Production of NMSBA from the oxidation of NMST by air under the catalysis of sandwich-type polyoxometalate

BACKGROUND Mesotrione, a key herbicide for weed management and yield improvement in broad-leaved crops including corn, is synthesized with 2-nitro-4-methylsulfonylbenzoic acid (NMSBA) as an important intermediate. The commercial synthesis of NMSBA typically begins with the nitration of 4-methylsulfonyltoluene to form 2-nitro-4-methanesulfonyltoluene (NMST), followed by oxidation with nitric acid. However, the utilization of nitric acid gives rise to severe environmental and ecological concerns due to its corrosive nature and inherent hazards. Consequently, there is an imperative need to develop a sustainable and green oxidation process for the conversion of NMST to NMSBA in order to mitigate the reliance on chemical oxidants and their associated environmental impacts. RESULTS The synthesis of NMSBA, a catalytic system composed of Co, Mn, Br and sandwich-type polyoxometalate, has been developed to aid the oxidation of NMST to NMSBA by air. The sandwich-type polyoxometalate (POM) {K 10 Co x Mn 4− x (H 2 O) 2 P 2 W 18 O 68 } was synthesized and the best Co/Mn atomic ratio was determined to be 1.5:2.5. The doping of Ce in the POM as a counter-cationic metal improved the selectivity to NMSBA, and the best Ce/K atomic ratio was determined to be 1:7. The immobilization of {CeK 7 Co 1.5 Mn 2.5 (H 2 O) 2 P 2 W 18 O 68 } on activated carbon (AC) not only enhanced the reaction rate and the production of NMSBA but also reduced the amount of POM used. The optimal loading amount of the POM on AC was 20%. CONCLUSION Experiments revealed that the catalytic system composed of Co, Mn, Br and {K 10 Co 1.5 Mn 2.5 (H 2 O) 2 P 2 W 18 O 68 } was superior to the catalytic system consisting of Co, Mn, Br and heteropoly acids H 3 PW 12 O 40 /H 3 PMo 12 O 40 . The catalytic performance of {CeK 7 Co 1.5 Mn 2.5 (H 2 O) 2 P 2 W 18 O 68 }/AC exceeded that of H 3 PMo 3 W 9 O 40 /AC in the production of NMSBA by oxidizing NMST with oxygen. © 2025 Society of Chemical Industry (SCI).