Oxidation of p–xylene to terephthalic acid in benzoic acid and methyl ester of p–toluic acid

Abstract

The oxidation of p-xylene to terephthalic acid has been studied at 130 to 190 °C, using benzoic acid and methyl ester of p-toluic acid as the solvent. It was found that the solvent affects strongly the activity of the cobalt catalyst which effect is dependent on the presence of bromide and pyridine ligands. In the methyl ester of p-toluic acid as the solvent, cobalt-bromide catalysts induce also hydrolysis of the methyl ester which proceeds parallelly to the oxidation of p-xylene. The activating effect of bromide and pyridine ligands results from their effect on the rate of the reaction of peroxy radicals with the catalyst in the propagation step and from their effect on the rate of consecutive oxidation of p-toluic acid to terephthalic acid.