CHEMICAL ELEMENTS AND THEIR COMPOUNDS B Y N . V. SIDGWICK FELLOW OF LINCOLN COLLEGE HON. STUDENT OE CHBIST OHCTBOH FOBMEELY PROFESSOR OF CHEMISTRY IN THE UNIVERSITY OF OXFORD VOLUME II OXFORD AT THE CLARENDON PRESS
N . V. S I D G W I C K
F EL L O W O F LI N C OL N C O LL E G E
HON. STUDENT OE CHBIST OHCTBOH
F O B M E E L Y P R O F E S S O R O F C H E M I S T R Y
I N T H E U N I V E R S I T Y O F O X F O R D
VOLUME II
O X F O R D
Oxford University Press, Amen House, London E.C. 4
G L A S G O W N E W Y O R B: T O R O N T O M E L B O U R N E
W E L L I N G T O N
B O M B A Y O AL OT TT TA M A D K A S C A P E T O W N
Geoffrey Cuniberlege, Publisher to the University
I
1
Roprinted lithographically In
PJlMiI ,
G ro up VI 855
O X Y G E N (856). Ozone (859). Water (863). Hydrogen
Peroxide and
its Derivatives (868).
S U L P H U B ( 8 7 5 ) . Hydrogen Sulphides (878). Organic
Sulphides (880).
N itrogen Sulphides (892). Oxides of Sulp hur (894). Ox y-acids
of
Sulp hur (904). Organic Deriv ativ es of Oxides an d Oxy -acids
(921).
Oxy-halides (928). Thionic Acids (940). Sulp hur Halid es
(943).
SELENIUM, TELLURIUM, POLONIUM (948). Hydrides (951).
Organic
Derivatives of Selenium (953): of Tellurium (964). Oxides of S
elenium
(970):
Oxy -acids of Selenium (972). Oxides an d Ox y-acids of
Tel
lurium (980). Selenium Halides (986). Tellurium Halides
(990).
POLONIUM (995).
G r o u p V I A . C h r o m i u m , M o l y b d e n u m , T u n g s
t e n , U r a n i u m a n d
t h e U r a n i d e s . . . . . . . 998
CHROMIUM (1000). Hexavalent Chromium (1003). Penta- and
Tetra-
valent Chromium (1008). Trivalent Chromium (1009). Chromic
Com
plexes (1014). D iva len t Chromium (1022). Chromium Carbonyl
(1026).
MOLYBDENUM and T U N G S T E N (1028).
Hexavalent Compounds
(1032). H alide s (1033). Oxides (1037). Oxy -acids (1038). Pe nta
va len t
Com pound s (1047). T etr av ale nt (1053). Lower Valencies
(1057).
Carbonyls (1066).
U B A N I U M (1069). Hexavalent (1071): Tetravalent (1080):
Tri- and
Divalent (1085). N uclear Fission (1087). Properties of the 'U ra
ni oV
Elements (1091). Chemistry of N E P T U N I U M
(1093), PLUTONIUM (1094),
AMBEIOIUM (1095), and CURIUM (1096).
G r o u p V I I B . T H E H A L O G E N S . . . . .
1097
F L U O R I N E (1099). Hydrogen Fluoride (1102). Inorganic
Fluorides
(1112). Organ ic Flu orin e Com poun ds (1116). Oxides of Fluorin
e
(1185).
C H L O R I N E , B R O M I N E , I O D I N E (1139). Inte
r-ha log en Com pounds (1146).
Hyd rogen Halides (1160). Bi nary Halide s (1170). Organic
Com
pounds of Chlorine, Bromine, and Iodine (1174). Formation
(1174):
Miysioal an d Chemical Prop erties (1184). Perha lides M[X
n
] (1190).
Halogen Oxides (1201). Oxy -acids (1212). Com pounds of Po lyva
lent
Halogens (1243).
A S T A T I N E , N O . 85 (1260).
Group V I I A . . , . . . 1262
MAMCUNESB (1264); Heptavalent (1266): Hexavalent (1269);
Tetra-
ttlmt (1271): Tr iva len t (1274); D iva len t (1282). N
itrosy l Com-
|§undi (1288), T E C H N E T I U M , N o. 43
(1289). R H E N I U M (1291): Hepta-
|§undi (1288), N o. 43 (1289). (1291): Hepta-
¥i l tnt
C O N T E N T S
G r o u p V I IL I r o n , C o b a l t , N ic k e l . . . . .
1316
IROJST (1319). Fe rrous Com pounds (1327): Complexes (1335).
Fe rric
Compounds (1348): Complexes (1358). Carbonyls (1369).
Nitrosyls
(1372).
COBALT (1375). B iva len t (1376): Triva lent (1392).
Cobaltio Com
plexes (1396). Te trav ale nt Cobalt (1420). Carbonyls (1422). N
itro
syls (1423).
N I C K E L (1426). Non-valent and Monovalent (1429).
Divalent
(1430). Divalent Complexes (1438). Trivalent Nickel (1449).
Car
bonyls (1451). Nitrosyls (1452).
T h e P l a t i n u m M e ta l s . . . . . 1454
G r o u p V I I I A . R u t h e n i u m a n d O s m i u m . . . .
1455
Valencies (1455). R U T H E N I U M (1459): Divalent
(1460): Trivalent
(1465): Tetravalent (1475): Penta- (1478), Hexa- (1479), and
Hepta-
valent (1480): Octovalent (1481). Carbonyls (1482). Nitrosyls
(1484).
OSMIUM (1490). D ivalen t (1490): Triv alen t (1492): Tetra
va len t
(1493): H ex av ale nt (1499): Oc tovalent (1503). Carbonyls
(1509).
Nitrosyls (1510).
G r o u p V I I I B . R h o d i u m a n d I r i d i u m . . . 1 5 1
1
RHODIUM (1513). Divalent (1515): Trivalent (1516).
Complexes
(1520). Higher Valencies (1527). Carbonyls (1528).
IRIDIUM (1530). Divalent (1531): Trivalent (1532).
Complexes
(1535). Te trav ale nt (1541). Complexes (1544). H ex av ale
nt (1546).
Carbonyls (1548).
G r o u p V I I I C . P a l l a d i u m a n d P l a t i n u m . . .
. 1550
PALLADIUM (1553). D ivalent (1558). Com plexes (1561). Tr iva
len t
(1878): Totravalent (1574). Complexes (1575). Carbonyls
(1577).
Nitrosyls (Wl).
fummu
(1878), D iva len t (1581). Com plexes (1583), Tr iva len
t
(1108) r Titra vftlsn t (1611). Complexes (1615). H ex
av ale nt (1625).
Owbonyk (1627), Nitrosyls (1628).
Author Index . . . . . . . 1629
Ozone
861
on the earth so completely tha t stellar spectra canno t be
observed bey ond
this po int. If the ozone were sudde nly w ithdra w n, we should
all be killed
within a few minutes by the sun's ultra-violet light. H . N .
Russell
67
says
5
(i.e. at the wave-length of maximum
absorption) is as opaque as one of metal of the same mass per c .c
, so t h a t
the 3 mm . layer in the upper atmosph ere is as opaque to light of
this wave
length as three sheets of gold leaf (thickness each
1/10,000 mm .).
The absorption spectrum of ozone shows that it is not a linear
molecule
and so it must either be a ring
\Q /
The spectra indicate
that the angle is 122° and the O—O distance
1-29 A; electron diffraction gives
69
12 7+ 3° an d 1-26 A (theory 0 — 0 1-32,
O = O 1-10). This sup ports t he second formula, which
is like th a t of sulph ur
dioxide
between the two forms \ x and \ Q .
This agrees with the intense absorption band, which is found
generally in
molecules whose resonan ce forms differ in the p osition of an
electric charge ,
as in rosaniline, the cyanine dyes, the meriquinoid compounds
generally,
and prussian b lue. Sulph ur dioxide has a similar tho ugh less
intense ba nd
in the ultra-violet.
Th e energy relations are curious. As we ha ve seen, H
a
for ozone is
144-3 k.cals. Fo r the 0 — 0 we m ay tak e the normal value
of 34*9 k.ca ls. ;
for the O = O , since ozone is param agne tic, we m ust use th e
value for
molecular oxygen (118-2); but this would give 34-9+118-2 =
153-1, and
hence a negative resonance energ y; even if we assume the 0 — 0
value t o
be less (on the analogy of nitrogen) because the central oxygen has
only
one unshared electron pair, and use the value
( - 0 = 0 ) = ( 0 - 0 ) x < = g | = > = 34-9 X g g -
106-1,
we get for th e theo ry 34-9+1 06-1 = 141-0 k.cals., which gives a
resonance
energy of only 3-3 k.cals.
Ozone decomposes to oxygen very slowly at the ordinary
temperature,
but fairly quickly at 100°, and immediately at 300° (for details of
this see
Hinshelwood).
70
analysts, such as manganese dioxide, lead dioxide, and many
metals,
wipecially silver.
«
?
•• W. S. Benedict,
" W. Shand and R. A. Spurr, J.A.O.S. 1943, 65 ,
179.
10
ed. 3, 1933, pp . 80, 210.
'«« G, R. Hill,
n
L. I. Kauhtanov, N*. P . Ivanova , and V. P.
Rishov, J, Appl Ch m< Russ. 1930,
% 2170* B.CU. 1937,i.816.
Group VI. Ozone
monly acts by reduction t o diatomic o xyg en; it will convert lead
sulphide
into sulphate, lead hydroxide Pb(OH)
2
into th e dioxide, potassium iodide
in Holution int o iodine and potassiu m h ydro xide, etc. In con
tact with i t
ml vor becomes covered with a brow n layer of ox ide ; mercu ry
gives a highly
characteristic reaction, a mere trace of ozone making it lose its
mobility
and adhere in a thin film to the containing vessel.
Organic compounds are readily oxidized by ozone; even
hydrocarbons,
\ ' \
of which the —C—H group is converted into —O—OH and the / C H
into J)C=O.
72
I t will oxidize thio ether s to sulphoxides and sulph
ones.
78
ItM ox idatio n of formic acid has been show n
74
inhibited by chloride ion and by acetic acid.
A remarkable pro perty of ozone is its addition to the double
carbon link
In unsaturated compounds (C. D. Harries, 1905).
75
This can be used to
determine the position of the double link, as the ozonides
hydrolyse with
ru ptu re of th e carbon chain at this place. The addition usually
takes place
In indifferent solvents like chloroform, and the products, which
were
written by Harries as
are mostly green or colourless amorphous solids or oils, which are
often
explosive; they liberate iodine from potassium iodide, and react
with
water to give ketones (see also ref.
7 6
2
O
2
Harries's formula with the otherwise almost unknown 3-oxygen chain
is
improbable, and Staudinger suggested another,
0—ON
;
this is equally compatible with the hydrolysis to two molecules of
ketone
+ H
8
O
2
77
entirely supports Staudinger's view.
Refractivity measurements indicate the presence of only one 0—O
link;
the absorption spectra show a strong qualitative resemblance to
those of
th e peroxides. I t appea rs th at th e first step in th e
hydrolysis of these
ozonides is the splitting of the ether link; thus Harries's
'formaldehyde
peroxide' is shown to be HO - C H
2
*• J. B . Durland and H. Adkins, J.A.C.S. 1939, 61,
429.
™ H. B6hme and H. Fiacher,
Ber,
J.A.0.8. 1041, 63, 8540.
1042, 553, 187.
2
H
4
O
3
I t is an oil,
boiling under 16 mm . at 20°, and becoming a glass at
—80°; it is stable at
0°, but decomposes at the ordinary temperature (often with
explosion) to
formaldehyde and formic acid:
80
that most ozonides are mixtures of high polymers.
The heats of formation of the ozonides in the solid state or in
solution
are about 100 k.cals.
; their dipole moments are not more than 0-4 D
greater than those of the unsaturated compounds from which they
are
derived.
82
Their R am an spe ctra c ontain lines, some of which
resemble
those of the carboxylic anhydrides, and others those of the
peroxides.
88
4
This has been said to exist, and has been called oxozone
84
85
ozonized oxygen by a variety of
methods, and allowed the liquefied product to evaporate; but the
tail
fraction never gave a ny sign of th e presence of any p olymer
other th an O .
A t th e same tim e th e beh aviour of diatom ic oxygen indicates
the presence
of O
4
molecules of a kind. These were discovered b y G. N .
Lewis
86
from
87
8
(especially un der 1,000 atm .). B ut th e spectra show th a t the
two O
2
groups cannot be linked by ordinary bonds; their heat of linkage is
only
0-13 k.cal., and must be due to a kind of van der Waals force,
which will
be stronger than usual owing to the unpaired electron spins in the
O
2
molecules
89
oxygen.
is the typical associated liquid, as the following values
show:
B .
pt .
a =
90
™ E. Br ine r and P . Schnorf, ib. 1929, 12,
154.
80
Hl
»
a
E. Br iner , D. Frank , and E . Per ro t te t , ib . 1312
.
Na
E. Br iner , S . de Nemi tz , and E . Per ro t te t , ib .
762 .
u
C. D . Ha r r ies , Ber. 1912, 4 5 , 936.
m
E. Br ine r and H . B i ede rmann , HeIv. Chim.
Acta, 1933, 16, 207.
M
J.A.C.S. 1924, 46 , 2027.
" W . Fm keln burg and W . S te iner, Z. Phye. 1932, 7
9 , 69.
" O , B .
18
102
5
show the po sitions of th e oxygen a tom s, bu t no t of
course those
of the hydrogens. Ev ery oxygen atom is surrounded tetrahedrally
by
four othe r oxygens, all of them 2»76 A.U. aw ay. Since each of
these links
involves two oxygen atoms, if each oxygen has four of them, the
number
of links will be twice the number of oxygens, or equal to the
number of
hydrogen atom s, so th a t there is one hydrogen for each link. Ea
ch m ay
therefore be called a hydrogen bond, and the length is about normal
for
such a bond (0—H • - 0 in NaH CO
3
2-5-2-6 A). B ut th ey are
much longer than we should expect if the relation of the H to each
0 is
the same as in hydro xyl; in water 0— H is 0 9 5 A, so th at 0— H —
0
should be 1-90 A, whereas it is 2-76 A, 45 per cent, grea ter. This
m ay mean
either that the hydrogen is 1-38 A from each oxygen, or that it is
as usual
about
1
A from one, an d is 1-76 from th e othe r. Pa ulin g
106
concludes that
the second (unsymmetrical) alternative is true; the change in the
vibra
tion frequency of the hydrogen is too small for so large an
increase,
107
and also the symmetrical structure is incompatible with the entropy
of
ice
108
(for a further discussion of the hydrogen bond see
T. 23-32). This unsymm etrical structu re seems to mean tha t the
bond
is due rather to electrostatic attraction than to resonance.
The structure of liquid water has been discussed in a remarkable
paper
by Bernal and Fowler,
the first real attempt to discuss the physics of a
liquid. Th ey assume th a t the liquid has a sort of
pseudo-crystalline struc
ture,
with three different crystalline states in proportions
depending on
the te m pe ratu re; this is needed to explain the expansion of
water below 4°.
See further, Eu cke n
110a
.
Two molecular species derived from water are free OH radicals,
and
oxonium cations.
Free hydroxyl radicals. At high temperatures, water vapour
dissociates
with the production of hydroxyl radicals, whose absorption spectra
can be
observed at 1,60O
111
and even in the light of a carbon arc burning in
ordinary moist air.
An electric discharge in w ater vapou r produces the
same effect. Th e hyd roxy l radicals (as me asured by the
absorption spec
trum ) do not v anish as soon as th e discharge stops, bu t persist
for nearly a
second.
114
107
P . C. Cross, J . B urnh am , and P . A. Leighton ,
J.A.G.S. 1937, 5 9 , 1134.
108
W. F. Gaiuque and M. Ashley , Phys. Rev. 1933, 4
3 , 81 ; W . F . Giauque a nd
J , W. Btout , J.A.O.S. 1936, 5 8 , 1144.
1 09
E. A. Long and J . D. Kemp, ib . , 1829.
»*• J . D. Bemal and R. H. Fowler , J. Ohem. Phys.
1933, 1, 515.
nm
11 1
K. F. Bonhoaffar and H. Reiohcurdt, Z. physihal
Ohem, 1028, 139, 75.
l i l
Oxonium compounds. These are of the type
H \
+
Wld correspond in structure to the ammonium salts, though they are
less
•tab le, Th e first clearly recognized examp le of
c
3
0 • HC l discovered by Friede l in
1875: this boils at —1°, while of its components methyl ether
boils at
—28'O
0
and hydrogen chloride at —85°; it is partially bu
t no t wholly dis-
•oolated in th e gaseous st at e. In 1899 Collie an d Tickle showed
t h a t
diraothyl pyrone
a
\n/
H
formed salts like a m onacid base w ith a series of acid s: more th
an forty of
these salts are now know n. Fu rth er developments were mad e by
Baeyer
And Villiger in 1901 and the following years.
I
1
3
O]
116
has confirmed this conclusion, which is
very remarkable. An oxonium compound m ust be ionized; the structu
re
E
H
il impossible as it makes the oxygen exceed the octet limit, and a
hydrog en
bond O —H - -Cl would be too weak to hold th e part s togeth er. B
ut an
Ionized compound could not volatilize at 0°; the external electric
field of
the ions must therefore be weakened in some way, perhaps by
resonance
between (CH ) 0 H - C l a n d (C H ) 0—H [Cl].
2, A second qu estion is wh y th e pyro ne com poun ds of
Collie an d T ickle
are so read y to form oxonium salts. They ha ve tw o oxygen atom s,
and
the presence of both is necessary to produce the unusual stability
of the
salts, so they mu st b oth tak e p art in the structure. This is
explained by
114
J.
110
TfWM
1
(J.C.S. AUtr, 1923,11. 500).
Oxonium Compounds 867
the p roduction of an arom atic structu re (with its various
resonance forms)
O 0—H
H(X XM H
3. Three of the four forms of the oxonium ion
(1) [H
+
(R = hy droc arbo n radical) ha ve long been kno wn , being formed
w hen an acid
like hydrog en chloride is dissolved in wate r, alcohol, and ethe r
resp ectively.
The fourth type, [R
, in which all three hydrogen atoms are replaced,
has recently been discovered, and many of its salts isolated by
Meerwein
and his colleagues.
11 8
They showed th t if the com pound of boron tri-
fluoride with ether Et
epiohlorhyd™
C l
a semi-solid m ass is formed, of which th e solid pa rt is th e
trieth yl oxonium
salt Et
4
]. I t is very uns table, and m elts at 92° with
decomposition
to Et
3
an d eth yl fluoride, from which also it can b e made b y he
at
ing them in a sealed tu be . W ith sodium picrate this salt gives
the picrate
Et
3
6
H
2
(NOg)
3
O], m. pt . 58° with decomposition; attem pts to m ake the
iodide w ith potassiu m iodide failed. Th e borofluoride is a very
powerful
ethylating agent: with water i t gives ethyl ether+alcohol, with
phenol
phe neto l, etc. Ep ichlorh ydrin will also act
119
etherates of antimony pentachloride, aluminium chloride, and
ferric
chloride, giving th e salts (if R = E t
3
4
O Their salt chara cter is prove d by their solubility in nitro
-
methane and in sulphur dioxide, and their high conductivity in the
latter
solvent.
poses, but by measuring the conductivity at intervals, and
extrapolating
back to zero time, it can be shown that Et
3
high order of streng th as Me
4
3
4 2 6
4
2
0-X+R-ha l ; t hey a re r emarkab ly
powerful alkylating agents.
118
H. Meerwein, G. Hinz, P. Hofmann, E. Kroning, and E.
Pfeil, J. prakt.
Oh$m.
119
1
prakt.
OUm.
\m
Group VI. Oxygen, Hydrides
H Y D R O G E N P E R O X I D E
Tms is the primary product of the action of oxygen on hydrogen: it
is
formed in small qu an tity w hen hydrogen bu rns in air/
1905
or when a m ixture
of hydro gen and oxygen is passed over palladiu m b lack. I t is
comm only
made by the action of acids on sodium or barium peroxide, or
recently
often through peroxy-disulphuric acid by the electrolysis of acid
sulphates
in concentrated solution in presence of hydrofluoric acid or
potassium
ferroeyanide; it is concentrated by fractional distillation under
reduced
pressure.
2
O
2
is an o ily liquid , freezing a t —1*7° b u t v ery easily
supercoo l
in g ;
b . p t. 69-7°/28 m m ., ext rap ola ted 144°/760 m m .
I t h as all the proper
ties of a highly associated liquid, and physically resembles w ater
ver y
closely. I t ha s an even higher dielectric co ns tan t of 89-2 a t
0° (wa ter
84-4/0°): a m ixtu re of the tw o has a still higher dielectric con
stant , 120 in
a 80 per cent, solution.
120
I t is miscible with w ater in all propo rtions, bu t
relatively slightly soluble in non-associated liquids.
1211
I t is an excellent
ionizing solvent, in which salts are about as much dissociated as
in water,
though weak acids like acetic are very much less so.
The specific conductivity of pure H
2
O
2
6
120
which
implies a con centratio n of hyd rogen ion 50 time s as grea t as
in pure w ater,
and a dissociation co nsta nt of ab ou t 10 ~
12
about
10"
16
.
This result is confirmed b y the potentiom etric titra tio n
w ith
potassium hydroxide, which gives l-55xl0~
1 2
at 20°.
122
Hydrogen
peroxide is th u s definitely more acidic th an w ater (compare
carbonic acid,
k
).
It is endothermic and very unstable, readily breaking up according
to
the reaction
2
O
2
(b.p t. 144°) has th e same Tfouton constan t as w
ater
(a difference of 1 in this co nstant would only mak e a
change of 0*84 k.cals.)
the heat evolved if all the substances were gaseous would be 49*3
k.cals.
The reaction really consists in the replacement of 2 O—0 links by
the
double link in molecular oxygen, and so should evolve
118-2 - 2 x 34-9 = 48-4 k.cals .;
so the resonance energy seems to be much t he same in hy drogen
peroxide
as in wate r. Fo r this qu estion, and th e heat of th e O—O link,
see further,
references
123
.
In the complete absence of catalysts hydrogen peroxide remains for
a
1 1 Q a
See A. C. G. Egerton and G. J. Minkoff, Proc. Roy.
Soc.
1947, 191, 145.
J.A.C.S.
18 1
J. H. Walton and H. A. Lewis, ib. 1916, 38, 633.
"» V. A. Kargin, Z, cmorg. Q U m , 1029, 183
, 77.
188
m
G. Glooklor and G, Matl&ok, JT, Ohm.
Phy*. 10 46,14 , 804,
m
Q
9
Hydrogen Peroxide 869
long time unchanged, but its decomposition is promoted by a very
large
number of substances, such as alkalies, potassium iodide, finely
divided
platinum and palladium, and certain enzymes known as
catalases.
All finely divided and sharp-edged solids, even dust, promote the
decom
position, and so the concentrated substances is commonly kept and
sold
in paraffin vessels. On th e other ha nd , certain sub stances,
even in small
quantity, such as phosphoric and uric acids, are very effective in
delaying
th e decomposition. 1 g. of uric acid will stabilize 30 litres of
concen
t ra ted H
126
Hy drogen peroxide can act bo th as an oxidizing and as a reducing
agen t.
It s power of oxidation is most ma rked in alkaline solution: it
can convert
ferrous salts into ferric, sulphurous into sulphuric acid, hydrogen
iodide
into iodine, etc . It s reducing power is due to its remo ving
oxygen atom s
from othe r molecules in th e form of diatom ic oxygen . Th us
silver oxide is
reduced to silver, and potassium permanganate to a manganous salt;
this
reduction may often be due to the formation of an intermediate
unstable
oxidation product with an — O—O— group
H
2
O
2
O + A— 0—0;
w ith chromic acid a blue perchromic 'a c id ' is prod uced , which
easily loses
oxygen to give a chromic salt. (For the kinetics of th e hom
ogeneous
decomposition of H
iodine, etc., see references
thallium, and lead amalgams see reference
m
. )
Hydrogen peroxide shares with water the power of acting as a
donor,
and can replace water of crystallization in man y salts.
There are two possible structures for H
2
O
2
H \
W
By treatment in alkaline solution with dialkyl sulphate it can be
con
verted into its dialkyl ethers, such as (CH
3
J
2
O
2
2
Hg)
2
O
2
,
b, pt. 65° (both at 760 m m .). These compo unds on
reduc tion give alcohols,
A l k \
so tha t they have the s t ructure AIk—0—0— AIk, and not y 0 - >
0 ,
which on redu ction would give an ethe r. This does no t, however,
settle the
structure of the hydrogen compound, which may well be tautomeric;
the
126
Fo r an accou nt of the physical and chemical properties
of 90 per cent, aqueous
hydrogen peroxide, see E. S. Shanley and F. P. Greenspan,
Ind. Eng. Chern.
187
N . I. Kobozev and E . E. Galbreioh, J . Phy$.~Chem.
Buss, 1940, 14, 1550.
188
m
1
258.
m
From hydrogen peroxide are derived a large number of
compounds
containing the O—O link: not only organic derivatives such as the
alkyl
and acyl peroxides, the percarboxylic acids like
C
6
H
5
\Q—0—H
bu t also many inorganic derivatives, in which one or more oxygen
atom s of
a basic or acidic oxide, or an oxy-acid, are replaced by O—O grou
ps. The
bina ry inorganic compounds are comm only known as peroxides: this
nam e
should be confined to O—O compounds, but is often extended to
include
any metallic oxides with an unusually large amount of oxygen, such
as
PbO
2
and
MnO
2
.
These tw o classes are as a rule easily distinguished. Th
e
oxide will dissolve in acids, and then if it contains a true O—O
link, the
solution will contain H
). If it is not a true peroxide,
bu t an ox ide of an un stable high valen cy, this will often be
reduced b y t he
acid (as Mn0
hydrogen peroxide.
True peroxides are those of the alkalies and alkaline earths, which
are
undoubtedly salts (Na
hydroxides M'[0
13 7
analysis which gives the O • • O distan ce in SrO
2
1-32).
M etals wh ich are less electro-positive, or in other w
ords
go over more readily into the covalent state, such as zinc,
mercury, and
nickel, give less certain or at any rate less stable
peroxides.
Other compounds with the O—O link are numerous per-acids (or
peroxy-acids), such as persulphuric, perboric, percarbonic,
pertitanic,
perchrom ic, etc . Th e elemen ts of th e A subgrou ps of Groups IV
, V, and
VI form these very readily, and they are most stable in the even
groups,
and in each group with the heaviest element.
139
1-34 A.
A doubt whether some of these compounds are hydrated peracids,
or
normal acids with hydrogen peroxide of crystallization can often
be
settled by the 'Riesenfeld-Liebhafsky test ' .
1 4 1
H
7*5-8*0 tru e peroxides, such as po tas
sium persulphate K
peroxide
itself,
2
O
2
of crystalliza
tion, give no iodine b u t liberate oxy gen. W hen this test is
positive—when
it gives I
2
- i t is good evidence of a true O—O link not attached to
two
"
188
J. D. Bernal, E. Djatlova, I. Karsanovski, S. Reichstein,
and A. G. Ward,
7J. Krist.
Z. anorg. Ohem .
1899, 20, 840.
1933, 223, 887.
compound
has
in the
solution, either
because it was there as hydrogen
peroxide of crystallization, or
because
the X—O—O—H group was so unstable as to
react with the water to
form X—O—H and H
2
O
2
.
By this test it can be shown th at we hav e tr
ue peroxides (i.e. molecules
with
an
2
CO
4
R
8
]. But the supposed per-compounds of
silicon, germanium,
and thorium seem to be only normal oxides with hydrogen
peroxide of
orystallization.
Organic Peroxides
Almost all classes of organic oxygen
compounds can have an oxygen
atom replaced
are the
alkyl hydro
peroxides or per-alcohols AIk—O—O—H and the
dialkyl peroxides
AIk—O—O—AIk; these were first made by Baeyer
and Villiger
14 2
Boiling-points [and Melting-points]
[-13-5°]
a =
u
\ b =
145
tively. The per-alcohols decompose readily when
concentrated, and are
difficult to purify. The dialkyl
peroxides are relatively
stable, but explode
on heating above their boiling-points.
I n chemical beha viou r (our knowledge is mainly of th e ethy l
com pounds)
the per-alcohols
14 8
are in most points, but not in all, intermed
iate between
the alkyl peroxides and hydrogen peroxide. They are
far less stable th an
the peroxides, which are almost
as inactive as ether ; the alkyl
groups in
AIk—0—0—AIk are not oxidized by
permanganate or by chromic acid,
and the 0—0 link is not reduced by
sodium alone, and only very slowly
by potassium iodide in presence of strong
sulphuric acid; it is, however,
142
Ber.
144
148
P, Giorgt and A. D,
Wabh, Tram. Jar, Soo. 1940, 42, 94.
i" N.
A. MIlM
and D.
873
reduced quantitatively by zinc and acetic acid with the production
of
ethyl alcohol, a proof that the structure is Et—O—O—Et and
not
E t \
) 0 - > 0 .
E t /
But the vapour catches fire in air in contact with a thermometer at
250°
(carbon disulphide does not do so below 300°), and if the liquid,
in an
atmosphere of carbon dioxide, is touched with a hot wire it
vanishes, the
m ain pro du ct being formaldehy de. Th e dialkyl peroxides hav e a
faint
smell like th a t of eth yl brom ide, while eth yl per-alcohol
smells like b leach
ing powder and acetaldehyde.
H is a weak acid about as strong as phenol,
forming salts with alkalies and alkaline earths which are explosive
and
are decomposed by carbon dioxide. I t differs m arkedly from hyd
rogen
peroxide, having practically no reducing power, but only
oxidizing.
Chromic, molybdic, and titanic acids (which might either be
reduced,
e.g. to chromic salts, or oxidized to per-acids) have no action on
it; acid
permanganate is much more slowly decolorized by it (with evolution
of
oxygen) th an by hydrog en peroxid e. Silver oxide (which at once
reduces
hydrogen peroxide) has scarcely any action on the per-alcohol,
while
ordinary molecular silver, which has no action on hydrogen
peroxide,
decomposes th e per-alcohol, sometimes explosively. On the other ha
nd, it
is a strong oxidizing agent; it oxidizes hydrogen iodide, with
explosion in
concentrated solution, and it can convert tertiary amines into
amine
oxides.
is abnormally stable; unlike the
other esters it can be made from the alcohol and hydrogen peroxide
with
a dehydrating agent (MgSO
); it will stand for months in the
cold w ith 10 per cent, sodium hydrox ide solution witho ut chang
e. Fo r th e
kinetics of its decomposition in the gas at about 150° see
reference
148a
149
that in the oxidation of
petrol by air, and in the 'knocking' of petrol engines under
excessive
compression, the alkyl peroxides and per-alcohols are probably
starters of
reaction chains. They find th at diethyl peroxide is a strong
'pro-k no ck',
and also th at it gre atly shortens th e induction period of the
slow ox idation
of propane.
N um erous organic peroxides of other typ es are known, such as the
per-
anhydrides. Peracetic anhyd ride CH
3
was made by
Brodie in 1863 from acetic anhydride and barium peroxide; it melts
at
30°, boils a t 63°/21 m m ., and is enorm ously explosive.
Benzoyl peroxide
®«CO"O
2
'CO*<I> is used in organic chemistry as an oxidizing agent;
for
14Sa
J. H. Haley, F . F. Bust, and W. E. Vaughan, ib.
1948, 70, 88.
u o
"° Id., Proo. Boy. Soo. 1038, 168, L
151
E. J . H arris lb. 1989» 173, 126; 175, 254.
169
1 . 0. Stathii and A, 0, E gar
ton, Trans. Far. 6
1
Qd.
the kinetics of its decomposition, see references
153
thermal decomposition see references
H can be made by the hydrolysis of these per-
anhy drides, or by th e action of hydrogen peroxide on th e ord
inary acids in
presence of sulphuric acid
H melts at +0*1°
and explodes at 110°, which is tak en to b e its
boiling-point.
15 8
P . H . H e r m a n s , Bee. Trav. 1935, 54 ,
760.
15 4
HeIv. CHm. Acta,
1936, 19 , 338 .
16 6
J . D . B r o w n , J.A.G.S. 1940, 6 2 , 2657
.
15 6
Ber.
um
P . D . Ba r t l e t t and K . Nozak i ,
J.A.G.S.
1686
di-mercaptan C
197
The
mercaptans, like the phenols, dissolve in alkalies to form salts,
which are
considerably b ut by no m eans completely hy drolysed.
The polymethylene dimercaptans HS(CH
2
(SH)
2
could not be made. Their melting-points show
a sharp alternation, those with n even being 20-40°
higher than the next
with n odd. The dibromides and glycols behave in the sam
e way.
Though the alkaline derivatives of the mercaptans are no doubt
true
salts, those of the heavy metals are certainly as a rule
covalent, especially
those of mercury (see II. 320) and divalent lead; the latter, like
the
mercury compounds, have very low melting-points, for example,
(Et-S)
2
199
and are soluble in chloroform and benzene; these are almost the
only
covalent derivatives of divalent lead.
Like hydrogen sulphide the mercaptans are very easily oxidized;
thus
sulphuric acid, instead of forming alkyl thiosulphates AIkHS
2
O
8
as
AIkHSO
4
is formed from alcohol, oxidizes them to the
di-sulphides.
Stronger oxidizing agents con vert the m into sulphonic acids A
Ik-SO
3
H .
Thioethers
These resemble the O-ethers fairly closely in physical properties;
they
are immiscible with w ater, the y are said to have no smell when
pure, and
they boil about 60° higher than their oxygen analogues; examples
are:
M e
3
209
The barrier to rotation of the methyl group is found from the
specific
heat of the vapour to be 1-5 k.cals. in CH
3
-SH
1 0 8
W. P . Ha l l and E . E . Re id , J.A.G.S. 1943,
6 5 , 1466.
1 0 9
E . We r the im , ib . 1929, 5 1 , 3661.
2 0 0
(J.G.S. Ahstr.
J.A.G.S.
Theory of Resonance,
1944, p . 70.
una j p
m
ore of these see JRichter, ed. 12, i i . 3, p. 21.
804
F . S . Fawce t t and H . E . Rasmussen ,
J.A.G.S. 1945, 6 7 , 1705.
908
1 0 1
goi H
§
^ r , T h o m p s o n a n d J . W . L i n n e t t ,
Tram. Far. Soo. 1985, 31, 1743.
m
C—S—C
tho diaryl sulphides, where the aryl groups might be expected to
increase
It * it is little if at all larger than the tetrahedral
angle (in H
2
/ S w v
has a moment of 1*50 D in carbon tetrachloride, so it must be
non-planar
with the S-angles less than 120°
210
; the dipole moments of their para-
subs titution compounds show th a t th e valency angle in diphenyl
sulphide
m I13±3° ,
2 1 2
2 1 1
6
H
4
2
S
gives the C—S—C angle as 112*4+1-5° and the 0—S
distance as 1-71
(theory 1-81).
C H - CH
Thiophene CH CH
odours up to 0-5 per cent, in crude benzene, and causes it to give
th e ind o-
phcrnin reaction (a blue-green colour with a trace of isatin in
concentrated
sulphuric acid); it can be made by heating succinic acid with
phosphorus
pentasulphide, or
by passing acetylene over pyrites at 300°.
I t is a colourless liquid smelling like benzene, to which it has a
rem ark ably
close resem blance. Ele ctro n diffraction
201
shows the molecule to be p lan ar,
w ith th e distances C - C 1-44, C = C 1-35, C - S 1-78 (theory C -
C 1-54,
CU=C i'3 3 , C—S 1*81, C = S 1-61 A). Th e resonance energy as m
easured
by t he he at of com bustion is 29 k.cals.
202
(benzene 41). In physical prop er
ties, a nd especially in boiling-points, thiophe ne and its
derivatives closely
resemble their benzene analogues, as the following values
203
204
205
[110-8°];
aoetyl-thiophene
206
213-9° [202°]; dith ienyl 266° [254°]. I ts chemical
resemblances are equally close; it is as readily chlorinated as
benzene,
more easily sulphonated, an d rathe r less easily nitra ted. I t
can be removed
from benzene through its more rapid reaction with sulphuric acid
(V.
Meyer) or w ith mercuric ace tate (Dim roth). I t reacts like
benzene with
diazoacetic e ster.
203
E ve n the physiological action of drugs like cocain a
nd
atropine is little affected if their phenyl groups are replaced by
thienyl.
203
The sulphur in a thioether h as a marked action on the behaviour of
other
atom s in the molecule. F or exam ple, the a cidity of a phenol is
enormously
increased by the attachment of a sulphur atom to the benzene ring,
as in
910
111
L. 1. Button and O. 0. Hampion, Trmt. Wm.
Soo,
1985, 31, 045,
L. 1. Button and O. 0. Hampion, Trmt. Wm.
Soo,
1985, 31, 045,
1OiQ
1
73,107.
An other effect w hich has become only too well
know n is on a chlorine atom atta ch ed to carbon . If one of th e
a-hydrogen
atoms in diethyl sulphide is replaced by chlorine, as in the
dichloride
(GH
3
—CHCl—)
2
S, no special peculiarities are observed except that the
chlorine is very easily replaced. B ut if the chlorine atom s are
in th e j8-
position, as in (CH
S, two effects are produced; firstly, the
chlorine atom becomes much more difficult to remove, and secondly,
the
substance acquires an intense physiological activity, especially
the power
of raising blisters in con tact w ith th e skin. I t is of course
th e well-known
m ustard gas. The a-compound has no vesicating power. This
distinction
runs through all the chloro-thioethers, and the two properties
always go
together.
The thioethers, like the ethers, form a series of addition
compounds,
often with the same substances, the sulphur being on the whole
perhaps
as good a donor as the oxygen, though it is somewhat limited in its
action.
Comparison is difficult, because the additive powers of the sulphur
com
pounds are for obvious reasons much less thoroughly investigated
than
those of their oxygen analogues. B ut so far as we know the m
ercaptans
form very few addition compounds, only some three being
described:
SbCl
3
4
, 1 and 2 Et S H (the last two both red), so th at they
are very different from those of the alcohols. Presumably the same
condi
tions which cause the hydrogen to ionize weaken the donor power of
the
sulphur.
The addition compounds of the th ioethers are num erous. They
include
a rem arkable group in which th e acceptor atom is carbon. Ingold
an d
214
treated with potassium hydroxide loses hydrogen bromide to give
a
neutral product which is monomeric in benzene and must have
the
structure (II):
[ C
6
(I) (H)
This pro du ct is dim ethyl-sulphon ium -9-fluorenyhdide ; it is
one of th e rare
cases wh ere a carbon atom forms a co-ordinate link. Th e altern
ative
structure with a double link
/ \CH
3
is impossible for various reason s, the simp lest of which is th a
t th e comp ound
reacts with dilute hydrobromic acid like a base, taking up the acid
and
regenerating a sulphoirium salt (corresponding to I), the carbon
atom,
with t he valency group 2, 6 behaving like the n itrogen atom of an
am ine,
while the tr ue C S group (as in carbon disulphide) does no t do t
h is ;
918
1985, 200» 762,
1
718.
S84 Group VI. Sulphur, Organic Compounds
a n o t h e r r e a s o n i s t h a t t h e > C = S < s t r u
c t u r e w o u l d i m p l y a v a l e n c y
group of 2 , 8 ( iner t pa i r ) for the sulphur a tom.
In ano the r smal l g roup o f co -o rd ina t ion compounds o f the
th ioe the rs i t
i i n i t rogen th a t ac t s a s accep to r . These a re th
e sulphylimines, which a re
of th e ty pe Q
t /x
2 15
by the ac t ion o f ' ch lo ramine-T ' ( the sod ium sa l t
o f the su lphon-
oh lo r ide ) on a th io e the r . The i r whole beha v iou r suppo
r t s th e — ISk-S as
a g a i n s t t h e — N = S s t r u c t u r e . T h e y h a v e b e
e n r e so l v ed i n t o s t a b l e
a r i t imers .
2 1 6 - 1 7
Apar t f rom these , the add i t ion compounds o f the th ioe the r
s a re a lmos t
confined to a sm al l gro up of e lem ents in th e per iodic tab le
,
2 1 8
wh ich on th e
whole a re those tha t fo rm the mos t s t ab le meta l l i c su
lph ides .
2 1 9
These
compounds are formed by the hal ides (and wi th s i lver by the n i
t ra te) of
the fo l lowing e lements :
N i Cu Zn
P d Ag Cd
P t Au Hg
an d otherw ise only by those of Al , Ti , an d Sn, th e s tan nic
hal id es , as usua l ,
t ak ing u p tw o molecu les o f th e su lph ide ; the d i su lph
ides AIk
2
S
2
can re plac e
th e th ioe the r s . Th us we hav e th e fol lowing de r iva t
ives of d im eth y l
t h io e t he r C H
3
2
S .
SnCl
4
2
S .
Tsohugaeff
220
showed th a t d i th ioe the rs of th e ty pe R - S -
(CH
2
form such compounds unusua l ly eas i ly when
n
8-ring can be formed as in : - ^
C l \
918
*
w
S. G. Clarke, J. Kenyon, and H. Phillips, ib. 1927,
188.
817
For further work on these compounds see L. A, Pink and
G.
•» See G. T. Morgan and W, Ledbury,
J.CS.
•» See G. T. Morgan and W, Ledbury,
J.CS.
«• L, A. Ttohug&eff, B$r, 1901, 41 , SSlS.
N a
4
S
5
, is ru n in to cooled hydrochloric a cid, a yellow oil
separates , which is
mainly a solution of sulph ur in a mix ture of th e only isolated
polysulphides
of hydro gen, H S
2
H
2
B and sulphur so readily, especially in presence of traces of
alkali, that
the calcium chloride used to dry them, and the apparatus in which
they
iiro distilled, mus t be previously tre at ed w ith gaseous
hydro gen ch loride.
225-7
The two sulphides are then isolated by fractional distillation at
low
pressures.
pressure at 71°.
2
, benzene, and eth er: it is rapidly decomposed by
water, alcohol, alkalies, and sulphuric acid, but can be dried with
P
2
O
6
.
It dissolves sulphur, bu t is no t thereby converted into the
trisulphide. I t
gives a normal molecular weight by the freezing-point in
bromoform.
228
N s — s / or N s S
v
Na
witli the S—S distance 2'05±0'02 A (theory 2-08); this agrees with
the
Haitian spectrum,
2
O
2
231