Sulfoxidation of 2-thiomethyl-4,6-dimethyl-pyrimidine and methyl-dodecyl-sulfure was carried out in liquid phase using H2O2 in dioxane (6 or 18 wt%) and several molybdenum and mixed antimony-molybdenum oxides such as: Mo8O23, MoO3-basal, MoO3-iSO, Sb2MoO6 and a mixture of Sb2Mo10O31, and Sb4Mo10O31 (SbxMo10O31) phases as catalysts. Both catalytic performances and catalysts stability (structural modifications and leaching) depended on characteristics of the structure. The less active catalysts exhibited a higher leaching. The most stable and thus active catalysts were those for which the leaching is compensated by structural changes going in the direction of the exacerbation of their crystallinity. In the investigated series the most effective were the Mo8O23 and Sb2MoO6. (c) 2007 Elsevier B.V. All rights reserved.