Oxidation of coals in liquid phases. X. Mechanism of the cleavage of benzenecarboxylic acids to oxalic acid and carbon dioxide by the base-catalyzed oxygen-oxidation

Article abstract of DOI:10.1246/bcsj.63.159

A kinetic study of the oxidation of benzenecarboxylic acids has been performed in order to clarify the mechanism. The reaction products were oxalic acid and carbon dioxide, along with a trace of acetic acid. The oxidation rate of phthalic acid was proportional to the first order of the molality of phthalic acid, the molality of NaOH, and partial oxygen pressure, respectively; the apparent activation energy was 126 kJ mol^-1. These results show that the rate-determining step is a cleavage of the benzene ring proceeded by a base-catalyzed oxygen-oxidation mechanism in which a carbanion formed by hydrogen extraction from an aromatic ring is attacked by oxygen. In the cleavage of phthalic acid, NaOH increases the selectivity to form oxalic acid as well as the oxidation rate. In the oxidation of 1,2,3-benzentricarboxylic acid the same mechanism was recognized, but not for benzenehexacarboxylic acid which has no hydrogen on the benzene ring.