Epoxidation of alkenes with hydrogen peroxide catalyzed by ReO4–SiO2·Al2O3 and ReO4–Al2O3

Rhenium oxides supported on zeolite Y, mixed silica–alumina and pure alumina were prepared by impregnation of the supports with Re 2 O 7 or NH 4 ReO 4 . The materials are active catalysts in the epoxidation of cyclooctene and cyclohexene with anhydrous H 2 O 2 in EtOAc. Catalyst stabilities with regard to metal leaching are closely correlated with the alumina content of the support and almost no leaching was observed with ReO 4 − supported on pure alumina. Stable catalysts ReO 4 –Al 2 O 3 with ReO 4 − contents up to 12 wt.% can be prepared. Higher contents result in extensive metal leaching and catalysis in the homogeneous phase. The catalyst ReO 4 (12 wt.%)–Al 2 O 3 was re-used in three catalytic runs, without loss of activity. Selectivities for cyclooctene epoxide were around 96%, whereas cyclohexanediol was obtained as the only product in cyclohexene epoxidation. Adding pyridine to the reaction mixtures, the selectivity for cyclohexene epoxide increased from 0 to 67%, however, a significant decrease in conversion was observed.