Herbert E Williams.

The chemistry of cyanogen compounds and their manufacture and estimation online

. (page 1 of 35)
Online LibraryHerbert E WilliamsThe chemistry of cyanogen compounds and their manufacture and estimation → online text (page 1 of 35)
Font size
QR-code for this ebook


THE CHEMISTRY OF
CYANOGEN COMPOUNDS

AND THEIR MANUFACTURE
AND ESTIMATION



BY



HERBERT E. WILLIAMS




LONDON
J. & A. CHURCHILL

7 GREAT MARLBOROUGH STREET
1915






<



TO

c. w.



,V!14U



PREFACE

SOME years ago the author was interested in the
production of cyanogen compounds, but found no
up-to-date work on the subject : the information with
regard to these bodies in the existing chemical dic-
tionaries was unsatisfactory and often incorrect and
misleading.

There were several excellent books dealing with
the production and application of cyanides, but
such chemistry as these books contained was mainly
copied from the existing dictionaries and was charac-
terised by the same inaccuracy and unsatisfactory
nature.

The chemistry of these compounds had, however,
not been left unregarded, as some considerable amount
of original research and information has been published
in the numerous technical and scientific journals, most
of which is swamped by the great tide of organic
chemistry of the last quarter of a century.

An attempt has been made by the author covering
a number of busy years, to check the composition and
properties of the cyanogen compounds, particularly
the metallic salts, but although many hundreds of
these compounds have been prepared and examined,
the task has so far proved too great to complete, and
the major portion yet remains to be accomplished.

In this little book an effort has been made to rescue
iii



327626



iv PREFACE

the information scattered through the scientific press
a task of no mean magnitude, as the index of many of
the journals was of little if any use to check the
composition and properties of the compounds described
as far as possible ; and to add a small quota to our
knowledge of these compounds by such reactions as
were brought to light in the course of the author's
work. An attempt was made to publish some of the
information so obtained through the scientific societies,
but it was found that the time required to comply with
the petty restrictions and to conform to the stereo-
typed methods usually quite irrelevant to the subject-
matter was so great that it was much better employed
in further investigation.

The book has been arranged to give an outline of
the compositions and properties of the various cyanogen
compounds ; and to describe briefly the manufacture,
application and estimation of such compounds as are
met with in commerce.

Great care has been taken to record the various
sources from which the information has been taken,
and it is hoped that all such sources are duly acknow-
ledged.



CONTENTS

PART I
CHEMISTRY OF CYANOGEN COMPOUNDS

CH AP. PAGE

I. Cyanogen and the Cyanogen Haloids i

II. Cyanamide and Allied Compounds 16

III. Simple Cyanides 32

IV. Iron Cyanogen Compounds : The Ferrocyanides 84
V. Iron Cyanogen Compounds : Ferricyanides,

Carbonylferrocyanides, Nitroferricyanides, Per-
ferricyanides, etc. 131

VI. Oxycyanogen Compounds. Cyanic, Cyanuric,

Fulminic, and Fulminuric Acids 171

VII. Thiocyanates and Selenocyanates 188

PART II

MANUFACTURE AND APPLICATION OF CYANOGEN
COMPOUNDS

VIII. Manufacture of Ferrocyanide 217

IX. Manufacture of Ferrocyanides 227

X. Manufacture of Thiocyanates and Cyanamide 255
XI. Manufacture of Cyanides from Ferrocyanides and

Thiocyanates 268

XII. Synthetic manufacture of Cyanides 285

XIII. Manufacture of Fulminates 315



vi CONTENTS

PART III
ANALYSIS OF CYANOGEN COMPOUNDS

CHAP. PAGE

XIV. Analysis of Cyanides 3*8

XV. Analysis of Ferrocyanides 343

XVI. Analysis of other Iron Cyanogen Compounds 375

XVII. Analysis of Thiocyanates and Cyanates, &c. 388

USEFUL TABLES 405

INDEX OF NAMES 409

INDEX OF SUBJECTS 415



ABBREVIATIONS OF THE TITLES OF
JOURNALS, ETC.



Abbreviated title
A.

Am. Chem. J.
Ann. Chim. Anal.



Ann. Chim. Phys.
Ann. Set. Univ. Jassy

Arch. Pharm.

Atti R. Accad. Lined

Ber.

Boll. chim. farm.
Bull. Soc. chim.
Chem. News
Chem. World
Chem. Zeit.
Chem. Zentr.
Compt. rend.

D.P.J.
E.P.

Gazz.
J-

J. Am. Chem. Soc.
J.C.M.M.S.,S.A.

J.c.s.

J. Ind. Eng. Chem.

J. Pharm. Chim.

J. pr. Chem.

J. Russ. Phys. Chem.

Soc.
J.S.C.I.



Journals, etc.

Liebig's Annalen der Chemie
: American Chemical Journal
Annales de Chimie analytique appliquee
a 1' Industrie, a 1' Agriculture, a la Phar-
macie, et a la Biologic
= Annales de Chimie et de Physique
: Annales scientifiques de PUniversite de

Jassy

: Archiv. der Pharmazie
Atti della Reale Accademia dei Lincei
Berichte der deutschen chemischen Gesells-

chaft

Bollettino chimico farmaceutico
Bulletin de la Societe chimique de France
= Chemical News
: Chemical World
Chemiker Zeitung
Chemisches Zentralblatt
J Comptes rendus hebdomadaires des

Seances de 1'Academie des Sciences
Dingles polytechnisches Journal
English Patent
Gazzetta chimica italiana
Jahresbericht iiber die Fortschritte der

Chemie und verwandter Theile
Journal of the American Chemical Society
Journal of the Chemical Metallurgical and

Mining Society of South Africa
Journal of the Chemical Society
Journal of Industrial and Engineering

Chemistry

Journal de Pharmacie et de Chimie
Journal fur praktische Chemie
Journal of the Physical and Chemical

Society of Russia

Journal of the Society of Chemical In-
dustry
vii



viii ABBREVIATIONS

Abbreviated title Journals, etc.

J. S. Dy. 6- Col. = Journal of the Society of Dyers and

Colourists
P. = Proggendorff's Annalen der Physik und

Chemie

P.C.S. = Proceedings of the Chemical Society

Pharm. Weekblad = Pharmaceutisch Weekblad

Phil. Trans. = Philosophical Transactions of the Royal

Society of London

R.P. Repertorium fur die Pharmacie

T.C.S. = Transactions of the Chemical Society

U.S.A. Pt. = United States of America Patent

Z. anal. chem. = Zeitschrift fur analytische Chemie

Z. angew. chem. Zeitschrift fur angewandte Chemie

Z. anorg. chem. = Zeitschrift fur anorganische Chemie

Z. Kryst Min. = Zeitschrift fur Krystallographie und

Mineralogie
Z. dffentl. Chem. = Zeitschrift fur offentliche Chemie



THE CHEMISTRY OF CYANOGEN
COMPOUNDS

PART I

CHAPTER I
CYANOGEN AND THE CYANOGEN HALOIDS

As hydrocyanic acid (prussic acid) may be produced
by the fermentation of certain glucosides, which occur
naturally in a few plants, it is possible that hydrocyanic
acid was used by the ancients as a poison. The first
authentic knowledge of the compounds of cyanogen,
however, date from the discovery of prussian blue in
1704 by Diesbach ; but little was known of the
chemical properties of the compound until Maequer in
1754 prepared potassium ferrocyanide by crystallizing
the filtered solution, obtained by treating the blue
with caustic potash.

The discoveries of Scheele in 1782-83, Berthollet in
1790, and Gay Lussac in 1815, considerably advanced
the knowledge of the chemistry of prussian blue and
potassium ferrocyanide, and clearly snowed the relation
of these bodies to hydrocyanic acid and cyanogen. ;
the brilliant work of Liebig and Wohler in this field
very considerably increased our knowledge of this
interesting series of compounds, a knowledge that has
steadily increased from that time to the present day..

Although hydrocyanic acid had been prepared by
Scheele in 1782, it was not until 1815 that cyanogen

j i



2 ''THE 'CHEMISTRY OF* CYANOGEN COMPOUNDS

was isolated in a pure state by Gay Lussac. The
discovery of this gas was one of far-reaching importance
to theoretical chemistry, as it is the first recorded
instance of the isolation of a compound radicle.

Cyanogen may be fairly readily obtained by a
number of reactions, such as :

1. The action of heat on the cyanides of the noble
metals :

Hg(CN) 2 = Hg + (CN) 2 .

2. By the dry distillation of ammonium oxalate in
the presence of a dehydrating substance, such as
phosphorous pentoxide :

(NH 4 ) 2 C 2 4 + 2P 2 5 = (CN) 2 + 2H 4 P 2 7 ;
or w'th glycerine :

(NH 4 ) 2 C 2 4 = (CN) 2 + 4 H 2 0.

3. By heating dry potassium ferrocyanide with
mercuric chloride :

K 4 Fe(CN) 6 + 3 HgCl 2 = 4 KC1 + FeCl 2 + 3 Hg + 3 (CN) 2 .

4. By heating dry zinc cyanide and cupric chloride
to i6o-i70 C. :

2 Zn(CN) 2 + 2 CuCl 2 = 2Cu(CN) + (CN) 2 + 2ZnCl 2 .

5. It may also be prepared in the wet way, by
boiling a solution of cupric sulphate, or chloride, to
which is gradually added through a stoppered funnel
a strong solution of sodium, or potassium cyanide. 1
The cupric cyanide at first formed decomposes into
cuprous cyanide and cyanogen :

4 KCN + 2CuSO 4 = 2CuCN + (CN) 2 + 2K 2 SO 4 .

The cyanogen is evolved in abundance together with
water vapour ; no reaction occurs with the latter, and
the cyanogen at the temperature of the reaction, nor
is any of the evolved cyanogen converted into para-
cyanogen.

6. The gas may also be produced in a manner
similar to the preparation of chlorine ; thus when

1 Jacquemin, CompL rend. (1885), 100, 1005.



CYANOGEN AND THE CYANOGEN HALOIDS 3

sodium, or potassium cyanide solution is electrolyzed,
using an iron cathode and a carbon anode, cyanogen
gas is liberated at one pole and hydrogen at the other.
It may also be produced by distilling a cyanide with
manganese dioxide and sulphuric acid.

Dry cyanogen gas is most conveniently prepared by
the dry distillation of mercuric cyanide (Gay Lussac) ;
or any dry cyanide, or ferrocyanide mixed with the
equivalent quantity of mercuric chloride, the gas
being collected over metallic mercury. A portion of
the cyanogen, however, polymerizes to form a dark
brown substance called paracyanogen. It is necessary
that the cyanide used should be quite dry, otherwise
the water-vapour will react with the cyanogen at the
temperature of the tube to form ammonia, carbon
dioxide, and hydrocyanic acid :

(CN) 2 + 2H 2 O = HCN + NH 3 + CO 2 .

Cyanogen gas is colourless and inflammable, burning
with a peach-coloured flame ; it has a pungent odour,
but strongly suggests hydrocyanic acid ; it attacks
the eyes and nose, and is excessively poisonous.
Under a pressure of about 4 atmospheres at normal
temperature, or at normal pressure but cooled to
- 20.7 C., cyanogen gas is condensed to a transparent,
colourless, and very mobile liquid of sp. gr. 0.866 at
17 C., and on further cooling may be obtained in
crystals melting at 34.4 C. It has a critical
temperature of 128.3 C. and a critical pressure of
5 or 6 atmospheres. 1

It is decomposed into its elements by the electric
spark, and does not readily unite directly with hydro-
gen, only a trace of hydrocyanic acid being formed
by passing the two gases through a tube heated to
500 C. ; combination, however, takes place when the
mixed gases are heated to 500 C. in a sealed tube.

Water dissolves four and a half times its own
volume of the gas ; alcohol twenty-five times and

1 E. Cardoso and G. Baume, Compt. rend. (1910), 151,
141-43 ; /.C.5., i. 605 (1910).



4 THE CHEMISTRY OF CYANOGEN COMPOUNDS

ether five times. The aqueous solution rapidly be-
comes dark coloured with formation of azulmic acid,
ammonium oxalate and carbonate, hydrocyanic acid,
urea, and other products.

Metallic sodium or potassium combine directly with
cyanogen when heated in the gas, to form a cyanide
of the alkali metal.

The gas when passed into a solution of an alkali
hydroxide forms a mixture of cyanide and cyanate :

2KOH + (CN) 2 = KCN + KCNO + H 2 O.

By substituting a solution of a sulphide for the
hydroxide a mixture of cyanide and thiocyanate is
formed :

K 2 S + (CN) 2 = KCN -f KCNS,

When passed into strong aqueous hydrochloric acid,
crystals of oxamide, C 2 N 2 H 4 O 2 , are deposited after
some time, while a small quantity of ammonium
oxalate remains in solution. Strong aqueous hydri-
odic acid also yields oxamide, with liberation of
iodine ; and the solution contains hydrocyanic acid
and ammonium iodide.

By the action of nascent hydrogen, cyanogen is
converted into ethylene diamine :

(CN) 2 + 4H 2 =(C 2 H 4 )N 2 H 4 ;

and it combines directly with hydrogen sulphide to
form a mono- and di-cyanogen sulphydrate.

Glacial acetic acid absorbs about eighty times its
own volume of cyanogen, and it is also absorbed by a
3 per cent, solution of hydrogen peroxide with evolution
of oxygen ; if a little caustic potash solution is added
after a few minutes, needles of oxamide separate free
from by-products. 1

The gas also combines directly with certain organic
bases, such as aniline, toluidine, etc., and this reaction
has been recommended for the removal of cyanogen
from mixed gases ; but, as has been pointed out by

1 B. Radziszewski, Ber. 23, 355.



CYANOGEN AND THE CYANOGEN HALOIDS 5

M. Loeb, 1 both carbon monoxide and dioxide would
react, decomposing the compound.

By passing cyanogen into a 40 per cent, aqueous
solution of azoimide, cyanotetrazol (tetrazole 5
carbonylonitrile), C 2 HN 5 , is produced. 2 The product
melts at 99, forming a reddish-brown liquid, and
yields ammonia quantitatively when boiled with
caustic potash solution ; the silver salt, AgC 2 N 5 , and
the barium salt Ba(C 2 N 5 ) 2 3-JH 2 O, have been prepared.

As cyanogen may be obtained by heating oxamide
with phosphorous pentoxide, it has been considered as
the nitrile of oxalic acid with the formula :

N = C -C==N.

According to Dixon and Taylor, 3 the formula
should be :



u



PARACYANOGEN, (CN)*. When the dry cyanide
of a noble metal, such as the silver, or mercury salt is
ignited, cyanogen is evolved with liberation of the
metal ; part of the cyanogen, however, at the tempera-
ture necessary for the reaction, polymerizes to form a
dark brown substance called paracyanogen : a larger
yield of the compound is obtained when the silver
cyanide is ignited than when the mercury salt is used.
It is also obtained when cyanogen gas is heated under
pressure in a closed vessel, the amount formed varying
with the temperature and pressure ; but high pressure,
although favouring the formation of paracyanogen,
also tends to decompose the cyanogen into its elements.

Paracyanogen is a dark, brownish - black com-
pound, insoluble in water or alcohol, but soluble in
concentrated sulphuric acid in the cold, from which
it may be precipitated unchanged by dilution with

1 J.C.S., liii. 812.

2 E. Oliveri-Mandola and T. Passalaeque, Gazetta (1911),
41, ii. 430 ; J.C.S. (1912), i. 144.

3 T.C.S. (1913), 982.



6 THE CHEMISTRY OF CYANOGEN COMPOUNDS

water. It may be reconverted into normal cyanogen
gas by heating to about 860 C. in a current of inert
gas, such as nitrogen or carbon dioxide ; heated in a
current of hydrogen, it is converted into hydrocyanic
acid, ammonia, and carbon.



CYANOGEN HALOIDS

CYANOGEN BROMIDE, CNBr. i. This body was
discovered by Serullas in 1827, 1 and is easily produced
by the action of bromine on an aqueous solution of
hydrocyanic acid or a soluble cyanide :

HCN + Br 2 = HBr + CNBr ;
or NaCN + Br 2 = NaBr + CNBr.

2. It may also be produced by the electrolysis of a
solution of sodium bromide and cyanide.

3. By heating a mixture of sodium cyanide, sodium
bromide and manganese dioxide with sulphuric acid : 2

NaBr + NaCN + MnO 2 + 2H 2 SO 4 =
CNBr + Na 2 SO 4 + MnSO 4 + 2H 2 O.

4. And by heating a mixture of sodium thiocyanate
and sodium bromide with an oxidizing agent :

NaBr + NaCNS + 2O 2 = Na 2 SO 4 + CNBr.

A mixture of the two salts is run into the oxidizing
agent kept .at 100 C., which may, for example, be a
solution of a mixture of nitric and sulphuric acid, but
containing 20 per cent, of nitric acid.

The most convenient mode of preparing the com-
pound is to add the bromine to a cooled solution of
potassium cyanide ; when the reaction is complete the
mixture is gently warmed, and the sublimed bromide
condensed in a receiver surrounded by freezing mixture.
This process has been slightly modified by R. Scholl, 3
who recommends the following proportions, whereby a
90 per cent, yield is obtained ; a solution of 65 grams
of potassium cyanide in 120 c.c. of water are cooled

* Ann de Phys. (2), 34, 100, 35, 294.

z E.P., 2660 (6.2.95). 3 Ber. (1896), 29, 1822-25.



CYANOGEN AND THE CYANOGEN HALOIDS 7

to o C., and slowly added to 150 grm. of bromine also
cooled to o C., and the liquid agitated while mixing ;
the product is then distilled at 60 to 70 C., and the
evolved cyanogen bromide condensed.

Cyanogen bromide is thus obtained in long, delicate
prisms which slowly change to cubes ; it is very
volatile, and its vapour, which has a pungent odour,
attacks the eyes and nose, causing tears ; it is exceed-
ingly poisonous, and its vapour dangerous to inhale,
one grain of the solid being sufficient to kill a rabbit
instantly. The compound is very soluble in water
and alcohol, and it also dissolves in cold strong sul-
phuric, nitric, or hydrochloric acid without decomposi-
tion, and combines with ammonia, forming a mixture
of ammonium bromide and cyanamide :

CNBr + 2NH 3 = NH 4 Br + H 2 CN 2 .

With aqueous sulphurous acid decomposition occurs
with formation of sulphuric, hydrobromic, and hydro-
cyanic acids :

H 2 S0 3 + CNBr + H 2 O = H 2 SO 4 + HCN + HBr.

Aqueous caustic alkalis convert it into a cyanide,
bromide, and a bromate :

3CNBr + 6KOH = 3 KCN + 2KBr + KBrO 3 + sH 2 O.

Cyanogen bromide melts at 52 C. and boils at 61 C.

Antimony heated in its vapour yields antimony
bromide and cyanogen ; while metallic mercury de-
composes the aqueous solution in a similar manner,
with production of mercuric bromide and cyanogen.

When treated with hydrogen sulphide, hydrothio-
cyanic, and hydrobromic acids are formed :

CNBr + H 2 S = HCNS + HBr.

But if the reaction takes place in the presence of
hydrochloric acid, hydrocyanic and hydrobromic acids
are formed together with free sulphur : 1

CNBr + H 2 S = HCN -f HBr + S.
1 A. E. Dixon and Taylor. P.C.S. (1913), 90.



8 THE CHEMISTRY OF CYANOGEN COMPOUNDS

With alkaline sulphides the corresponding bromide
and thiocyanate are formed. 1

When cyanogen bromide is treated with thiocar-
bamide and sodium bicarbonate, cyanamide together
with a bromide and thiocyanate are formed, with
evolution of carbon dioxide, but no cyanide. The
reaction may be expressed thus :

CNBr + CSN 2 H 4 = HBr + HCNS + H 2 CN 2

The reaction proceeds differently in the presence of
strong acids, hydrocyanic and hydrobromic acids
being formed and a salt of formamidine disulphide ;
but in neutral solutions both of these reactions take
place. 2

Cyanogen bromide is slowly decomposed by water.

Cyanogen bromide is sometimes used in conjunction
with a dilute cyanide solution in the process of Sulman
and Teed for the treatment of refractory gold ores,
such as the telluride gold ores of Western Australia.
For this purpose it is usually made on the spot owing
to the extreme difficulty of transporting the material.

From a study of the reactions of these compounds,
Gutmann 3 has suggested the structural formula :



where X= chlorine, bromine or iodine.

POLYMERIC CYANOGEN BROMIDE, or CYA-
NURIC BROMIDE, (CN) 3 Br 3 , is known, and may be
prepared in good yield by the action of moist hydro-
bromic acid on a solution of cyanogen bromide in
benzene. It combines with 10 per cent, hydrazine to
form cyanuric trihydrazide ; with an ethereal solution
of phenylhydrazine, cyanuric triphenylhydrazide is
formed ; and with carbamide it unites at 130 140 C.
to form tricar bamylmelamine. 4

1 Gutmann, Ber. (1909), 42, 3628.

2 A. E. Dixon and Taylor, T.C.S. (1913), 980.

3 Ber.. 42, 3623.

4 E. von Meyer, /. pr. Chem. (1910) [ii], 82, 321-38.



CYANOGEN AND THE CYANOGEN HALOIDS 9

CYANOGEN CHLORIDE, CNC1, was discovered by
Berthollet l and investigated by Gay Lussac 2 and
others, who demonstrated its true nature and pro-
perties.

It is prepared by passing chlorine into aqueous
hydrocyanic acid, or by allowing chlorine to act on
moist mercuric cyanide in the dark.

The gas was prepared by Gay Lussac, by passing
chlorine into an aqueous solution of hydrocyanic acid,
but is more generally prepared by leaving moist
mercuric cyanide in contact with chlorine in a large
flask in the dark, and at the ordinary temperature,
the excess of chlorine being removed by agitation with
metallic mercury, and the gas dried by passing over
fused calcium chloride.

It may also be prepared by the action of hydro-
chloric acid on a mixture of bleaching powder and an
alkaline cyanide ; 3 and in a similar manner to the
preparation of the bromide, by the action of oxidizing
agents on a mixture of an alkali metal chloride and
thiocyanate ; 4 or by electrolysis of a mixture of
sodium cyanide and chloride. 5

Cyanogen chloride is a gas with a powerful odour ;
it attacks the eyes and is excessively poisonous and
the greatest care should be taken in its preparation.
It has a specific gravity of 2*12, and when cooled to
below 6 C. it solidifies in long transparent prisms.
It is soluble in water, alcohol, and ether ; at 20 C.
water dissolves twenty-five times its volume of the
gas, alcohol about one hundred times its own volume,
and ether about fifty times its volume.

When kept in sealed tubes for some time the gas
gradually polymerizes to solid cyanuric chloride, and
when treated with alkalis it is converted into a chloride
and a cyanate. Antimony heated in the gas yields
antimony chloride and free cyanogen ; the gas also

1 Ann. Chem., I, 35. 2 Ann. Chem., go, 200.

3 E. Morgan, E.P., 2660 (6.2.95). 4 E.P., 9710 (26.5.00).
6 E.P., 2660 (6.2.95).



io THE CHEMISTRY OF CYANOGEN COMPOUNDS

combines with certain anhydrous chlorides to form
compounds such as

Sb 2 Cl 5 CNCl ; BClgCNCl ; FeCl 3 CNCl, etc.

Treated with an alkali sulphide, a thiocyanate and
chloride are formed. 1 With sodium sulphite, the
cyanide, chloride, and sulphate of sodium are formed. 2

Solid cyanogen chloride or cyanuric chloride, (CN) 3 C1 3 ,
is a polymeric modification of cyanogen chloride, and
was first discovered by Serullas in 1827, 3 who con-
sidered it to be cyanogen bichloride, but its true
composition was afterwards demonstrated by Liebig.

Cyanuric chloride is formed when gaseous cyanogen
chloride is kept for some time, the polymeric change
being considerably hastened by sunlight ; it was
prepared by Liebig, by heating potassium thiocyanale
in chlorine gas :

3KCNS + 6C1 2 = 3KC1 + (CN) 3 C1 3 + 3SC1 2 .

It may also be prepared by the action of phosphorous
pentachloride on dry cyanuric acid :

H 3 C 3 N 3 3 + 3 P 2 C1 5 = (CN) 8 (C1), + 3P 2 OC1 3 + 3 HC1.

Cyanuric chloride is obtained in monoclinic needles,
which melt at 140 C. to a colourless liquid and on
further heating boils at 190 C. ; the vapour has an
odour suggesting chlorine, and like the other cyanogen
haloids it is exceedingly poisonous, and attacks the
eyes, causing tears.

The compound is slightly soluble in water. The
solution decomposes slowly in the cold with formation
of hydrochloric and cyanuric acids :

(CN) 3 C1 3 + 3H 2 = (CN) 3 (OH) 3 + 3 HC1.

The rate of decomposition increases as the temperature
rises : it dissolves readily in alcohol and ether.

CYANOGEN IODIDE was discovered by Sir Hum-
phry Davy in i8i6. 4 It cannot be prepared by the

1 Gutmann, Ber., 42, 3623. 2 Gutmann, I.e.

3 Ann. Ch. Phys. [2], 35, 291, 337.

4 H. Davy, Gilb. Ann., 54, 384.



CYANOGEN AND THE CYANOGEN HALOIDS n

direct union of cyanogen and iodine, but may be
obtained, by the action of the iodine on an aqueous
solution of a cyanide ; the iodine is added to a strong
aqueous solution of potassium cyanide, the mixture is
then gently warmed and the sublimed cyanogen iodide
condensed in a cooled receiver. The action of iodine
on aqueous hydrocyanic acid only results in the
conversion of a portion of the cyanogen into the
iodide, the reaction :

HCN + I 2 ^CNI +HI

being a reversible one, a larger proportion is obtained
by dilution or by increasing the temperature.

It is best prepared by thoroughly mixing one part
of iodine with two parts of silver cyanide in a retort
which is then gently heated, and the vapours conducted
into a cooled receiver, where it crystallizes in white
crystals. Mercuric cyanide may be substituted for
the silver salt, but the resulting cyanogen iodide
should be purified by resublimation on the water-bath.

Cyanogen iodide may also be prepared by most of
the general methods described under cyanogen bromide
and chloride, by which it is usually obtained with
greater ease and in better yields.

Cyanogen iodide crystallizes in fine long white
needles and is exceedingly poisonous. Like the other
cyanogen haloids it attacks the eyes and nose. The



Online LibraryHerbert E WilliamsThe chemistry of cyanogen compounds and their manufacture and estimation → online text (page 1 of 35)