The tungsten and zinc oxides supported on SnO2 (W-Zn/SnO2) could act as effective and reusable solid catalysts for selective oxidn. with aq. H2O2. Various kinds of org. substrates such as olefins, amines, silanes, and sulfides could be converted into the corresponding epoxides, N-oxides, silanols, and sulfoxides in high to excellent yields. The present system was applicable to larger-scale epoxidn. of cyclooctene with one equiv. of H2O2 (20 mmol scale) with respect to cyclooctene, and the corresponding epoxide could be isolated in 88% yield. In this case, the turnover no. reached up to 650 and the turnover frequency was 108 h-1, and these values were larger than those of the heterogeneous tungsten catalysts. The obsd. catalysis for the present epoxidn. was truly heterogeneous and the recovered catalyst could be reused several times without an appreciable loss of its high catalytic performance. The kinetic, mechanistic, and spectroscopic studies show that polytungstates with dioxo groups play an important role in the present epoxidn. [on SciFinder(R)]
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