Oxidation of p-methoxytoluene by manganese(III) and iron(III) acetates in the presence of strong acid

Abstract

In contrast to the oxidation of various alkylbenzenes with manganese(III) acetate in acetic acid containing strong acid (e.g. HClO₄, CF₃SO₃H, or H₂SO₄), where diarylmethanes are almost the only products, a similar treatment of p-methoxytoluene afforded biaryls as the main products. In the presence of less strong acids such as CF₃CO₂H or CCl₃CO₂H, or a low concentration of HClO₄, however, diarylmethanes are mainly obtained. On the other hand, with iron(III) acetate diarylmethanes are almost the only products even in the presence of strong acid, as has been observed with other alkylbenzenes. The different behaviour between the metal acetates is explained by assuming a considerable difference in the stability of an oxygen-centred trinuclear species which works as a base to remove a proton from a radical-cation intermediate.