Highly selective electrochemical oxidation of 2-nitro-4-methylsulfonyltoluene to 2-nitro-4-methylsulfonylbenzoic acid enabled by molybdate

It is urgent to develop a green synthesis approach for 2-nitro-4-methylsulfonylbenzoic acid (NMSBA) production as nitric acid oxidation procedure generates large amount of waste acid and nitrogen oxide. Herein, highly selective electrochemical oxidation of 2-nitro-4-methylsulfonyltoluene (NMST) was achieved under ambient pressure and temperature by employing molybdate as the catalyst and graphite rod as the anode. Through optimizing the catalyst dosage, phase transfer catalyst dosage, reactant concentration, electrolyte concentration, cell voltage and reaction time, the NMSBA selectivity of 95.16% was realized in acidic media with the NMST conversion of 57.37%. DFT calculations demonstrate that molybdate in the form of Mo 2 O 7 2− can catalyze the oxidation of NMST in acidic media. NMST loses hydrogen from the methyl group, subsequently accepts oxygen, and finally converts into NMSBA. This work not only demonstrates molybdate as an efficient catalyst for the first time, but also provides a new electrochemical approach for highly selective production of NMSBA. Graphical Abstract