Production of NMSBA from the oxidation of NMST in the homogeneous Co/Mn/Br/H₃PMo_xW_12−xO₄₀ catalytic system

Abstract

2-nitro-4-methylsulphonylbenzoic acid (NMSBA) is an important intermediate for the preparation of the highly effective herbicide mesotrione. NMSBA is produced from the oxidation of 2-nitro-4-methylsulphonyltoluene (NMST) by nitric acid commercially, which suffers from the serious problems of low yield and heavy pollution. In this paper, a homogeneous system consisting of Co/Mn/Br/ Á H 3 PMo x W 12Àx O 40 has been applied to catalyze the production of NMSBA by oxidizing NMST with oxygen in acetic acid. The experiments indicate that the best value of x in the phosphomolybdenum tungsten heteropoly acid is 3. The optimum composition of this catalyst system is 1163 ppm H 3 Pmo 3 W 9 O 40 Á 12.17H 2 O, 247.5 ppm Co, 453.5 ppm Mn, and 1075 ppm Br. Such a catalytic system is able to achieve a NMST conversion of 94.93% and a NMSBA selectivity of 99.84%. H 3 PMo 3 W 9 O 40 exceeds both H 3 PMo 12 O 40 and H 3 PW 12 O 40 as a catalyst in the production of NMSBA from the oxidation of NMST by oxygen. K E Y W O R D S 2-nitro-4-methylsulphonylbenzoic acid, 2-nitro-4-methylsulphonyltoluene, catalytic oxidation, phosphomolybdenum tungsten heteropoly acid