The epoxidation of cyclohexene catalyzed by Keggin-type heteropoly compounds (HPAs) were investigated using anhydrous urea-hydrogen peroxide adduct (UHP) as an oxidant and acetonitrile as a solvent. Among a series of Keggin-type heteropoly compounds, tris(cetylpyridinium) 12-tungstopbosphate (CWP) showed the highest activity. By optimizing the reaction conditions, 80% conversion of cyclohexene and 97% selectivity for cyclobexene oxide could be achieved in the UHP/CH3CN system. When aqueous 30% hydrogen peroxide (H2O2, HP) was used, the cyclohexene conversion and cyclohexene epoxide selectivity were inferior to those obtained with the UHP/CH3CN system. The reaction of UHP with CWP has been studied by UV-Vis and P-31 NMR spectroscopy, which has revealed that the Keggin-type heteropoly compounds CWP is degraded in the presence of excess UHP to form a considerable amount of phosphorus-containing species. (C) 2004 Elsevier B.V. All rights reserved.