Exploring structure activity relationships in the acetoxylation of small olefins

The diacetoxylation of butadiene in the liquid phase is part of an industrially established interesting alternative route to tetrahydrofurane (THF) competing with the currently most attractive route of butane oxidation to maleic anhydride and subsequent hydrogenation to THF. Although successfully executed in the liquid phase, no viable gas phase process has been realised for the diacetoxylation of butadiene until today. In this paper we present our results on screening campaigns focussed on Pd–K–X–Y libraries tested in a 192-fold reactor system for the acetoxylation of butadiene, butenes, propene and ethylene. An in depth analysis of the compositional space with the Pd–K–X–Y systems was conducted together with a sensitivity analysis regarding the feed constituents butadiene, acetic acid and oxygen. In the screening campaign we could identify a new catalyst system based on Pd–K–Bi–Pt which outperforms all other catalysts tested especially in the diacetoxylation of butadiene and the acetoxylation of ethylene. Based on the results obtained we also propose an alternative mechanistic pathway for the acetoxylation which proceeds via radicals as intermediates. The alternative mechanism is supported by our results obtained on quantum mechanical calculations.