1.0
.1.2
-1.4
© / ®
NC^ / /
/ */
/
© i i
2.0 I BASE]/ M 2-5
#' i i
3.0 3.5 4.0
FIGURE 5.1k
A n l o t o f Log K-| j 2 versus base c o n c e n t r a t i o n t a b l e s S.lk ,5.15 and 5.16 ,
Data are i n
OA
1-02 FIG. 5.15
• 0.0
L0.2
NH 2 VfY°2 m2
kOA
o
/ /
/ /
.08
h-1-0 / ft?
-J.2 0 .
2.5 i
(8ASEJ/M 3.0 3.5 k.0
=FIGURF __5„15
A p l o t o f Log K 1 ; 3 versus "base c o n c e n t r a t i o n . Data are in 5.1b , 5.15 and 5^16 .
- 148 -
APPENDIX
a. Lectures and Seminars organised by the Department of Chemistry
during the period 1978-1981.
(* denotes those attended).
15th September 1978
Professor W. Siebert (University of Marburg, West Germany),
"Boron Heterocycles as Ligands i n Transition Metal Chemistry".
22nd September 1978
Professor T. Fehlner (University of Notre Dame, USA),
"Ferraboranes : Syntheses and Photochemistry".
12th December 1978
Professor C.J.M. S t i r l i n g (University of Bangor)
'"Parting i s such sweet sorrow' - the Leaving Group in Organic Reacti
14th February 1979
Professor B. Dunnell (University of B r i t i s h Columbia),
"The Application of NMR to the study of Motions i n Molecules".
16th February 1979
Dr. J. Tomkinson ( I n s t i t u t e of Laue-Langevin, Grenoble),
"Properties of Adsorbed Species".
14th March 1979
Dr. J.C. Walton (University of St. Andrews),
"Pentadienyl Radicals".
20th March 1979
Dr. A. Reiser (Kodak L t d . ) ,
"Polymer Photography and Mechanism of Cross-link Formation i n Solid
Polymer Matrices".
25th March 1979
Dr. S. Larsson (University of Uppsala),
"Some Aspects of Photoionisation Phenomena i n Inorganic Systems".
- 149 -
25th A p r i l 1979
Dr. C.R. Patrick (University of Birmingham),
"Chlorofluorocarbcais and Stratospheric Ozone : An Appraisal of the
Environmental Problem".
1st May 1979
Dr. G. Wyman (European Research Office, U.S. Army),
"Excited State Chemistry i n Indigoid Dyes".
2nd May 1979
Dr. J.D. Hobson (University of Birmingham),
"Nitrogen-centred Reactive Intermediates".
8th May 1979
Professor A. Schmidpeter ( I n s t i t u t e of Inorganic Chemistry, University
of Munich).
"Five-membered phosphorus Heterocycles Containing Dicoordinate
Phosphorus''.
9th May 1979
Dr. A.J. Kirby (University fo Cambridge),
"Structure and Reactivity i n Intramolecular and Enzymic Catalysis".
9th May 1979
Professor G. Maier (Latin-Giessen),
"Tetra-tert-butyltetrahedrane".
10th May 1979
Professor G. Allen, F.R.S. (Science Research Council),
"Neutron Scattering Studies of Polymers".
16th May 1979
Dr. J.F. Nixon (University of Sussex),
"Spectroscopic Studies on Phosphines and t h e i r Coordination Complexes".
23rd May 1979
Dr. B. Wakefield (University of Salford)
"Electron Transfer i n Reactions of Metals and OrganotiKtallic Compounds
- 150 -
23rd May 1979 Dr. B. Wakefield (University of Salford)
"Electron Transfer i n Reactions of Metals and Organometallic Compounds
with Polychloropyridine Derivatives".
13th June 1979
Dr. G. Heath (University of Edinburgh),
"Putting Electrochemistry i n t o Mothballs - (Redox Processes of Metal
Porphyrins and Phthalocyanines)".
14th June 1979
Professor I . Ugi (University of Munich),
"Synthetic Uses of Super Nucleophiles".
20th June 1979
Professor J.D. Corbett (Iowa State University, Ames, Iowa, USA),
" Z i n t l e Ions : Synthesis and Structure of Homo-polyatomic Anions of the
Post-Transition Elements".
27th June 1979
Dr. H. Fuess (University of Frankfurt),
"Study of Electron D i s t r i b u t i o n -in C r y s t a l l i n e Solids by X-ray and
Neutron D i f f r a c t i o n " .
21st November 1979
Dr. J. Muller (University of Bergen),
"Photochemical Reactions of Arrmonia".
28th November 1979
Dr. B. Cox (University of S t i r l i n g )
"Macrobicyclic Cryptate Complexes, Dynamics and S e l e c t i v i t y " .
5th December 1979
Dr. G.C. Eastmond (University of Liveprooi),
"Synthesis and Properties of Some Multicomponent Polymers".
- 151 -
12th December 1979 Dr. C.I. R a t c l i f f e (University of London),
"Rotor Motions i n Solids".
* 19th December 1979
Dr. K.E. Newman (University of Lausanne),
"High Pressure Multinuclear NMR in the Elucidation of the Mechanisms
of Fast, Simple Reactions".
30th January 1980
Dr. M.J. Barrow (University of Edinburgh),
"The Structures of Some Simple Inorganic Compounds of Si l i c o n and
Germanium - Pointers to Structural Trends in Group IV".
6th February 1980
Dr. J.M.E. Quirke (University of Durham),
"Degradation of Chlorophyll-a i n Sediments".
23rd A p r i l 1980
B. Grievson B.Sc, (University of Durham)
"Halogen Radiopharmaceuticals".
14th May 1980
Dr. R. Hutton (Waters Associates, USA),
"Recent Developments in Multi-milligram and Multi-gram Scale Preparative
High Performance Liquid Chromatography".
* 21st May 1980
Dr. T.W. Bentley (University of Swansea),
"Medium and Structural Effects i n S o l v o l y t i c Reactions".
10th July • 1980
Professor P. des Marteau (University of Heidelburg),
"New Developments i n Organonitrogen Fluorine Chemistry".
- 152 -
7th October 1980
Professor T. Felhner (Notre-Dame University, USA),
"Metalloboranes - Cages or Coordination Compounds?".
15th October 1980
Dr. R. Adler (University of B r i s t o l ) ,
"Doing Chemistry Inside Cages - Medium Ring B i c y c l i c Molecules".
12th November 1980
Dr. M. Gerloch (University of Cambridge),
"Magnetochemistry i s about Chemistry".
19th November 1980
Dr. T. G i l c h r i s t (University fo Liverpool),
"Nitroso Olefins as Synthetic Intermediates".
3rd December 1980
Dr. J.A. Connor (University of Manchester),
"Thermochemistry of Transition Metal Complexes".
18th December 1980
Dr. R. Evans (University of Brisbane, A u s t r a l i a ) ,
"Some Recent Comniunications to the Editor of the Australian Journal
of Failed Chemistry".
18th February 1981
Professor S.F.A. Kettl e (University of East Anglia),
"Variations i n the Molecular Dance at the Crystal B a l l " .
25th February 1981
Dr. K. Bowden (University of Sussex),
"The Transmission of Polar Effects of Substituents".
4th March 1981
Dr. S. Craddock (University of Edinburgh),
"Pseudo-Linear Pseudohalides".
- 153 -
11th March 1981 Dr. J.F. Stoddard ( I . C . I . Ltd./University of Sheffield),
"Stereochemical Principles i n the Design and Function of Synthetic
Molecular Receptors".
17th March 1981
Professor W. Jencks (Brandsis University, Massechusetts),
"When i s an Intermediate not an Intermediate?".
18th March 1981
Dr. P.J. Smith (Int e r n a t i o n a l Tin Research I n s t i t u t e ) ,
"Organotin Compounds - A Versatile Class of Organometallic Compounds".
9th A p r i l 1981
Dr. W.H. Meyer (RCA Zurich),
"Properties of Aligned Polyacetylene".
* 6th May 1981
Professor M. Szware, F.R.S.,
"Ions and Ion Pairs"
10th June 1981
Dr. J. Rose ( I . C . I . Plastics D i v i s i o n ) ,
"New Engineering Plastics".
17th June 1981
Dr. P. Moreau (Unviersity of Montpellier),
"Recent Results i n Perfluoroorganometallic Chemistry".
b. Conferences attended during the period 1978 - 1981
i. Annual Congress of the Chemical Society and the Royal I n s t i t u t e of
Chemistry, Durham University, A p r i l 1980.
- 154 -
c. F i r s t year induction course (October-November 1978)
A series of one hour presentations on the services available i n the
Department.
i . Departmental organisation.
i i . Safety matters.
i i i . E l e c t r i c a l appliances.
i v . Chromatography and microanalysis.
v. Library f a c i l i t i e s .
v i Atomic absorption and inorganic analysis.
v i i . Mass spectrometry.
v i i i . Nuclear magnetic resonance spectroscopy.
i x . Glassblowing technique.
- 155 -
References
1. Hepp, P., Ann., 215, 344, (1882).
2. Lobry de Bruyn, C.A., Rec. Trav. Chim. 9, 190, 208, (1890).
3. Lobry de Bruyn, C.A., and Ven Leent, F.H., Rec. Trav. Chim.,
14, 89, 150, (1895).
4. Jackson, C.L., and Boos, W.F., Amer. Chem. J., 20, 444, (1898).
5. Hantzsch, A., and Kissel, H., Ber., 32, 3137, (1899).
6. Van Leent, F.H., Rec. Trav. Chim., 15, 89, (1896).
7. Meyer, V., Ber., 27, 3153 (1894).
8. Meyer, V., Ber., 29, 848 (1896).
9. Jackson, C.L., and Gazzolo, F.H. , Amer.Chem. J., 23, 376, (1900).
10. Meisenheimer, J., Ann., 323, 205, (1902).
11. Crampton, M.R., Adv. Phys. Org. Chem., 7, 211, (1969).
12. P o l l i t , R.J., and Saudners, B.C., Proc. Chem. Soc., 176, (1962).
13. Buncel, E., and Symons, E.A., Canad. J. Chem., 44, 771, (1966).
14. Crampton, M.R., and Gold, V., J. Chem. Soc. (B), 498, (1966).
15. Buncel, E., Norris, A.R., and Russell, G.A., Quart. Rev. Chem. Soc.,
22, 123, (1968).
16. Russell, G.A., and Janzen, E.G., J. Am. Chem. Soc., 84, 4153, (1962).
17. Russell, G.A., and Janzen, E.G., J. Am. Chem. Soc., 89, 300, (1967).
18. Russell, G.A., Janzen, E.G., and Strom, E.T., J. Am. Chem. Soc.,
86, 1807, (1964).
19. Bunnett, J.F., Quart. Rev. Chem. Soc., 12, 1, (1958),
20. Bolton, R., "Organic Mechanisms", Penguin Education, (1972). Book .
21. M i l l e r , J., "Aromatic Nucleophilic Substitution", Elsevier, Sussex,
(1968), Book .
22. Bunnett, J.F., Zahler, R.E., Chem. Rev., 49, 273, (1951).
23. Ingold, J., "Structure and mechanism in organic chemistry",
Cornell Univ. Press, 306 (1953) Book .
- 156 -
24. Hughes, E.D. , Farad. Sec. Trans., 37, 603, (1941). 25. Crampton, M.R., Organic Reaction mechanisms, chap. 6., 9640, (1981).
26. Self, D.P., West, D.E., and S t i l l i n g s , M.R., J. Chem. Soc. ,
chem. cotmiun., 281, (1980).
27. Yokoyama, K., Nakagaki, R., Nakamura, J., Mutai, K. , and Nagakura, S.,
B u l l . Chem. Soc. Japan., 53, 2472 (1980).
28. Dalton, J.R., and Regan, S.L., J. Org. Chem., 44, 4443, (1979).
29. Bernasconi, C.F., Chimia., 34, 1, (1980).
30. Bunnett, J.F., Journal Chem. Educ., 36, 3, 278, (1961).
31. Bunnett, J.F., Connor, D.S., and O'Reilly, K.J., J. Org. Chem.,
44, 4197 (1979).
32. Strauss, M.J., Chem. Rev., 70, 6, 667, (1970).
33. Gan, L.H., and Norris, A.R., Canad. J. Chem., (1971), 49, 2490.
34. Cavazza, M., Morganti, G., Guerriero, A., and Pietra, F.,
Tetrahedron L e t t . , 21, 3703 (1980).
35. Crampton, M.R. , and Gold, V., J. Chem. Soc, 4293, (1964).
36. Foster, R., and Fyfe, C.A., Tetrahedron, 21, 3363 (1965).
37. Crampton, M.R., J. Chem. Soc. (B), 1208, (1968).
38. Foster, R., Fyfe, C.A., and Morris, J.W., Rec. Trav. Chim.,
84, 516, (1965).
39. Servis , K. L., J. Am. Chem. Soc., 87, 5495, (1965).
40. Barthel, J., Justice, J.C., and Wachter, R., Z. Phys. Chem.
(Frankfurt), 1973, 84, 113.
41. Al-A r u r i , A.D.A., and Crampton, M.R., J. Chem. Res., (S), 140,
(M) 2157, (1980).
42. Crampton, M.R., and Khan, H.A., J. Chem. Soc., Perkin I I , 2286,
(1972).
43. Al-Aruri, A.D.A., and Crampton, M.R. , J. Chem. Soc, Perkin I I ,
807 (1981).
- 157 -
44. Buncel, E., Norris, A.R., Russell, K.E., Sheridan, P., and Wilson, H., Canad. J. Chem., 52, 1750, (1974).
45. Cranpton, M.R., and Gold, V., Chem. Coromun., 549, (19660.
46. Crampton, M.R., and Gold, V., J.C.S(B), 893, (1966).
47. Byrne, W.E., Fendler, E.J., Fendler, J.H., and G r i f f i n , C.E.,
J. Org. Chem. , 32, 2506, (1967).
48. Gold, V., and Rochester, C.H. , J. Chem. Soc, 1722, (1964).
49. Crampton, M.R., and El-Ghariani, M., J.C.S., B, 330 (1969).
50. Abe, T., Nature, 187, 234, (1960).
51. Mariani, C., Modena, G., and Scorrano, G., J. Chem. Res., (S),
392, (1978), (M) 4601.
52. Gold, V., and Rochester, C.H., J. Chem. Soc., 1687, (1964).
53. Crampton, M.R., Gibson, B., and Matthews, R.S., Org. Magn. Rescm.,
13, 455, (1980).
54. Buncel, E., Hamaguchi, M., and Norris, A.R., Canad. J. Chem., 58,
1609, (1980).
55. Crampton, M.R., and Gibson, B., J. Chem. Soc. Perkin I I , 752,
(1980).
56. Gold, V., and Rochester, C.H., J. Chem. Soc., 1727, (1964).
57. de Rosi, R.H., Madoery, O.D., de Vargas, E.D., J. Org. Chem.,
45, 649, (1980).
58. Murto, J., Suom. Kemis t i l e h t i , B, 38, 255, (1965).
59. Knyazev, V.N., Drozd, V.N., and Mozhaeva, T.Ya, Zh. Org. Khim.,
16, 876 (1980); Chem. Abs., 93, 113468 (1980).
60. Foster, R., Fyfe, C.A., Emslie, P.H., and Foreman, M.I.,
Tetrahedron, 23, 227 (1967).
61. Fendler, J.H., Fendler, E.J., Bume, W.E., and G r i f f i n , C.E.,
J. Org. Chem., 33, 977, (1968).
62. I l l u m i n a t i , G., Adv. Hetrocyclic chem., 3, 285, (1964).
63. Fyfe, C.A., Tetrahedron Letters, 6, 659, (1968).
64. B i f f i n , M.E., Aust. J. Chem. Soc., 23, 963, 957 (1970).
- 158 -
65. B i f f i n , M.E., M i l l e r , J., Moritz, A.G., and Paul, D.B., Aust. J.
Chem. Soc., 22, 2561 (1969).
66. Arnone, C., Consiglio, G., Grorwitz, S., Matteson, B., Hornefeldt,
A.B., Noto, R., and S p i n e l l i , D. Chem. Sci., 13, 130, (1979).
67. I l l u m i n a t i , G., Doddi, G., and Stegel, F., Chem. Commun. 453,
(1969).
68. Newcombe, P.J., and Norris, R.K., Aust. J. Chem., 32, 1709,
2647 (1979).
69. Budyba, M.F., Terent'ev, P.B., and Kost, N.N., Vestn. Mosk. Univ.,
Ser. 2: Khim., 20, 358 (1979) Chem. Abs., 92, 75441 (1980).
70. Jones, J.R., "The ionisation of carbon Acids", Academic Press
(1973) Book .
71. Foster, R., and Fyfe, C.A., J. Chem. Soc. (B), 53, (1966).
72. Strauss, M.J., and Johanson, R.G., Chem. Ind., (London), 8, 242
(1969).
73. Janovsky, J.V., and Enb, L., Ber., 19, 2155, (1886).
74. Canback, T., Svensk. Farm. Tidskr., 48, 153, (1949).
75. Canback, T., Svensk. Farm. Tidskr., 53, 151, (1949).
76. G i t i s , S.S., and Kaminsbii, A.Y., J. Gen. Chem., U.S.S.R., 28,
1393, (1960).
77. Fyfe, C.A., Canad. J. Chem. Soc., 46, 3047, (1968).
78. Fendler, E.J., Fendler, J.H., Byrne, W.E., and G r i f f i n , C.E.,
J. Org. Chem., 33, 4141 (1968).
79. Fenfrow, R.A., Strauss, M.J., and Terrier, F., J. Org. Chem.
45, 471 (1980).
80. Foster, R., and Fyfe, C.A., Rev. Pure. Appl. Chem., 16, 61 (1966).
81. Crampton, M.R., and Gold, V., J. Chem. Soc. (B), 23, (1967).
82. Lewis, G.N., and Seaborg, G.T., J. Am. Chem. Soc., 62, 2122 (1940).
- 159 -
83. Clapp, L.B., Lacey, H., Beckwith, G.G., Strivastava, R.M., amd JMiamrad, N., J. Org. Chem., 33 , 4262, (1968).
84. Crampton, M.R., J. Chem. Soc. (B), 1341 (1967).
85. Norris, A.R., Canad. J. Chem. Soc., 45, 175, (1967).
86. Foster, R., and Fyfe, C., Farad. Soc. Trans., 61, 1626, (1965).
87. Fyfe, C.A., Foster, R., Chem. Corrmun. 1219, (1967).
88. B a l d i n i , G., Doddi, G., I l l u m i n a t i , G., and Stegel, F., J. Org. Chem.
41, 2153 (1976).
89. Chatrousse, A.P., Terr i e r , F., and Shaal, R., J. Chem. Res.
(S), 228, (M), 2413 (1977).
90. Hosoya, H. , Hosoya, S., and Nagukura, S., Theor. Chim. Acta.
12, 117, (1968).
91. Foster, R., and Mackie, R.K., Tetrahedron, 16, 119, (1961).
92. Rochester, C.H., J. Chem. Soc., 2404, (1965).
93. P o l l i t t , R.J. and Saunders, B.S., J. Chem. Soc., 1132, (1964).
94. Benesi, H.A., and Hildebrand, J.H., J. Am. Chem. Soc., 71, 2703
(1949).
95. Destro, R., Gramaccioli, C.M., and Simonetta, M., Acta Crystallogr.
B24, 1369 (1968).
96. Ueda, H., Sakabe, N., and Tanaka, J., B u l l . Chem. Soc. Jap.
41, 2866, (1968).
97. Destro, R., Gramaccioli, C.H., and Simonetta, M., Nature, 215,
389 (1967).
98. Gold, V., and Rochester, C.H., J. Chem. Soc., 1692, (1964).
99. Berasconi, C.F., J. Am. Chem. Soc., 90, 4982 (1968).
100. Fendler, H.J., Fendler, E.J., and G r i f f i n , C.E., J. Org. Chem.,
34, 689 (1969).
- 160 -
101. Fendler, E.J., Embsberger, W., and Fendler, J.H., J. Org. Chem. 35, 287 (1970).
102. Bernasconi, C.F., J. Am. Chem. Soc., 92, 4682, (1970).
103. Morrison, R., and Boyd, R. "Organic Chemistry", Chap. 1. Editors:
A l l y n and Bacon, 3rd Edition Book .
104. Schaal, R., and Teze, A., B u l l . Soc. Chim. France, 1783 (1961).
105. Larsen, J.W., Amin, K., Fendler, J.H., J. Am. Chem. Soc.
93, 2910 (1971).
106. Larsen, J.W., Amin, K., Ewing, S., and Magid, L.L., J. Org. Chem.
37, 3857 (1972).
107. Fendler, J.H., and J.W. Larsen, J. Org. Chem., 37, 2608 (1972).
108. Buncel, E., Norris, A.R., Proudlock, W., and Russell, K.E.,
Canad. J. Chem. Soc., 47, 4129 (1969).
109. Murto, J., "The Chemistry of hydroxyl group". Wiby-Interscience,
New York, 1087 (1971) Book .
110 Danil de Namur, A.F., J.C.S., Farady. v o l . 1. 2101 (1978).
111. B a r t o l i , G., and Todesco, P.E., Accounts Chem. Res., 10, 125,
(1977).
112. Parker, A.J., Proc. Chem. Soc. 371, (1961).
113. Hammett, L.P., and Deyrup, A.J., J. Amer. Chem. Soc., 54, 2721
(1932).
114. More O'Ferrall, R.A., and Ridd, J.H., J. Chem. Soc., 5030 (1963).
115. Stewart, R., O'Donnell, J.P., Cram, D.J., and Rickborn, B.,
Tetrahedron, 18, 917, (1962).
116. Rochester, C.H., "Acidity Functions", Academic Press, New York
(1970). Book
117. Gold, V., and Hawes, B.W.V., J. Chem. Soc., 2102 (1951).
118. Alder, R.W., Chalkley, G.R., and Whiting, M.C., Chem. Conm.,
405, (1966).
119. Rochester, C.H., Trans. Faraday Soc., 59, 2820 (1963).
- 161 -
120. Rochester, C.H., Quart. Rev., 20, 511, (1966). 121. Crampton, M.R., El-Ghariani, M.E., and Khan, H.A., J.C.S. Perkin I I
1178, (1972).
122. Davies, C.W., "Progress i n Reaction Kinetics," v o l . 1, 161, Editor :
Porter, Pergamon Press (1961).
123. Jones, J.R./'Progress in Reaction Kinetics ", v o l . 7, 1, Editor :
Jennings and Cundall (1975).
124. T e r r i e r , F., Ann. Chim., 4, 153, (1969).
125. Crampton, M.R., and Khan, H.A., J.C.S., Perkin I I , 1173 (1972).
126. Crampton, M.R., and Khan, H.A., J.C.S., Perkin I I , 1103 (1973).
127. Gold, V., and Toullec, J., J. Chem. Soc., Perkin I I , 596, (1979).
128. Crampton, M.R., J.C.S., Perkin I I , 2157 (1973).
129. Crampton, M.R., J.C.S., Perkin I I , 825, (1975).
130. Moir, M.E., and Norris, A.R., Canad. J. Chem., 58, No. 16, 1691,
(1980).
131. Buncel, E., Norris, A.R., Russell, K.E., and Wilson, H., Cand. J.
Chem., 52, 2306, (1974).
132. Destro, R., P i l a t i , T., and Simonetta, M., Acta. Crystallorgr.,
B35, 733, (1979).
133. Bernasconi, C.F., and Bergstrom, R.G., J. Org. Chem., 36, 1325,
(1971).
134. Buncel, E., Elvidge, J.A. , Jones, J.R., andWalkin, K.T. , J. Chem.
Res., (S), 272, (1980).
135. Mariani, C., Modena, G., Pizzo, G., and Scorrano, G., J.C.S ,
Perkin I I , 1187 (1979).
136. Crampton, M.R., J.C.S., Perkin I I , 1442, (1977).
137. Fyfe, C.A., Cocivera, M., and Damji, S.W., Accounts Chem. Res.
277, v o l . 11 (1978).
138. Bassani, A., Parto, M., Rampazzo, P., Quntily, U., and Scorrano, G.,
J. Org. Chem., 4 5 , 2263, (1980).
- 162 -
139. Cherkasov, V.M., Remennikov, G.Ya, Khim. Geterotsikl. Soedin, 239, (1980) Chem. Abs. 93, 25434, (1980).
140. Johnson, G.E., and Bowen, R.E., J. Am. Chem. Soc, 87, 1655,
(1965).
141. Qnys'ko, P.P., Gololobov, Yu. G. ( I n s t . Org. Khim., Kiev, U.S.S.R.
Zh. Qbschch. Khim (Russ.) 50(4), 729 (1980), Chetn. Abs. 93 :
94382 (1980).
142. Buneel, E., Norris, A,R., Elvidge, J. A., Jones, J.R, , and Walkin, K- T-> J- Chem. Res. (S), 326, (1980).
143. Cram, D.J., Rickborn, B., Kinglining, C.A., and Haberfield, P.,
J. Amer. Chem. Soc. 83, 3678 (1961).
144. Bethel, D., J. Chan. Soc., 666, Part I , (1963).
145. "Organic Solvents", 2nd Edition, v o l . V I I , Weissberger et a l . ,
(published : Interscience), Page 349, Book
146. Khan, H.A., Ph.D. Thesis, Chem. Dept., Univ. of Durham (1973).
147. Oilman, F., and Sane, S.M., Ber., 3734 (1911).
148. "Handbook of Chemistry and Physics", 57th Edition, CRC Press
(1976 - 1977).
149. Murto, J., and Tomnila, F., Acta Chem. Scand., 16, 63 (1962).
150. "Dictionary of Organic Compounds", 4th Edition, Eyre and Spottiswoode,
1964.
151. Beislstein Org. Chem., 6, 290.
152. Crampton, M.R., Gibson, B., and Gilmore, F., J.C.S., Perkin I I ,
91, (1979).
153. Wilson, M.J., Ph.D. thesis, Chem. Dept., Univ. of Durham (1975).
154. Blanksma, J.J., and Fohr, P.G., Rec. Trav. Chim. , 65, 711 (1946).
(155. Caldin, C.F., Crooks, J.E., and Queen A., J. Phys. E. (Sci.
I n s t r . ) , 6, 930 (1973).
156. Swinbourne, E.S,, "Analysis of Kinetic Data", Chap. 4., Nelson
Book.
- 163 -
157. Gan, L.H., and Norris, A.R., Canad. J . Chem., 52, IS (1974).
158. Gan, L.H., Aust. J . Chem., 28, 2403, (1975).
159. Cranpton, M.R., and Gibson, B., J. Chan. Soc., Perkin Trans. 2,
648, (1979).
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