Selective Oxidation of p-Chlorotoluene Catalyzed by Co/Mn/Br in Acetic Acid-Water Medium

Liquid-phase selective oxidation of p-chlorotoluene catalyzed by Co/Mn/Br with molecular oxygen under atmospheric pressure was studied. Acetic acid-water was used as the reaction medium in place of the commonly used pure acetic acid, which inhibited the further oxidation of p-chlorobenzaldehyde and enhanced the selectivity. Moreover, it is advantageous to use acetic acid-water as the reaction medium because water is a product of the reaction and the separation of the acetic acid-water mixture thus formed is a difficult and uneconomic process. The effects of the initial water concentration, Co/Mn and Br/(Co+Mn) mole ratios, amount of the catalyst, pchlorotoluene/solvent volume ratio, reaction temperature, reaction time, and oxygen flow rate were investigated. The optimum reaction conditions were as follows: initial water concentration of the solvent 10 wt %, Co/Mn mole ratio 0.67, Br/(Co+Mn) mole ratio 0.4, amount of the catalyst accounting for 4 wt % of the substrate, p-chlorotoluene/solvent volume ratio 1.5, reaction temperature 106 °C, reaction time 10 h, and the oxygen flow rate 10 mL/min. Under these conditions, a 14.3% yield of p-chlorobenzaldehyde was obtained at 19.7% conversion of p-chlorotoluene with 72.4% selectivity.