The mechanism of hydrogenolysis and isomerization of oxacycloalkanes on metals. Part 8.—New results on the mechanism of hydrogenolysis of oxiranes on platinum and palladium

Abstract

The transformations of methyloxirane and cis- and trans-2,3-dimethyloxirane have been studied on Pt/C and Pd/C catalysts at 373 K in the hydrogen pressure range 2–70 kPa in a circulation reactor. The reactions of the dimethyloxirane isomers proceed by similar mechanisms, the rate-determining step in both cases presumably being cleavage of the C—O bond. The mechanism for methyloxirane differs from that for the dimethyloxiranes. One mechanism involves edgewise adsorption of the oxirane (probably via two non-bonding electron pairs), while the other involves flat-lying adsorption. The change in regioselectivity with increase in hydrogen pressure is caused by supression of the adsorption of oxygen via two electron pairs.