Phenylation, Benzoyloxylation and Halogenation of Aromatic Compounds by Silver Benzoate – Halogen Complexes

Abstract

ALTHOUGH the reaction between halogens and the silver salts of carboxylic acids constitutes a fairly well-known method for the preparation of organic halides, its mechanism is far from clear. Several types of intermediate have been isolated or postulated by different workers^1,2. Simonini³ obtained complexes which he formulated as (RCO₂)₂AgX (where X = halogen), for example, the so-called ‘silver iodide dibenzoate’. Birckenbach and Meisenheimer⁴ examined the decomposition of certain of these complexes in the presence of benzene, using a reaction between one equivalent of the silver salt and two equivalents of iodine. The formation of iodobenzene and the phenyl ester of the acid was reported. From a reaction between silver p-chlorobenzoate and iodine in boiling chlorobenzene, p-chlorophenyl p-chlorobenzoate was isolated. In this latter case, it is not clear from the experimental evidence whether the ester resulted from a reaction with the solvent, or whether both its P-chlorophenyl groups originated in the silver salt. It is known that esters, RCO₂ R, can result from analogous reactions between silver salts, RCO₂Ag, and iodine⁵. A preliminary investigation of this subject has exposed several interesting new features, which are now briefly described.