Abstract：A new process for the preparation of p-toluic acid by selective p-xylene liquid phase catalytic oxidation of p-xylene was studied at 135 ℃ with oxygen as oxidant, potassium or sodium salt as cocatalyst. On the basis of screening suitable cobalt salt catalysts, the effects of catalyst concentration, oxygen flow rate and reaction time on the p-xylene conversion and the oxidation product selectivity were investigated and the optimized reaction conditions were obtained. The results showed that when the molar ratio of p-xylene and cobalt naphthenate was 1 000:1, the O2 flow rate was 100 mL /min and the reaction time was 5 h at 135 ℃, the p-xylene conversion was 30.5% with the selectivity of 58.4% for p-toluic acid. The addition of a potassium or sodium 4-methylbenzoate could significantly inhibit the formation of ester in the oxidation products and reduce the high boilers in the reaction system.
