Catalytic oxidation of thioanisole Ph–S–CH3 over VOx/SiO2 and VOx/Al2O3 catalysts prepared by sol–gel method

Abstract

The catalytic oxidation of thioanisole to the sulfoxide and sulfone using TBHP or H2O2 as oxidants in CH2Cl2 or MeOH as solvents was carried out over VOx/SiO2 or VOx/Al2O3 catalysts prepared by a sol–gel method. It was found that the catalytic activity and selectivity of the reaction depended on the nature of the support (SiO2 or Al2O3), the drying mode (xerogel or aerogel), the calcination of the solid and the vanadium-peroxide species formed. The TBHP/CH2Cl2 system gave a very high activity and selectivity, mainly in the cases of vanadia-silica xerogels, with total thioanisole conversion and a sulfoxide/sulfone ratio of 97/3. This activity was truly heterogeneous but vanadium leaching was observed with vanadia-silica aerogels. In contrast, vanadia-alumina catalysts were less active and less selective. The use of the H2O2/MeOH system led to vanadium leaching with all types of catalysts.