Reactions of lead(IV). Part XXVIII. Oxidative coupling of methylsubstituted benzenoid compounds: formation of biaryls and diarylmethanes in trifluoroacetic acid

Abstract

Methyl-substituted benzenes are oxidised readily at low temperatures by lead tetra-acetate in the presence of trifluoroacetic acid; the products are mainly biaryls and diarylmethanes, in proportions which vary markedly with the structure of the aromatic compound. Evidence has been adduced that the first step is the formation of an aromatic radical cation. This undergoes competitive reactions; it can react with another aromatic molecule to give ultimately a biaryl, and in this respect behaves as an electrophilic radical rather than as a cation, or it can undergo further oxidation to give a benzylic cation from which diarylmethanes are derived.