The oxidation of the various aliphatic, aromatic and heteroaromatic thioethers was carried out in a range of ionic liquids, 1-butyl-3-methylimidazolium triflate, 1-butyl-1-methyl-pyrolidinium bis(trifluoromethanesulfonyl)amide, 1-butyl-3-methyl-imidazolium bis(trifluoromethanesulfonyl)amide, 1-butyl-3-methyl-imidazolium tetrafluoborate and 1-butyl-2,3-dimethylimidazolium bis(trifluoromethane-sulfonyl)amide, using sol-gel prepared mixed oxide silica tantalum and tantalum grafted MCM-41 catalysts. For comparison catalytic tests in molecular solvents (acetone, acetonitrile, dioxane and ethanol) were also performed. Excellent hydrogen peroxide efficiencies were obtained on these catalysts. The conversion data has been correlated with the Kamlet-Taft pi*, alpha and beta solvent parameters. Characterization of the catalysts was made by ICP-AES, adsorption-desorption isotherms of N-2 at 77 K, XRD, SEM and TEM. (C) 2006 Elsevier B.V. All rights reserved.