Epoxidation of Alkenes by Hydrogen Peroxide over 12-Heteropolyacids of Molybdenum and Tungsten (H3PMo3W9O40) Combined with Cetylpyridinium Bromide

Abstract

In the epoxidation of 4-vinylcyclohex-1-ene with H2O2 in monophasic acetonitrile solution catalysed by Keggin-type 12-heteropolyacids, i.e., H3PMo12- nW nO40 ( n = 0–12), which are precursors of active peroxo complexes, and phase transfer catalysts Q+Br–, the catalyst H3PMo3W9O40 showed the highest activity, giving a conversion of 98% and a selectivity of 88%. By this method, a variety of water-insoluble unactivated alkenes, internal or terminal, open chain or cyclic and isolated, were epoxidised under mild conditions and after relatively short reaction times. The state of the H3PMo3W9O40/CPB/H2O2/CH3CN system was studied using UV, IR, and 31P NMR spectroscopies with the [H2O2]: [HPA] ratio = 50. Several peroxo species were observed by 31P NMR spectroscopy at a lower field than the original heteropolyacids. Their composition varied regularly with that of the starting catalyst. The P-containing peroxo species formed were deduced as [(PO4){Mo4– xW xO20}]3- ( x = 0-4), which are the true catalytically active species under the reaction conditions.