The reduction of p -arsanilic acid ( p -aminophenylarsonic acid) to its arsonous acid or arsine oxide: A case study

Abstract

Abstract

Zwitterionic p-arsanilic acid was not reduced by either triphenylphosphine or tris(dimethylamino)phosphine in methanol in the presence of a catalytic quantity of iodine. The hydrochloride of p-arsanilic acid was reduced by triphenylphosphine/iodine to an intermediate which, after neutralization, decomposed to a mixture of the bis-ammonium salt of p-arsanilic acid and (p-aminophenyl)arsine oxide. When the reduction was done in the presence of 1–3 mol equivalents of hydrochloric acid, then mixtures of the oxide and dichloroarsine, as their hydrochlorides, were obtained. Treatment of both products with aqueous ammonia gave the bis-ammonium salt of p-arsanilic acid and (p-aminophenyl)arsine oxide. The reactivity of all reduction products was evaluated by reaction with a variety of thiols. The As(III) and As(V) groups as substituents deshield the phenyl protons in the ¹H NMR spectra.