Selective oxidation of p-chlorotoluene with Co(OAc)2/MnSO4/KBr in acetic acid–water medium

Selective oxidation of p-chlorotoluene catalyzed by Co(OAc)2/MnSO4/KBr with molecular oxygen has been studied. Acetic acid–water is used as the reaction medium in place of pure acetic acid to avoid the nuisance of acetic acid separation. It is found that when MnSO4 is used in place of the commonly used Mn(OAc)2, MnO2 barely forms and the activity of the composite catalyst greatly enhances. Under the optimized conditions (Co/(Co + Mn) mole ratio 0.2, Br/(Co + Mn) mole ratio 0.3, and reaction temperature 106 °C), 22.4% yield of p-chlorobenzaldehyde was obtained at 33.7% conversion of p-chlorotoluene with 66.6% selectivity.