Solvent, metal and halogen-free synthesis of sulfoxides by using a recoverable heterogeneous urea-hydrogen peroxide silica-based oxidative catalytic system

An efficient and green protocol was used for the selective oxidation of sulfides to sulfoxides by using silica sulfuric acid (SSA) as a recoverable heterogeneous solid acid catalyst in the presence of urea-hydrogen peroxide (UHP) under toxic transition metal-, solvent- and halogen-free conditions at room temperature. The present method offers several noteworthy advantages, such as high product yields, easy work-up, non-toxicity, easy preparation and reusability of the catalyst for at least six runs, which make this procedure the most convenient and attractive with low cost of catalyst and oxidant.