Synthesis of 3-Methyl-4-nitrobenzoic Acid via Catalytic Oxidation with Molecular Oxygen

3-Methyl-4-nitrobenzoic acid was synthesized via oxidation of 2,4-(dimethylnitrobenzene) with mole-(cular) oxygen catalyzed by cobalt acetate in acetic acid in the presence of an initiator.It was found that the yield of 3-methyl-4-nitrobenzoic acid increased remarkably with the addition of sodium bromide as a co-(catalyst).The reaction was carried out at 130 ℃ for 8 h at 0.8 MPa of oxygen in the presence of 0.017 mol of cobalt acetate,(0.017 mol) of sodium bromide,and 0.30 mol of 2-butanone with 1.00 mole of 2,4-dimethylnitrobenzene.(Under) these conditions 99% of the reactant converted with a selectivity of 52% to 3-methyl-4-(nitrobenzoic) acid,and the yield of 3methyl-4-(nitrobenzoic) acid was 51%.The reaction mechanism and the function of(sodium) bromide were discussed.According to the fact that the reaction could not proceed without the presence of an initiator,it was proposed that the reaction took place via a free radical mechanism,and(sodium) bromide reacted with Co(Ⅲ) to generate bromine radicals,which promoted the formation of benzyl radicals.