The deoxygenation in the catalytic hydrogenolysis of styrene oxides

Abstract

In order to obtain information on deoxygenation in the hydrogenolysis of epoxides, a series of substituted styrene oxides were hydrogenolysed using Raney Ni, Pd and Pt as catalysts. Over Raney Ni, these styrene oxides gave ethylbenzenes (30–50%) as well as 2-phenylethanols. The ethyl-benzenes were proved to be produced via the corresponding styrenes. These deoxygenations can be explained by the previously proposed mechanism involving the radical cleavage reaction. The hydrogenolyses over Pd gave selectively 2-phenylethanols. Over PtO 2, the deoxygenations were less than 10% except 3,4-dichlorostyrene oxide (V) which gave 3,4-dichloroethylbenzene in 75% yield. However, the significant deoxygenations were observed in all hydrogenolyses over Pt-black. The ethylbenzenes were proved to be produced directly from the corresponding styrene oxides, but not from 1-phenylethanols as proposed by Park and Fuchs. These deoxygenations are considered to occur via styrenes by trans-β-elimination. The difference in behaviour over Pt catalysts can be ascribed to the alkaline substances contained in the catalyst. The significant deoxygenation in the hydrogenolysis of V over PtO 2 can be explained by the effect of a trace of HCl produced from the substrate and/or products.