Oxidations of organic compounds by cobaltic salts. Part VII. The oxidation of toluene and its promotion by aliphatic acids

Abstract

The oxidation of toluene by cobaltic perchlorate in 50% aqueous methyl cyanide is a slow reaction, substantially of the first order with respect to both [Co^III] and [PhMe], which yields mainly benzaldehyde and benzoic acid together with traces of benzyl alcohol and bibenzyl. Faster oxidation of the toluene occurs in the presence of propionic, isobutyric, and pivalic acids, all of which concurrently oxidise. This induced oxidation of toluene is ascribed to the production of alkyl radicals from the carboxylic acids, i.e., R·CO₂—Co^III→ R·+ CO₂+ Co^II, R·+ CH₃·Ph → RH +·CH₂·Ph, followed by Ph·CH₂·+ Co^III+ H₂O → Ph·CH₂OH + Co^II+ H⁺, etc.

The product yields from the toluene are different for the direct and catalysed reactions and depend on the acid used. The variation of the benzaldehyde yields with changes in concentration of the various reagents has been measured.

The implication of these findings in connection with the elucidation of the detailed mechanism of metal-ion-catalysed autoxidations is noted.