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

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 H2O2 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.

Graphical abstractA highly efficient, environmentally benign and reusable immobilized ionic liquid brush catalyst has been developed for the selective oxidation of sulfides to sulfoxides and sulfones with aqueous H2O2 at room temperature. The catalyst can be reused at least eight times without noticeable loss of the catalytic activity.Figure optionsDownload full-size imageDownload high-quality image (162 K)Download as PowerPoint slideHighlights► Peroxotungstates held in different supported ionic liquid brushes catalysts were synthesized. ► The catalysts combine the advantages of ionic liquid, PTC and peroxotungstate catalyst together. ► The catalyst both exhibit high catalytic activities and provide excellent chemselectivities. ► There was no apparent loss of catalyst efficiency until the 8th cycle. ► The use of H2O2 as oxidant makes the reaction possess the advantages of green and clean.