Sartori The War Gases Chemistry and analysis

3i6 ARSENIC COMPOUNDS

further purified by distillation under reduced pressure. The yield of diphenyl cyanoarsine by this method is 80-90% of the theoretical.

Steinkopf's method * gives higher yields :

10 gm. of diphenyl arsenious oxide and 6 gm. anhydrous hydrocyanic acid (i.e., five times the theoretical amount) are placed in a glass tube, which is then sealed in the flame. The mixture is then heated for 2 hours at 100° C. The residue is then extracted with ether after cooling, the ether distilled off and the product which remains fractionally distilled at reduced pressure (13-15 mm.).

INDUSTRIAL MANUFACTURE

In Germany, according to Norris, diphenyl cyanoarsine was prepared by treating diphenyl chloroarsine with a concentrated aqueous solution of potassium cyanide and heating to 60° C. A 5% excess of the cyanide was employed and the reaction mixture stirred continuously.

PHYSICAL PROPERTIES

Diphenyl cyanoarsine forms colourless prisms with an odour of mixed garlic and bitter almonds. It melts at 35° C. (Sturniolo), at 32° to 34° C. (McKenzie), at 31-5° C. (Steinkopf). It boils at 213° C. at 21 mm. mercury pressure and at 200° to 201° C. at 13-5 mm. At 760 mm. the boiling point is calculated from the vapour pressure curve to be 377° C.2 The specific gravity is 1-45.

The vapour pressure is very low and at 20° C. is only 0-0002 mm. mercury. The volatility at the same temperature is 0-1-0-15 mgm. per cu. m. of air.

Diphenyl cyanoarsine is sparingly soluble in water, but dissolves readily in alcohol, benzene, chloroform, ether and ligroin.

CHEMICAL PROPERTIES

Like diphenyl chloroarsine, diphenyl cyanoarsine is not very stable and its arsenic atom has a tendency to change from the trivalent to the pentavalent state.

Water. Atmospheric moisture decomposes diphenyl cyanoarsine slowly, hydrocyanic acid and diphenyl arsenious oxide being formed :

2(C6H6)2AsCN + H20 = [(C6H6)2As]20 + 2HCN.

1STEINKOPF, Ber., 1921, 54, 1460.

2HERBST, Kolloidckem. Beihefte, 1926, 23, 340.

DIPHENYL CYANOARSINE : PROPERTIES 317

This decomposition takes place more rapidly with hot water, or with aqueous or alcoholic solutions of the alkalies.

The conversion of diphenyl cyanoarsine into diphenyl arsenious oxide may be attained also by steam distillation. The oxide consists of crystals which are sparingly soluble in water, but soluble in alcohol, ether, chloroform ; the melting point is 92° to 93° C.

Chlorine. Diphenyl cyanoarsine in benzene solution is converted by chlorine into a compound melting at 115° C. which, according to McKenzie, appears to be anhydride of tetraphenyl tetrachloro arsenic acid, [(C6H5)2AsCl2]2O. The reaction is as follows :

(C6H5)2AsCN + Q, = (C6Hs)2As • CN • C12

(C6H5)2AsCN • C12 + H80 = (C6H5)2AsCl2 • OH + HCN

2 (C6H5)2AsCl2 • OH -* H2O 4- fC^HJjAs • Cl2-O-Cl2As-(C6H8)a

This compound fumes in air and from its aqueous solution diphenyl arsenic acid separates on cooling.

Oxidising Agents. When diphenyl cyanoarsine, cooled in a water-bath, is treated with nitric acid, with 2% hydrogen peroxide or with bromine water, it is oxidised to diphenyl arsenic acid, (C6H5)2AsOOH which forms acicular crystals melting at 175° C. The alkali salts of this acid are readily soluble ; the iron compound is a white powder which decomposes on heating.1

Methyl Iodide. By the action of methyl iodide on diphenyl cyanoarsine, by heating in a closed tube for 6 hours at 100° C., diphenyl methyl arsonium iodide and triiodide are obtained. The latter crystallises in violet needles which melt at 69° C. and are insoluble in water and in ether.

Diphenyl cyanoarsine has such a low vapour pressure that it must be diffused as a particulate smoke in the air, in the same way as diphenyl chloroarsine. Its behaviour to active carbon is due to this state of extreme subdivision. Layers of animal or vegetable fibres, properly treated and washed, form an efficient filter.

The minimum concentration of diphenyl cyanoarsine detectable by odour is o-oi mgm. per cu. m. according to Lindemann and 0-005 mgm. per cu. m. according to Meyer.

A normal man can support a maximum concentration of 0-25 mgm. per cu. m. of air for not more than 1-2 minutes (Flury).

1 G. STURNIOLO and G. BELLINZONI, Boll. chim. farm., 1919, 58, 409 ; Gazz, chim. ital., 1919, 49, 326.

ARSENIC COMPOUNDS

The mortality-product is 4,000 according to Muller, or for 10 minutes' exposure according to Prentiss, 10,000.

(C) HETEROCYCLIC ARSINES

The study of the heterocyclic arsines (i.e., those containing the atom of arsenic in the nucleus) may be said to have commenced only during the war of 1914-18 and led to the discovery of substances whose military value is equal, or according to some authorities superior, to that of the aromatic arsines. Among these substances " Adamsite" has claimed most interest, particularly because of the simplicity of its method of preparation.

This substance, also known as " diphenylamine chloroarsine," has the following structure :

which has been confirmed by its mode of formation from arsenic trichloride and diphenylamine :

HN(	CK	CDv
	+	>As-Cl = HN'CD)AS-CI + 2 HCI

By analogy with other classes of substances of similar constitution, such as phenazine (I) and phenoxazine (II) :

H

N N

/\/\/\

\x\x\

N

THE HETEROCYCLIC ARSINES

319

it may be accurately described as 10 chloro 5-10 dihydrophenarsazine, or, more briefly, as phenarsazine chloride.

Various analogous and homologous compounds of phenarsazine chloride have been studied.1 Among the more important may be mentioned phenarsazine bromide, obtained by the action of arsenic bromide on diphenylamine,2 phenarsazine iodide 3 and phenarsazine fluoride* as well as phenarsazine cyanide.5 All these compounds have toxic properties similar to those ofphenarsazine chloride.6

Substances of analogous types to that of the phenarsazine

derivatives have also been prepared.	Lewis 7 first, and later
Turner 8 prepared phenoxarsine chloride	(6 chlorophenoxarsine) :

Kalb 9 prepared arsanthrene chloride :

CI

As

/\/\/\

These substances, which are very similar in properties to phenarsazine chloride, have the drawback that their preparation is in each case very laborious.

1 BURTON and GIBSON, /. Chem. Soc., 1924, 2275 ; 1926, 464; C. NENITZESCU,

Antigai, 1929, Nos. 2-3.
2	BAYER, D.R.P. 281049.
*	RASUVAJEV and BENEDIKTOV, Ber,, 1930, 63, 346.
1	GIBSON and coll., Rec. trav. Chitn., 1930, 49, 1006.
5	GRYSKIEWICZ and coll., Bull. soc. chim., 1927, 41, 1323.
6	GIBSON and JOHNSON, /. Chem. Soc., 1931, 2518.
7	LEWIS, /. Am. Chem. Soc., 1921, 43, 892.
8	TURNER, /. Chem. Soc., 1925, 127, 544.
»	KALB, Ann., 1921, 423, 63.

320 ARSENIC COMPOUNDS

Phenarsazine Chloride (Adamsite)	(M.Wt. 277-5)
/CgHjv
HN<	>AsCl

\C6H/

According to Hanslian this substance was prepared in Germany by Wieland 1 in 1915, and independently in January, 1918, by Adams (whenceits name of Adamsite). However, the recognition of the importance of this substance as a war gas must be attributed solely to the English and Americans who studied its chemical and biological properties.

PREPARATION

Wieland 2 obtained phenarsazine chloride by treating diphenylamine with arsenic chloride :

(CaH5)2NH + AsCL, = NH(C6H4)2AsCl + aHCl.

It may also be obtained by the following methods :

(a)By heating diphenyl hydrazine with arsenic trichloride.3

(b)By boiling aniline with arsenic trichloride, then adding sodium hydroxide, and treating the oxide obtained with

hydrochloric acid.4

(c) By treatment of fused diphenylamine with concentrated hydrochloric acid and then mixing with arsenious oxide 5 :

(C6H5)2NH -f HC1 - (C6H5)2NH • HC1

2 (C6H5)2NH • HC1+ As,O3 = 2 NH(C6H4)2AsCl + 3 H2O

LABORATORY PREPARATION 5

Contardi's method is used : this involves the treatment of diphenylamine with arsenious oxide :

42 gm. diphenylamine and 21 ml. hydrochloric acid (S.G. 1-19) are placed in a porcelain dish of about 300 ml. capacity and heated with constant stirring until all the water has been driven off. Diphenylamine hydrochloride is obtained as a white powder ; it is dried for 2-3 hours at 50° to 60° C. It is mixed with 25 gm. arsenious oxide and melted with continuous stirring. When the whole mixture is molten, the temperature is gradually raised ; at 140° C. the reaction becomes vigorous and water vapour is evolved. After 3-4 hours the temperature rises to 200° C. and

1	Elberfelder Farbenfabrik. Bayer, D.R.P. 281049.
2	WIELAND and RHEINHKIMER, Ann., 1921, 423, 12.
3	LEWIS and HAMILTON, /. Am. Chem. Soc., 1921, 43, 2218.
4	BURTON and GIBSON, /. Chem. Soc., 1926, 450.
1	CONTARDI, Giorn. Chim. Appl., 1920, 1, n.

PHENARSAZINE CHLORIDE: MANUFACTURE 321

the evolution of water vapour ceases : the reaction may then be considered as complete. The product obtained is purified by crystallisation from xylene. Yield is almost theoretical.

INDUSTRIAL MANUFACTURE

American Method. The process used by the Americans at Edgewood Arsenal for the manufacture of phenarsazine chloride is based on the reaction of diphenylamine with arsenic chloride :

(C6H6)2NH + AsCl3 = NH(C6H4)2AsCl + 2HC1.

Operating Details. 642 kgm. diphenylamine are first heated to 150° C. in a large jacketed kettle fitted with an agitator and a reflux condenser. 730 kgm. arsenic trichloride (that is, 10% excess over theoretical) are added and the heating continued for 5 hours. During the course of the reaction, the temperature rises to 250° C., and large quantities of hydrochloric acid are evolved. This passes through the condenser and is absorbed in water in a special absorption tower. At the end of the reaction, the product obtained is transferred to a vessel containing water where it is washed, then centrifuged and dried at 30° C. Yield

80%.

Italian Method. During the war, Professor Contardi proposed a method of preparation much more simple than the American process just described. In studying a newprocess for manufacturing diphenylamine, he observed that the hydrochloride of this base is completely dissociated into hydrochloric acid and diphenylamine when heated to slightly over 100° C. He studied the possibility of using this reaction to prepare phenarsazine chloride by starting from arsenious oxide and diphenylamine hydrochloride, instead of arsenic trichloride and diphenylamine. The equation of this reaction is as follows :

/C6HA

2 (C6HS)2NH-HC1 + As2O3 = 3 H20 + 2 HN( />As • Cl C6H4

In order to prepare phenarsazine chloride by this method it is sufficient to mix diphenylamine hydrochloride with arsenious oxide and heat to 130° C. After the mixture is melted, the temperature is gradually raised to 200° C. When the evolution of water ceases, the reaction is complete. Yield 95% of the theoretical.

Fig. 18 shows a diagram of the plant proposed by Professor Contardi for the industrial preparation of phenarsazine chloride.

322 ARSENIC COMPOUNDS

The reaction is carried out in the cast iron kettle A, which holds 7-5 litres and is fitted with the helical agitator JB which imparts an ascending motion to the mass, so that a homogeneous distribution of the particles in the liquid is obtained. The kettle is closed at the top with a lid, in the centre of which is the agitator gear, and which also has a charging hole C for the diphenylamine hydrochloride and arsenious oxide. Above this hole a hopper is

	fitted.			A	stuffing - box
	also		passes		through				the
	lid,		supporting						the
	thermometer					T		which
	indicates the temperature
	of	the		reaction		mixture.
	At the bottom of the
	kettle is a tube of 10 cm.
	diameter closed							with a
	plug		valve		D;		through
	this			the	product				is
	discharged.				The			kettle
	is	surrounded					by		the
	walls			L and		is		heated
	by means of the three
	heating coils f, f,							f".
		With a battery of four
	kettles of this description,
	it is possible to make 6
	tons			of	phenarsazine
	chloride by				this			method
	in 24 hours.
FIG. 18.	This			process				differs
	from			the	A m e r i c a n
method more particularly in saving a considerable					proportion of

the hydrochloric acid (more than two-thirds) and of the arsenious oxide, and also makes it unnecessary to prepare arsenic trichloride. Moreover, all the difficulties attendant on the necessity for utilising or disposing of the large quantities of arsenical products which are invariably obtained in the American process are obviated.

PHYSICAL PROPERTIES

Phenarsazine chloride in the crude state is a crystalline solid, dark green or sometimes brown in colour. It may be obtained in the pure condition by crystallisation, or, better, by vacuum sublimation. It is then of a canary-yellow colour with a melting

PHENARSAZINE CHLORIDE: PROPERTIES 323

point of 189° to 190° C. (Burton and Gibson), 191° to 193° C. (Rasuvajev), 192-5° (Tanner),1 or 193° to 195° C. It is practically odourless at ordinary temperatures. It has been shown recently that phenarsazine chloride, like diphenyl chlorarsine, can exist in twomodifications :

A stable orthorhombic form which melts at 195° C., and a metastable form which is partly monoclinic and melts at 186° C. and partly triclinic, melting at 182° C.2

The boiling point calculated from the vapour tension curve

is 410° C.
The specific heat is 0-268 calorie and the	heat of volatilisation
54-8 calories.
The volatility at ordinary temperatures	is low : at 20° C. it
is only 0-02 mgm. per cu. m. of air.

The vapour tension at various temperatures is given in the following table :

Temperature	Vapour Tension
°C	MM. MERCURY
o	5 x io-18
20	2 X IO-13
40	2 X IO-11
100	2 X 10-'
150	0-003
The specific gravity at	20° C. is 1-648. It is practically

insoluble in water, and sparingly soluble in the common organic solvents such as benzene, xylene, etc., with which it forms molecular compounds of great stability. It is also insoluble in phosgene and only slightly soluble at the ordinary temperature in carbon tetrachloride. It dissolves in concentrated sulphuric acid with an intense cherry-red colour, and in arsenic trichloride to give a dark green solution.

CHEMICAL PROPERTIES

Water. Phenarsazine chloride, unlike the arsenic compounds previously described, is slowly hydrolysed by water. On adding a little water to the alcoholic solution, a turbidity appears which consists of phenarsazine oxide.3

Bromine. By the action of bromine on phenarsazine chloride in acetic acid solution, a brominated derivative is not obtained,

1 TANNER, U.S. Pat., 1557384/1922.

3 FISCHER, Mikrochemie, 1932, 12, 257.

8 KAPPELMEYER, Rec. trav. Chem., 1930, 49, 82.

324 ARSENIC COMPOUNDS

but the molecule is decomposed and tetrabromodiphenylamine is formed 1:

HN( * 4)AsCl + 4 Brz = HN(C6H3Br2)2 -f AsBr3 + HC1 + HBr NC,H/

Tetrabromodiphenylamine forms lustrous crystals melting at 185° to 186° C.

Hydrochloric Acid. When phenarsazine chloride is treated with gaseous hydrochloric acid at 160° C. it decomposes, forming arsenic trichloride and diphenylamine as follows 2 :

= NH(C6H6)2 + AsCl3

C6H

Hydriodic Acid. On treatment with aqueous hydriodic acid on the water-bath, phenarsazine chloride forms diphenylamine as in the previous reaction 3 :

AsCl -f 2 HI = NH (C6H5)2 + AsClI2

Alkalies. Phenarsazine chloride reacts with the alkalies to form phenarsazine oxide, according to the following equation :

/C6HA		/C6H4\	>As)2O
2 NH(	)As - Cl + H2O = 2 HC1+ (HN(
XC,H/		NC6H/

This substance forms colourless leaflets with a melting point above 350° C. and is soluble with difficulty in most of the organic solvents. It reacts on heating with alcohols and phenols, and has a vigorous irritant action.

Ammonia. When a current of dry ammonia is passed through a solution of phenarsazine chloride in xylene, a compound of the following composition is obtained :

/C6H4\

(HN\C6H/AS)3N

This is triphenarsazine amine which melts at 295° to 300° C. Oxidising Agents. Oxidising agents react with phenarsazine

chloride, converting the arsenic atom from the trivalent to the pentavalent condition. Hydrogen peroxide in acetic acid

1 L.ELSON and C.GIBSON,/.Chem.Soc., 1929, 1080.

1	O. SEIDE and GORSKY,Ber., 1929, 62, 2187.
3	G. RASUVAJEV,Ber., 1931, 64, 2860.

PHENARSAZINE CHLORIDE: PROPERTIES 325

solution,1 for instance, converts phenarsazine chloride to phenarsazinic acid :

/C6H44\ / OH

HN( >As(

XCH \

e

This forms acicular crystals melting above 300° C.

However, nitric acid under certain conditions does not affect the arsenic atom, but introduces one or two nitrogroups. These groups enter at the orthoor paraposition to the NH— group.2 These nitrocompounds have vigorous irritating properties according to Libermann.3

Sodium Cyanide. Phenarsazine chloride, when treated with sodium cyanide in methyl alcohol solution, does not form phenarsazine cyanide, but the corresponding methoxycompound,

/C6HA

HN( )As-OCH3 XCeH/

This substance melts at 194° C., and on heating with water is converted to phenarsazine oxide.

Phenarsazine cyanide has, however, been prepared by Gryskiewicz4 by treating phenarsazine chloride with, silver cyanide. It forms bright yellow crystals which melt at 227° C. with decomposition according to Gryskiewiczor at 223° to 224° C. according to Gibson.6 Though it has a more efficient biological action than diphenyl cyanoarsine, it is very unstable to heating and to explosion.6

Potassium Thiocyanate. When phenarsazine chloride is treated in acetone solution with an aqueous solution of potassium thiocyanate, phenarsazine thiocyanate is formed 7 :

/C.HA

NH( >AsSCN XC6H/

This forms yellow crystals which melt at 229° to 230° C. Chloramine-T. On treatment of phenarsazine chloride in cold

aqueous alcoholic solution with chloramine-T,8 phenarsazinic acid is formed (see above).

1 WIELAND and RHEINHEIMER, Ann., 1921, 423, 7.

2	WIELAND and RHEINHEIMER, loc. cit.
3	G. LIBERMANN, Khimia i Tecnologia Otravliajuscix Vescestv, Moscow, 1931,

286.

*	GRYSKIEWICZ, Bull. soc. Mm., 1927, 41,	1323.
6	GIBSON and coll., Rec. trav. Chim., 193°,	49, 1006.

« U. MULLER, Militar-Wochenblatt., 1931, 21, 757-

7SERGEEV and coll., /. Obscei Khim., Ser. A, 1931, 1, 263.

8BURTON and GIBSON, /. Ghent. Soc., 1924, 125, 2275.