When pure, diphenylchloroarsine is a colorless solid, melting at 44°. Because of this, it was always used in solution in a toxic gas or in a shell which contained a large amount of explosive so that on the opening of the shell the material would be finely divided and scattered over a wide territory.
Its value lay in the fact that the fine particles readily penetrated the ordinary mask and caused the irritation of the nose and throat, which resulted in sneezing. This necessitated the perfection of special smoke filters to remove the particles, after which the other toxic materials were removed by the absorbent in the canister.
It causes sneezing and severe burning sensations in the nose, throat and lungs in concentrations as slight as 1 part in 10 million. In higher concentrations, say 1 in 200 to 500 thousand it causes severe vomiting. While neither of these effects are dangerous or very lasting, still higher concentrations are serious, as in equal concentrations diphenylchloroarsine is more poisonous than phosgene.
Various other arsenical chemicals were developed in the laboratory, but with one or two exceptions they were not as valuable as diphenylchloroarsine and methyldichloroarsine and were therefore discarded.
German Methods for Manufacturing
Arsenicals[23]
Diphenylchloroarsine
“This substance (Blue Cross) was a famous gas of the Germans and was made in large quantities. The method used by the Germans was different from the one worked out by the Allies, and on account of the fact that the German method could be carried out without specially designed apparatus and required as raw materials substances readily obtainable, it was probably preferable. It is doubtful, however, whether the Allies would have made this gas, for as the result of its use no fatalities were reported. The German process consisted in preparing phenylarsenic acid by condensing benzene diazonium chloride with sodium arsenite. The acid was next reduced by sulfur dioxide to phenylarsenous acid, which was, in turn, condensed with the diazonium compound to form diphenylarsenic acid. This acid was reduced to diphenylarsenous oxide, which with hydrochloric acid yielded diphenylchloroarsine. The chemical equations for the reactions will make clearer the steps involved.
| C₆H₅N₂Cl + Na₃AsO₃ | = | C₆H₅AsO₃Na₂ + NaCl + N₂ |
| C₆H₅AsO₃Na₂ + 2HCl | = | C₆H₅AsO₃H₂ + 2NaCl |
| C₆H₅AsO₃H₂ + SO₂+H₂O | = | C₆H₅AsO₂H₂ + H₂SO₄ |
| C₆H₅N₂Cl + C₆H₅AsO₂Na₂ | = | (C₆H₅)₂AsO₂Na + NaCl + N₂ |
| (C₆H₅)₂AsO₂Na + HCl | = | (C₆H₅)₂AsO₂H + NaCl |
| 2(C₆H₅)₂AsO₂H + 2SO₂ + H₂O | = | [(C₆H₅)₂As]₂O + 2H₂SO₄ |
| [(C₆H₅)₂As]₂O + 2HCl | = | 2(C₆H₅)₂AsCl + H₂O. |
“The entire process was carried out at Höchst. The method used at Höchst was as follows: In preparing the diazonium solution, 3 kg.-mols of aniline were dissolved in 3000 liters of water and the theoretical quantity of hydrochloric acid. The temperature of the solution was reduced to between 0° and 5° and the theoretical amount of sodium nitrite added. The reaction was carried out in a wooden tank of the usual form for the preparation of diazonium compounds. A solution of sodium arsenite was prepared which contained 20 per cent excess of oxide over that required to react with the aniline used. The arsenous oxide was dissolved in sodium carbonate, care being taken to have enough of the alkali present to neutralize all of the acid present in the solution of the diazonium salt. To the solution of the sodium arsenite were added 20 kg. of copper sulfate dissolved in water, this being the amount required when 3 kg.-mols of aniline are used. The solution of the diazonium compound was allowed to flow slowly into the solution of the arsenite while the temperature was maintained at 15°. The mixture was constantly stirred during the addition which requires about 3 hrs. After the reaction was complete, the material was passed through a filter press in order to remove the coupling agent and the tar which had been formed. Hydrochloric acid was next added to the clear solution to precipitate phenylarsenic acid, the last portions of which were removed by the addition of salt.
“The phenylarsenic acid was next reduced to phenylarsenous acid by means of a solution of sodium bisulfite, about 20 per cent excess of the latter over the theoretical amount being used. For 100 parts of arsenic acid, 400 parts of solution were used. The reaction was carried out in a wooden vessel and the mixture stirred during the entire operation. A temperature of 80° was maintained by means of a steam coil. Phenylarsenous acid separated as an oil. The aqueous solution was decanted from the oil, which was dissolved in a solution of sodium hydroxide, 40° Bé. The solution of the sodium salt of phenylarsenous acid was treated with water so that the resulting solution had a volume of 6 cu. m. when 3 kg.-mols of the salt were present. Ice was next added to reduce the temperature to 15° and a solution of benzene diazonium chloride, prepared in the manner described for the first operation, was slowly added. After the coupling, diphenylarsenic acid was precipitated by means of hydrochloric acid. The acid was removed by means of a filter press and dissolved in hydrochloric acid, 20° Bé. For one part of diphenylarsenic acid, 3 parts of hydrochloric acid were used. Into this solution was passed 5 per cent excess of sulfur dioxide over that required for the reduction. The sulfur dioxide used was obtained from cylinders which contained it in liquid condition.