Peroxotungstates immobilized on multilayer ionic liquid brushes-modified silica as an efficient and reusable catalyst for selective oxidation of sulfides with H2O2

Article abstract of DOI:10.1016/j.molcata.2011.03.024

Peroxotungstates held in a series of different supported ionic liquid brush catalysts were synthesized and characterized. Their catalytic performance towards the selective oxidation of sulfides with aqueous hydrogen peroxide was investigated under mild conditions. We found that the catalytic activities of the different catalysts depend on the number of supported ionic liquid layers and N-end-capped alkyl group on the imidazole ring. The highest yield of methyl phenyl sulfoxide was obtained using the BisILs-C₈H₁₇-W2 catalyst under optimum conditions. The sulfides were selectively oxidized to sulfoxides in high yields with trace sulfones detected by GC upon using 1.1 equivalents of H₂O₂. At 2.5 equivalents of H ₂O₂ the sulfones were found to be the main products. It is noteworthy that the catalyst resulted in high chemoselectivity towards sulfur groups with unsaturated double bonds even though excess hydrogen peroxide was used in addition to exhibiting high catalytic activity. There was no apparent loss of catalytic efficiency until the 8th cycle.