A divanadium-substituted phosphotungstate [ホウ-PW10O38V2(ホシ-OH)2]3- (I) could act as an efficient homogeneous catalyst for selective oxidn. of sulfides with 30% aq. H2O2. By using I at 0.01-0.1 mol%, various kinds of sulfides including aryl, alkyl, and vinyl ones could be converted into the corresponding sulfoxides in excellent yields with one equiv. of H2O2 with respect to sulfides. The neg. Hammett マ�value (-0.83) for competitive oxidn. of p-substituted thioanisoles and the low XSO (XSO = (nucleophilic oxidn.)/(total oxidn.)) value (<0.01) for the I-catalyzed oxidn. of thianthrene 5-oxide (SSO) revealed that I produces a strong electrophilic oxidant. [on SciFinder(R)]