Sartori The War Gases Chemistry and analysis

50 ml. cyanide solution are added from the tap-funnel at such a rate that there is always an excess of iodine present. The current of chlorine is then stopped and a little more sodium cyanide is added. The reaction product is then extracted with ether, the ethereal extract dried over calcium chloride and the ether distilled off. A crystalline residue of cyanogen iodide remains.

Yield 80-85% of theoretical.

PHYSICAL AND CHEMICAL PROPERTIES

Cyanogen iodide forms white crystals which gradually decom-

Cyanogen iodide reacts with hydriodic acid much more readily than the chloride and bromide, iodine being liberated.

Sulphurous acid is oxidised to sulphuric acid : 2CNI + H2SO3 + H2O = H2SO4 + 2HCN + I2

and sulphur is liberated from sulphides.4

It reacts quantitatively with sodium arsenite according to the equation 5 :

CNI + Na3AsO3 + aNaOH = NaCN + Na3As04 + Nal + H8O.

It also reacts with hydrochloric acid, forming iodine mono-

chloride :

CNI + HC1 = 2HCN + IC1,

and with hydrobromic acid liberating bromine and iodine : 2CNI + 2HBr = 2HCN + I2 + Bra.

It does not react with silver nitrate. On treatment of an aqueous solution of cyanogen iodide with potassium hydroxide and subsequent addition of ferrous and ferric salts and hydrochloric acid, a precipitate of Prussian blue is obtained.6

The reactions of cyanogen iodide with many other substances have been studied.7 From these it has been found that when treated with reducing agents its iodine is completely removed, while other reagents which normally remove iodine from iodides do not affect it.

7-2

/Br

C6H5-CH<; xBr

Bromobenzyl cyanide was prepared by Reimer 1 in 1881, but it was not isolated in the pure state until 1914 .It was employed as a war gas by the French in the last years of the war, usually in solution in chloropicrin.

According to American experiments made since the war, this compound is to be considered as one of the most efficient of the war gases because of its great persistence and its high lachrymatory power.

It is also known as " Camite " (France), and by the symbol " CA " (America).

PREPARATION

Bromobenzyl cyanide was prepared by Reimer by the action of bromine on benzyl cyanide heated to 120° to 130° C.

This compound may be prepared either by the action of cyanogen bromide on an alcoholic solution of benzyl cyanide in presence of sodium ethylate, according to the equation 2:

Cn- + NaBr+C2H5OH

or else, by a method similar to that used by Reimer, by the action of bromine vapour on benzyl cyanide heated simply to 105° C., or to 120° C. while the gas mixture is exposed to the light of a 1,000 c.p. Osram lamp. By this method a much higher yield of bromobenzyl cyanide is obtained.3

LABORATORY PREPARATION 4

In preparing this substance, it is advisable to start with benzyl bromide and first convert this into the cyanide, which is afterwards brominated.

60 gm. benzyl bromide, 27 gm. potassium cyanide, 45 gm. ethyl alcohol and 25 gm. water are placed in a flask fitted with a reflux condenser and boiled for 4 hours. The mixture is then extracted with ether, the ether extract separated and dried over calcium chloride, the ether distilled off and the residue itself then

1REIMER, Ber., 1881,14, 1797 ; STEINKOPF, Ber., 1920, 53, 1146 ; NEKRASSOV,

/.prakt. Chem., 1928, 119, 108.

2VONBRAUN, Ber., 1903, 36, 2651.

3STEINKOPF and coll., Ber., 1920, 53, 1144.

' NEKRASSOV, op. cit.

possibly refers to the technical product.

It is insoluble in water, though it easily dissolves in many organic solvents (alcohol, benzene, carbon disulphide, acetic acid, acetone, ether, chloroform, carbon tetrachloride, etc.). It is also soluble in several of the other war gases, such as phosgene, chloropicrin, etc. Because of this property, it may be used together with these war gases so as to attain a more complete range of effects.

Bromobenzyl cyanide decomposes on heating : at 160° C. the decomposition commences with the formation of dicyanostilbene and hydrobromic acid :

It is highly resistant to chemical and atmospheric agencies. Water and humidity decompose it only very slowly. Cold sodium hydroxide solution acts similarly, though on prolonged boiling almost quantitative decomposition takes place with an aqueous solution of sodium hydroxide. A 20% solution of sodium hydroxide decomposes two and a half times its own weight of the cyanide. Alcoholic potash decomposes it even in the cold.

When treated with some of the most vigorous oxidising agents, such as potassium or sodium chlorate, potassium permanganate, peroxides, etc., it is attacked only slowly. Owing to this stability to humidity and to chemical reagents, as well as its low vapour pressure, this substance has a high persistence, especially in suitable meteorological conditions such as cold, dry weather.3

Bromobenzyl cyanide in alcoholic solution reacts with sodium sulphide to form dicyanobenzyl sulphide :

insoluble in water, but soluble in the common organic solvents. On boiling bromobenzyl cyanide with an aqueous-alcoholic

solution of sodium thiosulphate, the sodium salt of cyanobenzyl thiosulphuric acid is formed :

C6HBCH(CN)Br + Na2S203 = C6H5CH(CN)S2O3Na + NaBr.

1 FERRI and MADESANI, Giornale Medicina Militare, 1936, Part I,

with dichloroethyl sulphide in order to mask the odour of the latter.

Phenyl carbylamine chloride is usually prepared by the chlorination of phenyl isothiocyanate x :

/Cl

C6H8-N=C=S + 2C12 - CeH5-N=C( + SC12

Cl

Various methods have been employed for preparing phenyl isothiocyanate. It may be obtained, for instance, from carbon disulphide and aniline, which react to form thiocarbanilide in presence of alkali hydroxides :

/NH-C6H5 CS2 + 2 C6H5-NH2 = H2S + S=C<

NNH-C8H6

and this on heating with acid decomposes into aniline and phenyl isothiocyanate :

NH-C6H6

T^ «« -*• C6HS-NH2 + C6HS-N=C=S -NH-L6H5

Another rather similar method is to treat carbon disulphide with aniline in presence of lime. Calcium phenyl dithiocarbamate is first formed, according to the equation :

On treating this with an alkaline zinc chloride solution it decomposes with production of phenyl isothiocyanate :

S

(C6H5-NH-C-S)2Ca -> Ca(SH)2 + 2 C6H5-N=C=S

This second method of preparation was employed by the Germans during the war.

LABORATORY PREPARATION 2

In the laboratory, phenyl isothiocyanate is first prepared from aniline and carbon disulphide and the product then chlorinated.

1 SELL and ZIEROLD, Ber., 1874, 7, 1228.

2 NEKRASSOV, op. cit. ; NEF,Ann., 1892, 270, 274.

product reaches the value of 1-45 (about 24 hours). The sulphur chloride is separated by distillation, when the phenyl carbylamine chloride remains as a residue ; it is transferred to containers for storage. Yield 90%.

PHYSICAL AND CHEMICAL PROPERTIES

Phenyl carbylamine chloride is an oily liquid which is only slightly volatile. It is pale yellow in colour and has an onion-like odour. At ordinary pressure it boils at 208° to 210° C.,1 and at

hydrogen sulphide even at ordinary temperature, forming phenyl isothiocyanate :

In contact with mild oxidising agents like mercuric oxide, silver oxide, etc., phenyl isocyanate is formed :

/OH

C6H5-N=C=O + H20 = C0< NNH-C6H5

NH-C6H5

On heating with aniline it reacts vigorously, forming triphenyl guanidine (Nef).

1 ELY and coll., /. Am. Chem. Soc., 1922,44, 2896.

204 CYANOGEN DERIVATIVES

Phenyl carbylamine chloride, even when diffused in the air in the vapour state (at concentrations above 4%), produces with the Grignard reagent (see p. 248) a turbidity like that obtained with dichloroethyl sulphide (Hanslian).

In contact with steel it decomposes slowly.

Owing to its high boiling point it is classed as a very persistent war gas, but found only limited employment in the last war.

The irritant power of phenyl carbylamine chloride is very great; according to Miiller 3 mgm.are sufficient to produce irritation. The limit of insupportability is 30 mgm. per cu. m. of air. The mortality-product is 3,000 according to Miiller and 5,000 for 10 minutes' exposure according to Prentiss.

Analysis of the Cyanogen Compounds

DETECTION OF HYDROCYANIC ACID

Of the various methods proposed for the detection of hydrocyanic acid, the following are recommended :

The Prussian Blue Reaction. On addition to an alkaline solution of hydrocyanic acid of a few ml. of ferrous sulphate solution and of ferric chloride solution, then shaking and warming, a blue precipitate of ferric ferrocyanide appears on acidification with hydrochloric acid. In presence of only a trace of hydrocyanic acid, only a greenish-blue colouration appears, due to the formation of a colloidal suspension of the ferric ferrocyanide. On standing (sometimes for as long as 12 hours) the suspension settles to blue floes, leaving the supernatant solution colourless.

This reaction is specific for hydrocyanic acid and is quite sensitive, detecting 5 mgm. per cu. m. of air according to Kolthoff.1 The Prussian blue reaction may be rendered more convenient in use by employing a reaction paper. For this purpose Ganassini's 2 paper is strongly recommended. It is prepared by immersing a strip of filter paper, just before use, in a mixture of 10 ml. 10% ferrous sulphate solution (containing a trace of ferric salt) and 20 ml. of an alkaline solution of Rochelle salt (30 gm. Rochelle salt, 10 gm. potassium hydroxide and 100 ml. water). This paper should be exposed first to the atmosphere containing hydrocyanic acid and then to hydrochloric vapour,

when it becomes greenish-blue.

The Ferric Thiocyanate Reaction. This test is carried out on a solution of the material to be examined ; if the sample is gaseous, a solution may be obtained by bubbling it through an alkaline

1KOLTHOFF, Z. anal. Chem., 1918, 57, i.

2GANASSINI, Bull. soc. Medico-chirurg. di Pavla, 1910.