Selective oxidation of alkenes using graphite-supported gold-palladium catalysts
Oxidation is an important route for the activation of chemical feedstocks for the synthesis of chemical intermediates. Alkene epoxidation by the electrophilic addition of oxygen to a carbon-carbon double bond is a major challenge in oxidation catalysis. In particular it is important to use molecular oxygen as the oxidant to avoid the formation of reagent by-products. We report the oxidation with air using graphite-supported gold-palladium catalysts of two alkenes, cis-cyclooctene, which gives mainly the epoxide, and crotyl alcohol (trans-but-2-en-1-ol). With cyclooctene, the reaction requires catalytic amounts of t-butyl hydroperoxide. The Au-Pd ratio has a major effect on the conversion with very low activities being associated with Au:Pd ratios of ca. 4 : 1 and 1 : 4 by weight. The selectivity to the epoxide is not affected by the Au : Pd ratio. With crotyl alcohol, t-butyl hydroperoxide was not required for activity. In the absence of Pd, crotonaldehyde was formed, but the introduction of Pd leads to an isomerisation pathway to 3-buten-1-ol being favoured over epoxidation and crotonaldehyde was a minor product.