Sartori The War Gases Chemistry and analysis

DIPHENYL CHLOROARSINE: MANUFACTURE 305

After about 15 minutes the other half of the arsenic trichloride, chlorobenzene and xylene mixture is added.

When all the sodium has been introduced, the agitation is continued until the temperature of the liquid tends to drop. At 60° C. it is filtered through a press, the filtrate being collected in a still where it is heated to 220° C. in order to remove the solvent and unreacted chlorobenzene. A liquid remains which on cooling solidifies to a bright yellow, crystalline solid consisting of triphenyl arsine.

By this method large quantities of triphenyl arsine may be prepared in a relatively pure condition and in a short time. But on the other hand it is somewhat inconvenient to have to work with molten sodium, which tends to solidify in the funnel through which it is introduced.

These inconveniences may be eliminated to a great extent by using Pope and Turner's modifications. The apparatus employed by these workers consists of a vessel fitted with a reflux condenser. The sodium, freed from grease, is placed in the same vessel to which is then added the arsenic trichloride and the chlorobenzene. Benzene is employed as the solvent instead of xylene ; as this boils at 80°C. it maintains the temperature constant at the most favourable point for the reaction.

By this method the reaction takes longer than by Morgan's method, but, on the other hand, it is easier to operate and gives a better yield of triphenyl arsine.

(b) Conversion of Triphenyl Arsine into Diphenyl Chloroarsine.

c)(C6H5)3As + C6H5AsCl2 = 2 (C6H5)8AsCl

which arrive at a stage of equilibrium. Morgan and Vining studied the reaction in order to find the optimum conditions for obtaining the highest yield of diphenyl chloroarsine. They proposed heating the mixture of triphenyl arsine and arsenic trichloride in a rotating autoclave at 250° to 280° C., with an internal pressure rising to 4-2-7 kgm. per sq. cm. (60-100 Ib. per sq. in.). After 2 hours the heating is stopped and the product

3o8 ARSENIC COMPOUNDS

the calculated quantity of sodium nitrite. When the diazobenzene hydrochloride has been prepared, a solution of sodium arsenite is slowly run in. This latter is prepared beforehand by dissolving arsenious oxide in an aqueous sodium hydroxide solution which contains sufficient alkali to neutralise all the acid in the diazo solution and sufficient arsenious oxide to be 20% in excess of the theoretical quantity. 20 kgm. copper sulphate are also added to the diazotisation to accelerate the reaction.

The mixture is stirred continuously and maintained for 3 hours at 15° C., when sodium phenyl arsenate is formed. This is neutralised with hydrochloric acid and filtered through a press in order to separate resinous substances which are formed. The phenyl arsenic acid in the filtrate is reduced to phenyl arsenious oxide by passing a current of sulphur dioxide through. A heavy oil deposits at the bottom of the vessel and this is removed by decantation and redissolved in 40° Be. sodium hydroxide solution. After diluting with 8 cu. m. of water, the solution is cooled to 15° C. and run slowly into another solution of diazobenzene chloride prepared as before. The sodium salt of diphenyl arsenic acid which is formed is slightly acidified with hydrochloric acid, the diphenyl arsenic acid filtered off and redissolved in 20° Be. hydrochloric acid (i part of the arsenic acid requires 3 parts of hydrochloric acid) and the solution obtained is then run into an iron vessel, lined internally with tiles. Sulphur dioxide is then passed through for 8 hours while the temperature is maintained at about 80° C. Diphenyl chloroarsine then separates as an oil which forms a layer at the bottom of the vessel. It is separated off and dried in vacua.

PHYSICAL PROPERTIES

Crude diphenyl chloroarsine is a dark brown liquid which gradually turns into a semi-solid viscous mass.

In the pure state diphenyl chloroarsine forms colourless crystals which melt at 41° C. According to some authors it exists in two crystalline modifications, the stable one melting at 38-7° to 38-9° C.and the labile at 18-2° to 18-4° C.1 The labilemodification is easily converted into the stable form.2

1 Somewhat differing values are reported in the literature for the melting point of diphenyl chloroarsine :

37° to 38° (LEWIS and coll., /. Am. Chem. Soc., 1921, 43, 891). 38° to 39° (STEINKOPF and coll., Ber., 1928, 61, 678).

38-5° to 39° (FROMM and coll., Rec. trav. Chim., 1930, 49,623).

40° to 41° (GRYSZKIEWICZand coll., Bull. soc. chim., 1927, 41, 570). 40° to 42° (BLICKE and coll., /. Am. Chem. Soc., 1933, 55, 1161).

44° (WALTON and coll., /. Pharmacol., 1929, 35, 241). * GIBSON and VINING, /. Chem. Soc., 1924, 125, 909.

310 ARSENIC COMPOUNDS

CHEMICAL PROPERTIES

Water. Water hydrolyses diphenyl chloroarsine, forming diphenyl arsenious oxide (m.p. 92-5° to 93-5° C.) :

2(C6H5)2AsCl + H20 = [(C6H5)2As]20 + aHd.

According to several authors l this reaction is slow at normal conditions of humidity, but is considerably accelerated when the arsine is brought into contact with aqueous or alcoholic solutions of the alkali hydroxides.2

This hydrolysis is accelerated by the presence of olive oil or turpentine. In the latter case, some oxidation to diphenyl arsenic acid takes place (see p. 311).

Ammonia. With anhydrous ammonia and diphenyl chloroarsine in benzene solution, the following reaction takes place 3 :

(C6H8)2AsCl + 2NH3 = (C6H5)2AsNH2 + NH4C1.

Diphenyl arsenamide forms needles melting at 53° C. It acts on the skin and on the mucous membranes both in solution and when dispersed in the air. On exposure to air, it is converted into diphenyl arsenious oxide (see above).

Chlorine. By the action of a solution of chlorine in carbon tetrachloride on a solution of diphenyl chloroarsine in chloroform, diphenyl trichloroarsine4 is formed, as crystals melting at

189° C. :

/Cl

(C6H6)2As(-Cl

This trichloroderivative on treatment with cold water forms first the chloride of diphenyl arsenic acid :

(C6H6)2AsCl3 + 2H20 = (C6H5)2As(OH)2Cl + 2HC1,

which is rapidly converted into diphenyl arsenic acid.5 According to Meyer, diphenyl trichloroarsine has no toxic power. Chlorine water also oxidises diphenyl chloroarsine to diphenyl arsenic acid.6

Bromine. Bromine, in chloroform solution, reacts with diphenyl chloroarsine also dissolved in chloroform, forming different products according to the amount of bromine : either diphenyl chloroarsine bromide, (C6H5)2AsCl.Br2, yellow needles melting

1 LlBERMANN, loC. dt.

RONA, Z. ges. expt. Med., 1921, 13, 16. IPATIBV and coll., Ber., 1929, 62, 598.

LA COSTE and MICHAELIS, Ann., 1880, 201, 222. KAPPELMEYER, Rec. trav. Chim., 1930, 49, 79. MICHAELIS, Ann., 1902, 321, 141.

benzene1; or diphenyl chloroarsine perbromide, (C6H5)2AsCl. Br4, orange-red prisms melting at 146° to 150° C. These halogenated derivatives lose the atoms of bromine which they contain on exposure to moist air.

Nitric Acid. Diphenyl chloroarsine on heating to about 40°C. with concentrated nitric acid is oxidised to diphenyl arsenic acid, (C6H5)2AsOOH. This forms colourless crystals melting at 175° C. which are sparingly soluble in hot water, alkalies and alcohol. It is not decomposed by nitric acid, nor by boiling chromic acid. The copper and lead salts of diphenyl arsenic acid are very sparingly soluble in water, even at 100° C. Diphenyl arsenic acid dissolves in nitric acid, forming a nitrate of the formula :

(C6H5)2AsOOH.HNO3.

Hydrochloric Acid. On boiling diphenyl chloroarsine with hydrochloric acid, arsenic trichloride and triphenyl arsine are formed,2 as follows:

3(C.H5)iAsd = AsCl3 + 2As(C6H5)3. Chlorosulphonic Acid. Diphenyl chloroarsine, on treatment

with chlorosulphonic acid forms, besides benzene sulphonyl chloride, a chloride of diphenyl arsenic acid having the formula8 (C6HB)2AsOOH. HC1, which forms prisms and melts at 130° C.

Fluorosulphonic Acid. This converts diphenyl chloroarsine into benzene sulphonyl fluoride and the sulphate of diphenyl arsenic acid, 2(C6H5)2AsOOH.H2S04, melting at 117° C.

Sodium Iodide. By the action of sodium iodide on diphenyl chloroarsine dissolved in acetone, diphenyl iodoarsine4 is

obtained :

(C6H5)2AsCl + Nal = (C6H5)2AsI + NaCl.

This forms brilliant yellow crystals with m.p. 40-5° C. (or,according to Blicke,5 41° to 42° C.), insoluble in water, difficultly soluble in cold alcohol, but readily soluble in hot alcohol, ether, acetone, benzene, etc.

Hydrogen Sulphide. On bubbling sulphuretted hydrogen through an alcoholic solution of diphenyl chloroarsine, diphenyl arsenious sulphide 6 is formed :

3i2 ARSENIC COMPOUNDS

This forms white acicular crystals at 67° C. It is readily soluble in benzene, carbon disulphide and chloroform, but sparingly in alcohol and ether. This sulphide may also be obtained by the action of sodium sulphide on diphenyl chloroarsine in benzene solution * ; on treatment with mercuric cyanide or silver cyanide, diphenyl cyanoarsine is obtained (see p. 314).

Sodium Thiocyanate. By the action of sodium thiocyanate dissolved in acetone on diphenyl chloroarsine dissolved in the same solvent, diphenyl thiocyanatoarsine is formed,2 (C6H5)2AsSCN, an oily, pale brown substance, which is miscible in all proportions with benzene and acetone and which decomposes with water, giving up the SCNgroup. It boils at 230° to 233° C. at 22-23 mm. mercury pressure. It reacts quantitatively with sodium sulphide3:

2(C6H6)2AsSCN + NaaS = [(C6H6)2As]aS + 2NaSCN.

Sodium Alcoholate or Phenate. Sodium alcoholate and phenate react with diphenyl chloroarsine as follows 4 :

(C,H,)iAsa + C2H6ONa = (C6H6)2AsO.C2H6 + NaCl (C6H5)2AsCl + C8H5ONa = (C6H5)2AsO.C6HB + NaCl

Methyl Iodide. On heating diphenyl chloroarsine with methyl iodide to 100° C. in a closed tube, a mixture of diphenyl iodoarsine (see p. 311) and dimethyl diphenyl arsonium triiodide,5 (CH3)2(C6H5)2AsI3, is obtained.

Acyl Chlorides. When diphenyl chloroarsine is treated with one of the aliphatic acyl chlorides, like acetyl chloride, dissolved in carbon disulphide and in presence of aluminium chloride, acetophenone and arsenic trichloride are formed 6 :

(C6H5)2AsCl + 2CH3COC1 = 2C6H5COCH3 + AsCl3.

Phenyl Arsines. When diphenyl chloroarsine is treated with (mono)phenyl arsine in an atmosphere of nitrogen or carbon dioxide,7 arsenobenzene and tetraphenyl diarsine are formed 8 :

4 (C6H5)2AsCl + 2 C6H5AsH2 ->

C6H5As=AsC6H5 + 2 (C6Hs)2As-As(C6H5)2 + 4 HC1

MORGAN and VINING, /. Ghent. Soc., 1920, 117, 777.

STEINKOPF and W. MIEG, Ber., 1920, 53, 1013.

PANCENKO and coll., /. Obscei Khim., Ser. A, 1932, 2, 193.

MICHAELIS, Ann., 1902, 321, 143.

STEINKOPF and SCHWEN, Ber., 1921, 54, 1458.

MALINOVSKY, /. Obscei Khim., Ser. A, 1935, 5. 1355.

STEINKOPF and DUDEK, Ber., 1929, 62, 2494.

BLICKE and coll., /. Am. Chem. Soc., 1932, 54, 3353.

3i4 ARSENIC COMPOUNDS

C6H5\

)AsBr

C.H./

This substance was prepared in 1880 by La Coste and Michaelis,1 but was tested as a war gas only in the post-war period.

PREPARATION

According to Steinkopf2 it may be obtained in the laboratory by heating 35 gm. diphenyl arsenious oxide with more than I gramme-molecule of hydrobromic acid to 115° to 120° C. for

4hours.

Industrially, diphenyl bromoarsine is prepared by methods

similar to those described above for the preparation of the chloro-compound. That is to say, by the action of arsenic tribromide on triphenyl arsine at 300° to 350° C. or else by the diazotisation method, using hydrobromic acid instead of hydrochloric acid.

PHYSICAL AND CHEMICAL PROPERTIES

Diphenyl bromoarsine forms white crystals and melts at 54° to 56° C. Its chemical properties are similar to those of diphenyl chloroarsine.

Treated with a solution of chlorine in carbon tetrachloride, yellow crystals separate on cooling and these consist of bromo dichloro diphenyl arsine, (CgH^AsClgBr, and melt at 109° to

116° C.s

By the action of bromine on diphenyl bromoarsine in chloroform, diphenyl tribromoarsine is formed. This has the formula (C6H5)2AsBr3, and forms yellow crystals which melt at 126° C. Excess of bromine forms the perbromide, (C6H5)2AsBr6, orange-red crystals which begin to melt at 115° C.3

Diphenyl bromoarsine has similar physiopathological properties to the corresponding chloro-compound, but a milder aggressive action.

Diphenyl cyanoarsine was first prepared by Sturniolo and Bellinzoni.4

1 LACOSTE and MICHAELIS, Ann., 1880, 201, 230.

2STEINKOPF and SCHWEN, Her., 1921, 54, 1458.

3KAPPELMEYER, Rec. trav. Chim., 1930, 49, 77.

4 STURNIOLO and BELLINZONI, Boll. Chim. Farm., 1919, 58, 409.

DIPHENYL CYANOARSINE: PREPARATION 315

It was employed as a war gas towards the end of the war (May, 1918) both alone and mixed with diphenyl chloroarsine.

PREPARATION

This substance wasmade during the war 1 by heating potassium cyanide with diphenyl chloroarsine :

(C8H5)2AsCl + KCN = (C6H5)2AsCN + KC1.

However, it was later 2 discovered that this method of preparing diphenyl cyanoarsine had the disadvantage that the product is sensitive to alkaline reagents such as sodium or potassium cyanide.

In the other methods worked out since the war, diphenyl cyanoarsine is prepared by treating diphenyl arsenious oxide with hydrocyanic acid, or by treating either diphenyl chloroarsine or diphenyl arsenious sulphide with the cyanide of a heavy metal. The reaction between hydrocyanic acid and diphenyl arsenious oxide may be carried out at the ordinary temperature3 or by treatment in a closed tube at 100° C. for 2 hours 4 :

[(C.HJ.Asl.O + 2HCN = 2(C6H5)2AsCN + H2O.

The reaction with the heavy metal cyanides may be brought about either by treating diphenyl chloroarsine at 150° to 160° C. for 3 hours with dry, recently prepared silver cyanide, or by the treatment of diphenyl arsenious sulphide with mercuric cyanide for 2 hours at 160° to 200° C.5

LABORATORY PREPARATION

The preparation of diphenyl cyanoarsine in the laboratory may be carried out by the action of potassium cyanide on diphenyl chloroarsine.

4-5 gm. potassium cyanide are dissolved in 20-25 ml. water in a 100 ml. flask and 15 gm. diphenyl chloroarsine are added in small portions with continuous stirring. The reaction is exothermic and the flask should be cooled externally with water so as to maintain the internal temperature at 40° to 45° C. When the temperature commences to fall, the product is allowed to stand. An oil separates at the bottom of the flask and is washed with water and allowed to crystallise by cooling. The product obtained is