The effect of ring size on the selective oxidation of cycloalkenes using supported metal catalysts

Abstract

In this work we expand on our previous studies on the oxidation of cyclic alkenes using supported gold nanoparticles together with catalytic amounts of peroxides. We demonstrate that various sized cyclic alkenes can be oxidised by this catalyst, under green conditions, without solvent and using air as the oxidant gas. The effect of support, preparation method and choice of metal have been investigated, we demonstrate that supported gold is superior to palladium or a gold palladium alloy, we show that oxides provide the best support for these gold catalysts and the preparation methods that afford the smallest particles are the most active. We show that the reactivity of the cyclic alkenes is related to the ring size with the smaller rings more reactive than the larger rings at the same temperature. The selectivity to the epoxide is dependent on the size of the cyclic alkene ring. In particular, the epoxide selectivity is very low for rings containing fewer than seven carbon atoms. We discuss the origins of this selectivity effect, using DFT calculations to investigate the effect of ring strain on the intermediates and reaction products.