text: It was first produced in 1878 by the German chemists August Michaelis (1847–1916) and Wilhelm La Coste (1854–1885). It is prepared by the reduction of diphenylarsinic acid with sulfur dioxide. An idealized equation is shown:
  :PhAsOH + SO + HCl → PhAsCl + HSO
  The process adopted by Edgewood Arsenal, the "sodium process", for the production of DA for chemical warfare purposes employed a reaction between chlorobenzene and arsenic trichloride in the presence of sodium.
  The German process, used in the first war, applied at Hochstam-Main, used the Sandmeyer reaction between phenyldiazonium chloride and sodium arsenite. The acidified product was reduced and then neutralized. The salt was condensed again by the Sandmeyer reaction and reduced again, the final product was then acidified, resulting in DA.
  The structure consists of pyramidal As centre. The As-Cl distance is 2.26 A and the Cl-As-C and C-As-C angles are 96 and 105°, respectively.