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.