DESIGN AND APPLICATIONS OF POLYMER-SUPPORTED

t-BUTYL HYPOHALITES

A s d e t a i l e d i n t h e previous chapter, t he use of

a funct ional ised insoluble polymer as a reagent o f f e r s

many p rac t i c a l advantages and unique s t r u c t u r a l environ-

ments f o r chemical reac t ions . S impl i f i ca t ion of t he

product work-up is the most important p r ac t i c a l advan+-

age. They provide a l s o the p o s s i b i l i t y of recycl ing and

automation and the f a c i l i t y of car ry ing ou t reac t ions

i n flow reactors on a commercial sca le . The polymer-

supported reagents may a l s o be used more conveniently

i n excess t o d r i v e react ions t o completion without

causing separa t ion problems. Scarce and/or expensive

mater ia ls can be e f f i c i e n t l y re ta ined when at tached t o

a polymer and, i f appropriate chemistry is avai lable ,

they can be recycled many t i m e s . The r e a c t i v i t y of an

uns table reagent may be a t tenuated when supported on

a crossl inked polymer matrix and the corros ive ac t ion

i n many cases can be minimised by t h i s type of

encapsulation. The t ox i c and malodorous materials can

be rendered environmentally more acceptable when

302 supported on an insoluble, non-volati le polymer support.

I n add i t ion t o these p r ac t i c a l advantages, a number

of po t en t i a l l y important r e a c t i v i t y changes may be

induced by t h e use of a funct ional ised polymer. When

t h e polymer is crosslinked, r e s t r i c t e d i n t e r ac t i on of

funct ional groups can be achieved. A high degree of

crossl inking, a low leve l of func t iona l i sa t ion , low

reac t ion temperatures and t h e o r i g i n of e l ec t ron i c

charges near the polymer backbone tend t o encourage

this s i t u a t i o n mimicking the i n f i n i t e d i l u t i o n condi-

t i o n i n so lu t ion . Under c e r t a i n conditions, it is

a l s o possible t o achieve t h e complimentary s t a t e of

high concentrat ion by heavi ly loading a polymer matr ix

w i t h one p a r t i c u l a r moiety. 92896 The se r ious drawbacks

associated with t h e crossl inked polymer-supported method

have a l s o been out l ined i n t he previous chapter. The

most se r ious drawback is the add i t iona l t i m e and c o s t

involved i n the synthes is of t h e crossl inked polymer-

supported reagent', The occurence of slow react ions and

poor y ie lds is a l s o a problem. ?he disadvantages may

w e l l be o f f s e t by t he po t en t i a l advantages, pa r t i cu l a r -

l y i n t h e case of regenerable and recyclable species

and i n t he case of r eg io and/or s t e r eose l ec t i ve reagents.

- Can these advantages of polymer-supported sol id-

phase reagents be rea l i zed i n t h e design and devel,

opment of crossl inked polymer-supported analogues

of t e r t i a r y hypohalites, which a r e s t r u c t u r a l l y

r e l a t ed t o t h e v e r s a t i l e syn the t i c reagent, t- butyl - .hypohaLites?

- I f s o t o what extent?

- How does t he r e a c t i v i t y of t h e hypohalite funct ion

depend on the s t r u c t u r a l f e a tu r e s of t he polymer

matrix?

-What a r e t he s p e c i f i c f ea tu r e s of t he polymer-

analogous react ions required f o r t he syn the t i c

design of the polymeric hypohalites?

- What is t he scope of t he polymeric hypochlorites

i n syn the t i c organic chemistry?

The work presented i n t h i s chapter is d i rec ted t o

address these i s sues . The s o l e i n t en t i on of these

s t ud i e s was not i n developing a super io r polymeric

reagent compared t o the low-molecular weight analogue,

but i n understanding t he fundamental f ea tu res of

polymer-analogous react ions and pol per-supported sol id-

phase general organic synthes is by taking t h e example

of t he design and development of polymer-supported sol id-

phase analogueof a t e r t i a r y hypohalite.

A. RESULTS AND DISCUSSION

1. Preparation and Characterization of Polymer-Supported

t-Hwohali t e s

The polymeric analogues of - t-butyl hypochlorite

and hypobromite were prepared by a three-step polyrner-

analogous reaction s t a r t i n g from 2% crosslinked styrene-

divinylbenzene c o p 0 1 y w ~ - The reaction sequence is

depicted i n Scheme 5. A ketone functional group,

CH 3-CO-CH 2-'

was introduced i n t o the polystyrene r e s in

beads (1) by Friedel-Crafts reaction with bromoacetone

using Lewis acid cata lys t . The reaction was followed

by the formation of an yellow-coloured der ivat ive

with 2,4-dinitropl~enylhydrazine reagent and an yellow

colouration when heated with iodine and a l k a l i (iodo-

form reaction), both reactions typ ica l of carbonyl com-

pounds w i t h a CHj-CD-functionality. The res in (2) - showed an intense carbonyl absorption a t 1725 cm-l i n

t he IR spectrum. This ketone function was then conver-

ted t o - t-alcoholic group by Grignard react ion with

methylmagnesium iodide followed by hydrolysis. A t this

s tage the absorption band a t 1725 cm-l disappeared

completely. No coloured p r d u c t s w e r e obtained i n its

reaction with iodine and a l k a l i and 2,4-dinitrophenyl-

hydrazine. The - t-alcohol r e s in was reacted with sodium

hypochlorite o r hypobromite t o ob ta in the polymer-

supported analogue of $-butyl hypochlorite (i) o r

hypobromite (5). The hypochlorite r e s in on treatment - w i t h iodine i n benzene yielded t h e hypoiodite r e s i n ( 6 ) . - The presence of chlorine, bromine .and iodine was detec-

ted q u a l i t a t i v e l y by t he Lassaigne's test and t h e i r

quan t i t a t i ve determination was ca r r i ed ou t by iodgnetric . - t i t r a t i o n and v e r i f i e d by t o t a l elemental analygig. .

Scheme . 5 : Preparation of Polymer - bound 1-Butyl Hypochlorite and tSutyl - H ypobromite

SCHEME 6. Preparat ion of _t-butyl hypoiodite res in .

The weight changes occurdng i n t he polymer-

analogous react ions gave an approximate ind ica t ion t o

the extent of func t iona l i sa t ion when t h e reactionswere

ca r r i ed out with gravimetric accuracy. The hypohalite

functions were estimated iodometrically. The ketonic

r e s in (2) had a capacity of 2.98 meq/g with respec t t o

t he CH3-CO-CH2- group corresponding t o 47.6'3 conversion.

When the react ion was conducted using polystyrene which ::

was not pre-awollen i n any solvent , t he capaci ty of the

resu l t ing ketone r e s in was only 1.63 meq CHFO-CH2- pe r

gram of the res in . T h i s corresponds t o only 26 .3%

conversion. The - t-alcohol r e s in (1) had a capaci ty of

2.86 meq/g with respect t o CH~.:C(OH) (Cki3) CH2- funct ion

corresponding t o almost complete conversion of t he k e t o

group t o 5-alcoholic group. This was a l s o evidenced by

t h e complete disappearence of t h e I R band a t 1725 c m ~ '

Here a l s o t.t~e e f f e c t of a s o l v e n t capable of swe l l i ng

t h e r e s i n was marked. When t h e r e a c t i o n was conducted . . i n abso lu t e d r y e t h e r , t h e e x t e n t of convers ion was

neg l ig ib l e . A mixture of THF and e t h e r gave better

r e s u l t s . Moreover, when a pre-swollen k e t o r e s l n was

used, t h e e x t e n t of convers ion was g r e a t e r . S i m i l a r was

t h e ca se w i t h t h e hypoha l i t e format ion s t e p . A pre-

swol len t - a l coho l i c r e s i n i n TW gave a reasonable e x t e n t - of conversion.

The hypoha l i t e f m c t i o n s were e s t ima ted

by t rea tment wi th a c i d i f i e d potassium i o d i d e and t i t r a t i n g

t h e l i b e r a t e d i o d i n e w i t h s t anda rd sodium t h i o s u l p h a t a

so lu t ion . The maximum a t t a i n a b l e c a p a c i t y f o r t h e hypo- . . c h l o r i t e and hypobromite r e s i n s was 2.33 meq/g and

1.43 m e d g r e spec t ive ly . When aqueous sodium hypoch lo r i t e

was used i n absence of THF, t h e c a p a c i t y ob ta ined was

on ly 0.56 meq Cl/g. Thus i t was p o s s i b l e t o o b t a i n r e s i n s

wi th d i f f e r e n t c a p a c i t i e s by . c o n t r o l l i n g r e a c t i o n cond-

i t ions , s e l e c t i o n of s u i t a b l e s o l v e n t s and d u r a t i o n Of

+act ions .

Po lys tyrene was selected as t h e suppor t f o r carry - i n g o u t t h e s e r e a c t i o n s because of i t s f avourab le phys i ca l

c h a r a c t e r i s tics and e a s e of f u n c t i o n a l i a a t i o n . Po lys ty rene

resembles to luene i n its e l e c t r o p h i l i c a romat ic s u b s t i t u -

t i o n r eac t ions . The f u n c t i o n a l group c a p a c i t y i n each of

the stages of the reaction sequence was found t o be i n

agreement with momuhst i tu t ion . Considering the steric

factors a t the two ortho positions, it can be reasonably

assumed tha t the subs t i tu t ion reactions took place prefer-

en t i a l ly i n the para position. This f a c t has been con-

firmed i n the case of chlorunethylation reaction of poly-

styrene using c13 NMR studies. 76

2. Role of Solvents i n the Extent of Functionaliaation i n the Pol ymer-Analogous Reactions

One major fac tor on which the degree of function.-

a l i sa tbn i n each reaction s t e p was dependent, Wa8 the

extent t o which polystyrene was swellable i n the d i f fe rent

solvents used i n the reactions. Solvents l i k e methylane :

chloride, chloroform, nitrobenzene and carbon d i su l f ide

were capable of swelling polystyrene t o a considerable

extent. Polystyrene was found t o swell maximum i n carbon

disulfide. , By absorbing considerable amount of solvent,

the crosslinked polymeric i.etwork can expand great ly and

become extremely porous forming apse@-gel. 3Q3 A t such

a low crosslink density as 2% the solvent.swollen poly-

mer may resemble a homogeneous solution, such t h a t the

gel network consists largely of solvent with only a small

f ract ion of the t o t a l mass being polymer backbone. Thus

the funct ional group capaci ty i n each of t he reac t ion

steps was found t o be dependent on t he nature of the

so lven t employed f o r the react ion. Thus i n t he Friadel-

Cra f t s reac t ion step, t he capaci ty of t he r e s i n (2 ) - with respect t o CH3-CO-CH2-group could be increased to

about 3-fold when t he s t a r t i n g r e s i n was allowed to

pre-swell i n carbonctlsulfide f o r about 12 hrs. Similarly.

the conversion of t he ke to group t o 5-alcoholic group by

Grignard react ion occurred more r ead i l y i n a THF-ether

solvent mixture than i n pure ether . I n t he case of pre-

swollen res in , t he reac t ion was more f a c i l i t a t e d . The

ex ten t of hypochlorite o r hypobraaite formation frcm the

t-alcohol r e s i n ( 3 ) was considerably enhanced when THT- - - water mixture was used as t h e so lven t ins tead of pure

water. These observations po in t t o t he r o l e of organic

solvents i n swelling the hydrophobic polystyrene mahjrix

and thereby permit t ing t he so lub le reac tan t s t o d i f f w e

i n t o t he crossl inked macromolecular matrix f o r e f f e c t i v e

reaction. The r a t e and ex ten t of reac t ions of a low-

molecular weight reagent with a funct ional group on t h e

polymer matrix was found t o be diffusion-control led, 304

which i n turn, dependea on t he p a r t i c l e s i z e of t h e

reac tan t molecules and the polymer beads, su r f ace area

of the beads and a c c e s s i b i l i t y i n t o the i n t e r i o r Of the

three-dimensional network by means of swelling.

3. Physical Nature and S t a b i l i t y of t he Polymer-

Supported Hypohalites

The polymer-supported hypohalite r es ins and t h e i r

precursors re ta ined the bead form c h a r a c t e r i s t i c s of

styrenedivinylbenzene copolymers prepared by suspension

copolymerization. 305 They were f i l t e r a b l e through

s in t e r ed g lass f i l t e r s . No considerable a t t r i t i o n was

caused t o t he polymers during the reac t ion s teps . On

conversion t o d i f f e r e n t funct ional groups, the colour

of the r e s in beads changed markedly. Incorporat ion of

t he keto funct ion changed t h e colour of t he o r ig ina l

polystyrene from colour less t o dark brown, the t-alcoho- - lit re s in was pink i n colour, t he hypochlorite reagent,

yellowish and t h e hypobromite reagent, reddish yellow

i n colour. The products of each s t e p of t he react ion,

sequence including t h e hypohali te reagents were s t a b l e

towards temperature and l i g h t . They were subjected t o

incubation a t d i f f e r e n t temperatures f o r d i f f e r e n t t i m e

in te rva l s . Upto 120°C, no p a r t i c u l a r e f f e c t was noticed.

Contrary t o t h e low-molecular weight hypohalites, the

polymeric reagents possessed much prolonged she l f l i f e .

Even a f t e r t h r ee years a f t e r preparing these reagents,

they r e t a i n t he o r ig ina l physical nature and chemical

r eac t iv i ty .

t-Butyl - hypochlorite, hypobramite and hypoiodites

were shown t o be v e r s a t i l e reagents ' used f o r car ry ing

out a v a s t number of syn the t i c reac t ions i n organic

chemistry.306 Theuse of these reagents under ordinary

conditions posed severa l problems. The prepara t ion of

these reagents was hazardous and explosion during the

preparation was repor tedP7 They have been found t o be

highly v o l a t i l e , very s e n s i t i v e t o temperature and

l i g h t , and have very s h o r t s h e l f - l i f e unless s t o r ed

a t l o w temperatures. 308

A s is the general case with heterogeneous react ions ,

t he d i f f e r e n t funct ional group conversions ca r r i ed on

polystyrene matrix never proceeded i n quan t i t a t i ve

yields. There ex i s ted t h e p o s s i b i l i t y of t he presence

of res idua l unreacted groups i n each step. But thcsk

unreacted groups never posed se r ious hurdles i n the

chemical r e a c t i v i t y of t h e f i n a l reagent. These groups

might have been inaccess ib le t o low-molecular weight

reagents during t he syn the t i c s t e p s as they were either

flanked by c ross l inks o r buried deep i n the i n t e r i o r

of t he macromolecular network. I t appears t h a t during

funct ional group conversions on the polymer matrix,

some conformational changes t ake place along t h e polymer

chain, addi t ional chain entanglement may occur, thereby

burying some f u n c t i o n a l groups deep i n s i d e t h e network,

which were once a c t i v e . Even i n presence of good

s o l v e n t s which a r e capable of s w e l l i n g t h e polymer

network considerably , t h e s e f u n c t i o n a l groups remained

r e l u c t a n t t o chentical t rans format ions . 24

4. Comparison of t h e Polymer-Analogous R e a a o n w i t h t h e Cow-Molecular Weiqht React ion

From the series of polymer-analogous r e a c t i o n s ,

it was found t h a t t h e procedure adopted wi th the pre-

swol len r e s i n us ing o rgan ic s o l v e n t s r inab le of s w e l l i n g

t h e polymer ma t r ix was t h e opt imal one which y i e l d e d

products wi th maximum f u n c t i o n a l group capac i ty . The

i n h e r e n t f e a t u r e s of polymer-aided r e a c t i o n s were

not iced i n t h e d i f f e r e n t s t a p e of t h e r e a c t i o n aequ@cm.

Most of t h e s e r e a c t i o n s were n o t s o s e n s i t i v e toward8

t h e r e a c t i o n cond i t i ons employed, mainly temperatura,

a s is t h e ca se w i t h low-molecular weight species.

Even i f t h e t e m y r a t u r e was s l i g h t l y r a i s e d t h a n the

usual range, no thermal decdmposit ion of t h e

r e a c t a n t s o r products was no t iced . Compared t o s i m i l a r

r e a c t i o n s w i t h low-mol x u l a r weight spec i e s , lesser

manual a t t e n t i o n was r equ i r ed f o r these r eac t ions .

Keactiops on t h e polymer ma t r ix r equ i r ed p r o l o ~ ~ g e d t i m e

f o r canple t ion . Thus when t h e Fr idel-Craf ts a l k y l a t i o n and

a c y l a t i o n r e a c t i o n s i n t h e homogeneous phase r equ i r ed

on ly one o r two hours f o r completion, t h e polymer-

analogous r e a c t i o n r equ i r ed s ix to e i g h t hours a t

r e f lux ing temperature of t h e s o l v e n t used. S i m i l a r

was t h e c a s e wi th the Grignard r e a c t i o n and hypoha l i t e

fonna t ion s t e p s . This has been a t t r i b u t e d t o t h e

r e l a t i v e i n a c c e s s i b i l i t y of t h e a c t i v e s i t e : ; on t h e

polymer backbone t o low-molecular weight reagents .

'The f u n c t i o n a l groups which a r e d i s t r i b u t e d a l l a long

t h e polymer backbone a r e n o t enough exposed and mobile

f o r e f f e c t i v e c o l l i s i o n wi,th o t h e r r e a g e n t molecules.

This n e c a s s i t a t - s t h e use of soma s o l v e n t s

which could s o l v a t e and expand t h e polymer netwo* 80

t h a t t h e a c t i v e sites a r e exposed t o t h e cont inuous

phase where they can r e a c t w i th o t h e r s u b s t r a t e s or : .

reagents . Even then t h e macroscopic i n s o l u b i l i t y Of

t h e s e immobilized r eagen t s n e c e s s i t a t e s g r e a t e r reac-

t i o n time and s e v e r e cond i t i ons . This clksadvdntage

is o f f s e t by t h e easy r e a c t i o n work-up. The work-up

of t h e r e a c t i o n mixture involves j u s t f i l t r a t i o n and

washing wi th d i f f e r e n t so lven t s . The p o s s i b i l i t y of

washing wi th d i f f e r e n t s o l v e n t s removes a l l t h e s o l u b l e

impur i t i e s , i nc lud ing s o l u b l e by-products and unreac ted

reagents . Thus h igh ly pure products could be obta ined . .

by t h i s technique.

8 8

5. Synthet ic Keactians of Polymer-Supported Hypohalites

Hypohalites have been widely used as a s t rong

oxidising reagent i n organic chemistry. 309 They wera

found t o oxidise alcohols 310 t o carbonyl canpounds and

su l f i de s t o su l f oxides. 311 The oxidations of alcohols

were repooted t o be taking p lace smoothly a t roan tam-

perature. But a t higher temperatures simultaneous

halogenation was a l s o found t o take place. The oxida-

t i o n of su l f i de s was found t o take place a t temperatures

as low as -7E°C. These react ions were ins tantdneow,

bu t t he separa t ion and i s o l a t i o n of the products from

the by-product, 2-butanol, a r e usual ly d i f f i c u l t . These

drawbacks of t he use of low-molecular weight hypohalites

could be overcane t o a g r ea t e r ex t en t by the use Of

polymer-supported analogues of these hypohalites. , . . .

The polymeric analogues of - t-butyl hypochlori te

and hypobromite w e r e used f o r t h e oxidat ion of alcohols,

&-halogenation of ketones and N-halogenation of amides (Scheme7)

Alcohols were oxidised t o corresponding carbonyl ccm-

pounds, primary t o aldehydes and secondary t o ketones,

i n 80-98% i s o l a b l e yields. The hypochlori te and hypo-

brmite reagents were capable of halogenating ketones t o

d-halc.derivaties and anrides t o N-hdo der iva t ives i n Ugh

yie lds . The hypoiodite reagent was used f o r the decarbo-

xyla t ion of aromatic and a l i p h a t i c carboxylic acids.

\F? U

-U-

. . IN

-r

a. Oxidation of Alcohols

Both primary and secondary alcohols were subjec ted

t o oxidat ion with the reagents. The d i f f e r e n t alcohols

which were oxidised using these reagents, the y i e l d

and conditionsof oxidat ion a r e presented i n Table 11~1.

The oxidation conditions involve s t i r r i n g of t he alcohol

with a 2-fold molar excess of t h e hypochlorite o r hypo-

bromite funct ion i n the r e s i n i n so lvents l i k e chloro-

form o r methylene ch lo r ide a t room temperature. The

work up of t he reac t ion mixture involves j u s t f i l t r a -

t i o n of t he spent res.ldue, washing w i t h so lvents and

removal of t h e so lven t from the f i l t r a t e and washings

t o af ford the oxidised product. Fran t he t ab le , it can

be seen t h a t the dura t ion required f o r t h e completl,qn

of t h e react ion is i n the range 40h i n c o n t r a s t

t o t h e co~nparat ively very s h o r t dura t ion necessary fo r

the low-molecular weight oxidations. This i s a con-

sequence of t he presence of the crossl inked hydrophobic

macromolecular matrix, and e f f e c t i v e low concentrat ion

of the reac t ive functlon. The polymeric reagent

functions as a r ese rvo i r of halogen and re leases them

slowly t o the react ion mixture as they a r e being

consum@ i n t h e course of t he react ion. The slow

r e l e a ~ e of a c t i ve furlctions gives S e l e c t i v i t y t o t he

reagent. Thus some e x t e n t of s u b s t r a t e s e l e c t i v i t y

was noticed w i t h t h e hypochlorlce and hypobranite

Table 111.1. Oxidat ion of Alcohols us ing Polymeric

Hypohali t8 heaaents

a 2-fold molar excess i n chloroform s o l v e n t a t room - temperature. _b Inc ludes pre-swel l ing a l s o

L

-

c Charac t e r i s ed by comparison w i t h a u t h e n t i c specimen. - d 2,4-DNP d e r i v a t i v e (70%). = 2,4-DNP d e r i v a t i v e (48%) - f Samicilrhazann (69%) -

t m m a l of a l - cohol

1.35

1.00

0.47

0.47

0.54

0.54

1.00

0.26

0.26

1.14

0.63

0.64

Alcohols

n - h t y l a lcohol

Benzyl a lcohol

Benzoin

Benzoin

Benz hydro1

Benzhydrol

Cyclohexenol

Cho le s t e ro l

Cho le s t e ro l

cis-1,2-Cyclo- hexanediol

Menthol

Borneo1

a R e s i a

- 4

- 4

- 4

- 5

- 4

- 5

- 4

4 - - 5

- 4

4 - - 4

~ i m e ~

40

42

40

42

40

44

42

44

44

42

43

40 . - -

productE

Butyraldehyde

Benzaldehyde

Benzi l

Benzi l

solated y i e l d

(%I 2

906

98%

86

83

Benzophenone 9 2

Benzophenone i , 87 I

Cyclohexanonc , 89

5 h -Cholesten- 9 8

5 one

one

I A-Cholesten-1 9 2 :

2-hydroxy Cy- 90 clohexanone

Menthone f

83-

Camphor 87

92 -

reagents . Simple a l i p h a t i c and aromat ic a l c o h o l s w e r e

o r i d i s e d wi th ease, s t e r o i d a l coho l s w i th complex

s t r u c t u r e s I lowed d i f f i c u l t y i n ox ida t ion .

(i) -- Haloqenation VJ Oxida t ion

With some subs t r a t e s , s imul taneous ha logena t ion

was a l s o found t o t a k e p l ace when t h e r e a c t i o n was

c a r r i e d o u t a t h igher temperatures . Thus o x i d a t i o n of

benzoin w i t - h t h e hypoch lo r i t e r e s i n a t temperatures

h ighe r than 45'C r e s u l t e d i n 2,2'-dichlorobenzil.

s l m i l a r l y with cyclohexanol, f -chlorocyclohexanone w a s

obtained. But wi th c h o l e s t e r o l , below a temperature

of 70°C, no c h l o r i n a t e d product was formed. A t temper-

a t u r e of 70-80°C, c h o l e s t e r o l gave t h e ch lo r ina -

4 t e d product, 6p-chl oro-a c h o l e s t e n e - h o n e (22) i d e n t i c a l

wi th t h e produc t obta ined by t h e ox ida t ion us ing t h e

lw-molecu la r weight analogues. but w i th t h e upp pot tad

hypoch lo r i t e reagent , a t empera tu re s below 70°C, t h e

5 product obta ined was A -tholes tenone. (27 ) . -

c h o l e s t e r o l

Scheme 8. Oxiudtiun of c h o l e s t e r ~ l a t low and

e l eva t ed tcrnk~.rc i ture~

The absence of c h l o r i n ~ ~ t i o n i n t h e c a s e of c h o l e s t e r o l

a t l& temperatures appears t o be due t o t h e steric

r e q u i r e ~ r ~ e ~ ~ t of t h e c r o s s l i n k e d mac rmolecu la r m a t r i x

r e l a t i v e t o t h e s o l u b l e r eagen t i n approaching t h e

r a t h ~ r r i g i d s t e r e i d s u b s t r a t e . I n t h e c a s e of t h e flex-

i b l e benzoin and cyclohexanol s u b s t r a t e s , such s teric

r e s t r i c t i o n s a r e comparat ively less and bo th o x i d a t i o n

and c h l o r i n a t i o n occur w i t h t h e polymer-supported

reagent as i n t h e low-molecular weight analogue a t

moderately low temperatures. Moreover, t h e r a t e of

oxida t ion r e a c t i o n s could be assumed t o be d i f f u s i o n -

c o n t r o l l e d and hence dependent on t h e s i z e of t h e

s u b s t r a t e .

(ii) Comparison wi th Lou-Molecular Weiqht Oxidan*

The o x i d a t i o n r e a c t i o n s w e r e c a r r i e d o u t i n

presence of a c e t i c a c i d and pyr id ine , i n a d d i t i o n to

the s o l v e n t used, i n analogy wi th t h e procedure adopted

wi th t h e low-molecular weight hypoha l i t es . 312 The

ox ida t ion r e a c t i o n s us ing most of t h e low-molecular

weight ox id i s ing r eagen t s a r e u s u a l l y c a r r i e d o u t i n

presence of e i t h e r some a c i d s l i k e s u l f u r i c a c i d or

a c e t i c a c i d o r bases l i k e p y r i d i n e o r t r i e t h y l d n e . 313

Thus wi th ct~rornum (VI) oxidants , 314 o x i d a t i o n of

a lcohols , which a r e n o t ac id - sens i t i ve , a r e conducted

i n presence of aqueous s u l f u r i c a c i d or a c e t i c a c i d i n

s to ichiometr ic proportions. I n t he case of acid-sen-

s i t i v e alcohols, oxidations w e r e found t o take p lace

e a s i l y i n presence of bases l i k e pyridine or t r i e t h y l -

amines. 3155 l6 Pyridinium chlorochromate and pyridinium

dichromate 317a318were used i n t he s e l e c t i v e ox ida t ionof

alcohols. Oxidations with dimethyl s ~ l f o x i d e ~ ' ~ a n d

N-lciromosuccinimide 320*32 'wore a l s o conducted i n presence

of pyridine o r triethylamine a s bases. I t was found

t h a t t h e funct ion of pyridine i s t o remove t he hydrogen

ha l ide formed as t he s a l t . Contrary t o these obser-

vations with the low-molecular weight oxidnts, 322-324

no rate-enhancement e f f e c t was noticed f o r t he use of

a c e t i c acid o r pyridine i n add i t ion t o t he reac t ion

solvent i n the case of t he newly synthesised polymer-

supported hypochlorite and hypobromite res ins . Such :

p a r a l l e l rate-enhancement of oxidat ion react ions w e r e

a l s o observed with polymer-supported i o n i c oxidants.

I n t h e case of ~ - b r o m o p o l y a c ~ ~ l a m i d e ~ ~ and polys tyr'ene

bound N-bromosul fonamide, 216 the react ions were f a c i l i -

t a t ed by the addi t ion of few'drops of d i 1 . H Z S 0 4 t o the

react ion mixture. H e r e the presence of s u l f u r i c ac id

reduced t h e t i m e required f o r completion of the reao t ton

t o two hours. S imi la r was the case with oxidis ing

reagents based on vinylpyridine polymers, l i k e

poly(viny1

pyridinium

pyridinj urn chlorochromate) , 219 poly (v inyl

dichrornate) 232 and poly(viny1 pyridinium hydro-

bromide/perbromide). 220 I n a l l these cases, t he oxidi-

s i n g funct ion is highly ac id i c and hence t h e presence

of sane ion i s ing medium f a c i l i t a t e s the reac t ion by

i on i c mechanism. Even though t he hypochlorite and

hypobromite funct ions a r e i o n i c i n nature, the presence

of highly hydrophobic polystyrene matrix reduces tho

overa l l hydrophi l ic i ty of t h e ac t i ve funct ions, thua

minimising the e f f e c t of i on i s ing medium on t he r a t e of

the reaction. However, the oxidat ion reac t ion can be

assumed t o toke place by an i o n i c mechanism r a t h e r

than a f r e e rad ica l mechanism. This was supported by

t h e f a c t t h a t t he addi t ion of free rad ica l i n i t i a t o r a

l i k e AIBN t o the reac t ion mixture during oxidat ion , :

react ions had no p a r t i c u l a r e f f e c t on the r a t e of t h e

reaction. The reac t ion may be proceeding by substi-

tu t i on of t he hydrogen on t he carbon bearing t h e

hydroxyl group followed by rapid l o s s of hydrogen

halide. This mechanism suggests t he p o s s i b i l i t y t h a t

ax i a l alcohols a r e oxidised more r ead i l y than their

equator ia l epimers due t o the more ready a c c e s s i b i l i t y

of the -C-H bond. This was es tab l i shed by t h e mono-oxi-

da t ion of cyclohexane-l,2-diol. The hydroxyl group

on the a x i a l pos i t ion was s e l e c t i v e l y oxidised giving

2-hydroxy cyclohexanone. The reason f o r a s luggish

react ion r a t e i n the polymer-supported react ion could

be ascribed t o the reduced f a c i l i t a t i o n of t he i o n i c

mechanism i n a highly hydrophobic environment.

(iii) Monitorina t h e Course of the Reaction

The oxidat ion react ions were followed by t h i n

l ayer chromatography on s i l i c a gel. Preparat ive t.1.c.

was used f o r t h e quan t i t a t i ve separa t ion of t he products.

The products obtained by evaporation of t h e so lven t wele

pur i f i ed by c r y s t a l l i s a t i o n o r d i s t i l l a t i o n . I n any

case, no product of over-oxidation was noticed con- ::

t ra ry t o the observation with most low molecular weight

oxidants l i k e p e r ~ n a n g a n a t e ~ ~ ~ am.i chromium (VI) 3 14

species . With these species , t he oxidat ion of primary

alcohols resu l t ed i n carboxylic ac ids and no t aldehydes.

But w i t h the polymeric hyprohalites, no carboxylic

acid formation was ohserved even with t he s imples t cases

of n-butyl alcohol o r benzyl alcohol. Even i f the

react ion was continued a f t e r complete conversion t o t h e

aldelyde f o r long dura t ion of t i m e , no f u r t h e r reac t ion

was observed t o take place a t room temperature. But a t

higher temperatues, w i t h s ubs t r a t e s having an oc -hydrogen

atom, halogenation was noticed. Thus, absence of

products of over-oxidation made the p roduc t4 so l a t i on

and pu r i f i c a t i on s t eps easy. Thus t he carbonyl

compounds were obtained by a simple f i l t r a t i o n followed

by washing t h e r e s i n t o e x t r a c t a l l t he product,

and f i n a l l y , evaporation of t he solvent . S imi la r

observation of t h e absence of any acids as products

i n t he oxidat ion of alcohols have been known i n t h e

case of oxidations using o ther polymer-supported oxidi- 94

s i n g reagents. The hypohalite oxidis ing reagents did

not show any s e l e c t i v i t y based on the nature of t h e

alcohol, whether the hydroxy group was at tached dire-

c t l y t o a r i n g s t r u c t u r e o r no t i n con t r a s t t o poly-

c4-vinyl pynidinium pennanganate) . 326 The polymer-sup-

ported pennanaganate was incapable of oxidis ing a lcohol ic

groups d i r e c t l y at tached t o r i ng s t r u c t u r e as i n cyolo;

hexanol, menthol, and cho les te ro l . b. .Haloqenations with t h e Polvmeric Hvpohalite Reagents

The - t-butyl hypochlorite and hypobranite r e s in s

w e r e found t o halogenate carbonyl compounds and amides

i n high yields. Carbonyl compounds w e r e converted t o

&-halogenated der iva t ives while antides w e r e converted

t o N-halogeno der ivat ives . Phthalimide, benzamide and

succinimide were observed t o undergo N-chlorination

on treatment with t he hypochlorite r e s i n i n 7 8 % , 82%

and 65% yie lds respect ively. The d e t a i l s of t h e halo-

genation react iom a r e presented i n Table 111. 2. The

react ion conditions involve ref luxing a s o l u t i o n of

t h e subs t r a t e (carbonyl compound o r amide) i n a s u i t a b l e

so lven t l i k e chloroform with a 2-fold molar excess of

t h e hypohalite reagent a t a temperature above 6 0 ° C

No halogenation react ion was found t o take place below

45OC. Simple ketones l i k e benzi l and cyclohexanone

underwent halogenation e a s i l y a t lower temperatures

w h i l e complex s t e r o i d ketones required high temperature

and long reac t ion periods. T h i s f a c t r e f l e c t s the

diffusion-control led penetrant t r anspo r t t o t he a c t i v e :

sites s i t u a t e d on the polymer backbone. Simple and

smaller molecules can mwe more f r e e l y i n t h e solvent-

swollen ge l network and g e t ready access t o t he a c t i v e

sites d i s t r i b u t e d i n t he ge l network.

Table IIL2.Haloqenation . - of Ketonns and Amides u s ina Polymeric

Hvpohal i te Resins ,

a - 2-f o ld molar excess i n c t ~ l o r o f o m so lven t . b - Includes pre-swell ing a l so . C - C h a r a c t e r i s :d by camparison with a u t h e n t i c specimens. d - Decomposed immediately.

I s o l a t e d Yield(%)

S u b s t r a t e

"

Acetophenone

E thylmethyl Ketone

Acetorlo

Cyclohexanone

Benzi l

Choles tenone

Phthal imide

Benzamide

Succinimide

~ e s i n ?

- 5 - 5

- 5

- 5

mmol of subs t -

r a t e

0.83

1.34

1.72

1.0

t i m e b ( h )

38

40

40

42

Temp ( O C )

- 4 I 0.47 49

42

44

44

42

productE

- 4

- 4

- 4

- 5

65

65

60

65

0.26

0.67

0.87

1.0

60

70

65

65

65

Phenacylbrornide

1-Bromo-2-buta- none

Uromoacetone d

2-Brmo cyclo- hexanone

68

54

N o t ; isola- ted

7 7

I

2,ZDichloro- b e n z i l

6-p-chloro- choles tenone

N-chloro phtha- . imide

N-~hlo&nzarnide

N-Bromo succ i - nimide

77

7 5

82

78

65

The work up of t h e r e a c t i o n mixture involved

j u l t f i l t r a t i o n of t h e r e a c t i o n mixture followed by

washing wi th d l££ e r e n t s o l v e n t s t o e x t r a c t t h e products

and f i n a l l y , removing t h e s o l v e n t by evaporat ion.

T h e p rodur t s were p u r i f i e d by r e c r y s t a l l i s a t i o n o r

f r a c t i o n a l d i s t i l l a t i o n . The r e a c t i o n was fol lowed

by t h i n l a y e r chranatography. As i n t h e c a s e of oxi-

d a t l o a r eac t ions , t h e p o s s i b i l i t y of f r e e r a d i c a l

mechanism can be e l imina t ed based on t h e f a c t t h a t

a d d i t i o n of rad l c a l i n i t i a t o r s has no rate-enhance--

ment ef f e r t i n t h e ha logena t ion r eac t ions . I n t h e

c a s e of subst ra l -es wi th-po ten t ia l s i t e s f o r K-halo-

genation, t h e te rmina l methyl was found t o be haloge-

nated p r e t e r e n t i a l l y . Thus i n t h e c a s e of e t h y l methyl

ketone, t h e bromination wi th t h e hypobromite r e s i n ,

yie lded 1-bromo-2-butanone and n o t 3-bromo-2-butanone.,

(i) Comparison with o t h e r Polymeric Haloqenatinq Reaaents

Both t h e hypocl .rori te and hypobrani te r eagen t s

were found t o be e f f i c i e n t i n c a r r y i n g o u t t h e halo-

gena t ion react ions i n c o n t r a s t t o s i m i l a r r eagen t s based

on polyacrylarnide and sulfonamide. N ~ h l o r o p o l y a c r y l a m i d e

and polystyrene-bound N-chlorosulfonamide were incapable

of e f f ec t i ng these react ions t o any s i g n i f i c a n t extent ,

probably due t o t he escape of ch lo r ine gas released

i n t o react ion medium during t h e course of t he reac t ion

under t h e experimental conditions ( 6 0 ° C ) . But with

t h e hypochlorite reagents, t h e r a t e of r e lease of

chlor ine was s o slow t h a t it was consumed by the

subs t r a t e instantaneously. This provides an add i t iona l

advantage of slow re lease mechanism. Moreover, t he

N-halogeno polyamide res ins w e r e incapable of carry-

i ng out N-halogenation of amide even though they showed

a g r ea t e r halogen-releasing capacity. With these

N-halogeno amides, presence of s u l f u r i c acid was nece-

s s a ry f o r e f f ec t i ve halogenation react ion t o occur.

But its presence has no e f f e c t on t he r e a c t i v i t y of

these hypohali t e res ins . Solvents l i k e chloroform

gave b e t t e r y ie lds with t he hypohalite reagents.

Branination of ketones with polymeric pyridinium hy-

drobromide/per bromide res ins nas been observed t o

t ake place smoothly i n methanol than i n chloroform

o r methylene chloride. 220 These observations g ive

some c lue t o the dependence of t he nature of t he

polymeric reagent on t h e so lven t used f o r the react ions.

(11) Reactions with t he Polymeric Hypoiodite Reagent

t-Butyl hypoiodite reagent has been found t o k -

Table 111.3. Reactions usinq Polymeric Hvpoiodite Resins

Substrate mmol m o l Product solated substrate reagent ield X 1

a - l i 2

Includes pre-swelling also ' in benzene) . 10h refluxing and 24h illumination in sunlight.

Phthalimide

Benzamide

Succinimide

Benzoic acid

Cyclohexane

carboxylic acid

0.67

0.83

1.00

0.82

0.78

2.1

2.7

3.0

2.6

2.36

4 2

48

5 2

34 ' i2

b 3 4-

70

70

70

60

60

N-iodophthalimide

N-iodobenzamide

N-iodosuccinimide

Iodobenzene

I odocyclohexane

5 8

6 2

5 4

5 2

67

capable of decarboxylating a l i p h a t i c as w e l l as

aromatic carboxylic acids and N-iodination of amides.

Thus benzoic acid and cyclohexane-carboxylic ac ids

were decarboxylated giving t he iodo de r iva t i ve when

i l luminated by sunl ight . The procedure was t o

i l luminate a mixture of t h e hypoiodite reagent and

the acid i n benzene t o d i r e c t sunl ight . The work-up

of t he reac t ion mixture was i d e n t i c a l t o t h a t followed

i n t he case of react ions wi th hypochlorite and hypo-

bromite res ins . The hypoiodite r e s i n converted benza-

mide, phthalimide and succinimide i n high y i e ld s t o

t he corresponding N-iodo chr ivat ive . The d e t a i l s Of

t he react ions a r e presented i n Table 111. 3 .

C. Recvclabi l i ty of the Spent Resin

One major considerat ion i n t he use of the

polymer-supported hypohali te reagents was the possi-

b i l i t y of recycl ing and reuse of t he spen t reagents.

The spen t polymeric reagents from the oxidat ion o r

halogenation step can be regenerated i n a s i n g l e s t e p

without any l o s s of a c t i v i t y for subsequent reac t iom.

The spent reagent can be f reed e f f e c t i v e l y from so lub le

reagents o r products by washing with d i f f e r e n t solvents.

The regeneration of t h e hypochloritm and hypobromite

reagents could be done by treiatrnent with :the' sodium hypo-

h a l i t e reagent i n THF-water mixture. The h y p o i d i t e

reagent was regenerated by t h e reac t ion of the spen t

r e s i n with sodium hypochlorite and iod ine i n benzene.

The capaci ty of t he r e s in can be varied i n t he regen-

e t a t i o n s t e p j u s t as i n t h e o r ig ina l synthes is of

hypohalite reagents. I n t h e present study, t he reage-

n t s were recycled upto f i v e t i m e s without appreciable

l o s s of reac t iv i ty . There was a s l i g h t and gradual

decrease i n t h e capaci ty of the resins. Af te r t h e

f i f t h r ecy l i s a t i on step some ex t en t of degradia t ion of

t he r e s in s was observed. The physical nature, f i l t e r a -

b i l i t y and swell ing c h a r a c t e r i s t i c s were found t o he

re ta ined under these recycl ing conditions. The change

i n the capaci ty of t he r e s in s i n the course of t h e

r ecy l i s a t i on steps a r e presented i n Table i IU .4 .

The only l o s s observed dur ing a l l these processes was

mechanical due t o powdering unavoidable i n the magnetic

s t i r r i n g process &due t o tl-e repeated t r ans f e r s Of t he

polymer samples .

Table 111.4 Heqer~er~.tion of the Hypochlorite Resin ( 4 )

Q Oxidation of benzoin t o benzil i n chlorofom solvent : :

a t room temperature. Yield noted a f t e r 4Oh, benzoin-

-to-reain ratio, la 2 i n a11 cases.

. Yo. of cycles

1

2

3

4

5 .

Capacity

2.32

2.30

2.17

2 .O

1.83

1 s o l a 4 y i e ld X

86

86

8 1

8 1

7 5

B . EXPERIMENTAL

General

The r e s i n support used was 2% crossl inked

styrene-divinylixnzene copolymer prepared by suspen-

s i o n copolymerization o r purchased from Fluka

(Switzerland). A l l t h e low-molecular weight compounds

used were commercially ava i l ab le samples pu r i f i ed by

d i s t i l l a t i o n o r c ry s t a l l i z a t i on , unless otherwise

s ta ted . Bromoacetone was prepared by bromination of

acetone following the l i t e r a t u r e procedure. 327 I*-

f r a r ed spec t ra was recorded on a Perkin-Elmer Spectro-

meter with K B r p e l l e t s , The solvents were a l s o

d i s t i l l e d before use.

1. Friedel-Craf ts Reaction of Bromoacetone with Cross-

l inked Polystyrene (a x Preparat ion of 2-C)rtopro~l

ges in (2)

Styrene-2% divinylbenzene . ( 200-400 m e s h )

beads w e r e thoroughly washed with benzene, methylene-

chlor ide and carbon t e t r ach lo r ide and d r i ed a t 100°C.

The r e s i n ( log) was suspended i n a mixture of carbon

disulfide-.methylene ch lo r ide (4: 1 v/v, 30ml) f o r 12h.

Bromoacetone (20g) and t he so lven t mixture (201111) was

taken i n a 500 m l round bottomed f l a s k f i t t e d with a

r e f l ux condenser and cooled i n an ice bath. Anhydrous

A1C13 (20g) was added i n small port ions over a period

of 15 min t o t h e bromoacetone with vigorous s t i r r i n g .

When the addi t ion was over, t he pre-swollen polymer

was added gradual ly t o the react ion mixture with

Occasional shaking and continuous s t i r r i n g . The mixture

was s t i r r e d a t room temperature f o r 15 min and heated

under r e f l ux f o r 6h. The reac t ion mixture was added

t o aqueous ethanol t o break t he L e w i s ac id complex.

The r e s in p a r t i c l e s w e r e co l l ec ted on a s i n t e r ed g l a s s

f i l t e r and washed with water,ethanol,and acetone,

(each, 10 m l x 3 t i m e s ) . The r e s i n was d r ied i n

vacuuo t o constant weight. Yields 12 .mg. CH3COCH2-

capaci ty of t he resin: 167 mg/g of the r e s in (2.98 mevg) . The r e s in gave an yellow coloura t ion when t r ea t ed

with iodine and a l k a l i and an yellow product with

2,4-dinitrophenylhydrazine reagent. I R spectrum ( K B r )

showed s t rong absorptions a t 1725 cm-I (C=O group) .

When the react ion was conducted with t he r e s i n

which was not pre-swollen under the same condit ions

as above, the capaci ty of t h e r e su l t i ng r e s i n was only

93 mg/g cprresponding t o 1.63 meq CH3COCH2- per gram

of res in .

2. Grignard Reaction of 2-Oxopropyl Resin (2) with

CH M q I : Preparation of t h e t-Alcohol Resin ( 2 ) -3

Magnesium turnings (24 5g) and a c r y s t a l of

iodine was suspended i n absolute d ry e the r (50ml) and

warmed gently. To t h e suspension, a so lu t ion of methyl

iodide (6ml) - i n dry e t h e r (30ml) was added i n small

quan t i t i e s s o t h a t gent le bo i l ing was maintained. When

a l l t h e magnesium was dissolved, t h e reac t ion mixture

was cooled i n i c e and t he suspension of t he pre-swollen

ke to r e s i n ( 2 ) - (2.98 meq/g: 89) i n tetrahydrofuran (50m1)

was added i n small port ions t o the methylmagnesium iod ide

formed,with constant s t i r r i n g . The reac t ion mixture

was heated under r e f l ux on a water bath f o r 6h. The

r e s i n was f i l t e r e d , washed with alcohol, cold d l 1 H2S04,

TW-water, THF, methanol and acetone and d r i ed i n

vacuuo t o constant weight. Yields 8.3839. The -- t-alcohol

r e s in (2) thus obtained showed no carbonyl absorption

i n t he I R spectrum. Capacity with respec t t o

-CH2C(CH3) 2-OH: 2.86 meq/g.

3. Treatment of the &-Alcohol Resin (3) with Sodium

tlypochlorite: Preparat ion of Polymer-Supported

A-Butyl hypochlori te (42

. The t-alcohol - r e s i n (2),(5g) was suspended i n

THF (30ml) f o r 12h. A 2M so lu t ion of f r e sh ly prepared

sodium hypochlorite (70ml) was added t o t h i s with

cooling i n an ice-bath and s t i r r i n g . The reac t ion

mixture was s t i r r e d a t room temperature f o r 24h.

The r e s in was f i l t e r e d , washed with water, THF,

methylene chloride, methanol and acetone and d r i ed

i n vacuuo t o colrtant weight. Yield 5.085gp, Analysis8

C 1 , 8 .3%~ capaci ty 2.33 meq ~ l / g .

4. Estimation of t h e Hypochlorite Function i n t he Resin(4)

The r e s in (100mg) was suspended i n 201111 of

g l a c i a l a c e t i c acid f o r 12h. The suspension was

warmed gent ly with lOml of 1 N H2S04 and l O m l of 10% K I

so lu t ion was added. The l i be r a t ed iodine was t i t r a t e d

aga ins t s tandard t h i o s u l f a t e so lu t ion using s t a r c h

ind ica to r . From the volume of t h e th iosu l f a t e consumed,

t h e equivalent of ava i l ab le ch lo r ine i n t h e r e s i n w a s

calculated.

Capacity of t he r e s i n obtained w i t h aqueous

NaOCl: 0.56 meq Cl/g.; capaci ty of t h e r e s i n obtained

i n t he treatment of t he t-alcohol - r e s in (pre-swollen

i n THF f o r 12h) with NaOCl i n aqueous THF: 2.33 meq. c~/G.

5. Preparat ion of Polymeric L-Butyl Hypobramite Resin(5)

The t-alcohol - r e s i n (l), (29) was t r ea t ed

with 2 M sodium hypobramite (501111) under identical

conditions a s above. Yield: 2.135g. Analysis: BX. 18.7% . The capaci ty of t he r e s i n was a l s o determined by the

iodometric procedure as described i n t h e case of

hypochlorite res in . Capacity: 2.33 meq. Br/g.

6. Preparat ion of Polvmeric H y ~ o i o d i t e Resin (6)

P 01 ymer-s upported - t-butyl hypochl o r i t e

res in , (4 ) , - (2g) was suspended i n benzene ( 10ml) f o r

12h. To the suspension was added, resublimed iodine

c r y s t a l s (5g) and s t i r r e d a t room temperature f o r 24h.

Af ter react ion, t he mixture was f i l t e r e d , washed with '

benzene, toluene, chloroform, methanol and acetone

and d r ied i n vacuuo t o constant weight. Yield: 2.201g.

Analysis; iodine, 28.25%; capaci ty of t he resin: 2.24 meq/g.

7. Estimation of Iodine i n t h e Hvpoiodite Resin ( 6 )

Polymer-supported hypoiodite r e s in (5) , ( 100mg)

was suspended is g l a c i a l a c e t i c acid, ( 2 O m l ) f o r 12h.

The suspension was gent ly warmed with 1NH2S04 (10ml).

The l i be r a t ed iodine was t i t r a t e d agains t s tandard th io-

s u l f a t e so lu t ion using s t a r c h indica tor . Capacity of

111

t h e resin: 2.24 meq I/g.

8. Oxidation of Alcohols with t h e Hypohalite Resins:

General Procedure

The alcohol (100mg) dissolved i n chloroform

(20ml) was s t i r r e d with a 2-fold molar excess of t he

polymeric t-butyl - hypohalites . The reac t ion was

followed by t h i n l ayer chromatography. Af te r t he

completion of the react ion, t he r e s in was f i l t e r e d and

washed with chloroform. The combined f i l t r a t e and

washings on evaporation of the solvent afforded t h e

corresponding carbonyl compounds. The d e t a i l s of

individual oxidations a r e presented i n Table 111. 1. The

~ r o d u c t s were i d e n t i f i e d and character ised by com-

parison (m.p/b.p and IR) with authent ic specimens.

9. &-Halogenation of Ketones and N-Haloqenation of A m i d e s :

General Procedure

The experimental procedure followed was

exact1 y analogous t o t he Oxidation procedures except

t h a t the temperature of t h e reac t ion was 60°C. The

d e t a i l s of the individual reac t ions a r e presented i n

Table 111. 2.

10. Decarboxylation Reactions usinq t h e Hypoiodite Resin

The caliDxylic acid (100mg) was heated under

r e f l ux i n benzene solvent f o r 10h. The reac t ion

mixture was cooled and :qas exposed t o d i r e c t sun l igh t

f o r 24h. Af te r the react ion, t he mixture was f i l -

tered, washed with benzene and the solvent was

removed by evaporation t o af ford t h e iodo compound.

The d e t a i l s of t he react ions a r e presented i n Table 111.3.

11. Recycling of the Spent Hypohalite Resins

The spent hypochlorite r e s i n (3g) from d i f f e r e n t

oxidation react ions was washed successively with

chloroform, methylene chloride, THF, methanol and

acetone, (201111 each, 3 t i m e s ) and d r ied i n vacuum..

The d r ied r e s i n was suspended i n THF f o r 12h. This

was t r ea t ed with f r e sh ly prepared 2 M so lu t ion of

Sodium hypochlorite reagent (50ml) as described e a r l i e r .

The regenerated r e s in was found t o have 2.30 meq Cl/g.

The spent hypobromite and hypoiodite resin.@

were a l s o regenerated analogously.