Catalytic rearrangement of alpha pinene oxide using spinning disc reactor technology

Abstract

This investigation explores the use of environmentally friendly solid acid catalysts based on immobilised Lewis acids in liquid phase organic reaction using the spinning disc reactor. The reaction studied was the rearrangement of a-pinene oxide to campholenic aldehyde, which is an important intermediate used by the fragrance industry in the synthesis of santalol (sandalwood). By focusing on liquid phase reactions and by addressing the particular problems associated with catalysis for such reaction systems the aim of this work is to develop new catalytic technology of value to the highly successful UK fine and speciality chemical industries, where acid catalysis is widely used but normally involves the use of corrosive and toxic reagents, unselective processes and the production of unacceptable levels of hazardous waste. The performance of a compact catalytic spinning disc reactor (SDR) with good heat and mass transfer characteristics for continuous conversion of a-pinene oxide to campholenic aldehyde using supported Zn(OTf)2 catalysts was studied. The spinning disc runs were performed at various conditions and conversion and selectivity were monitored. A 100% conversion of a-pinene oxide was easily achieved for most of the conditions. Lower residence time enhanced selectivity towards aldehyde up to a maximum of 82%, at 60% conversion. SDR empirical models were developed and activation energies determined for each catalyst used. Comparison of SDR with batch process is also made. Results suggest that the catalytic SDR can significantly enhance the reaction rates, reaction selectivity and improve process safety whilst eliminating the loss of catalyst. The findings of this investigation indicate that the vision of realising a truly intensified plant using green chemistry to achieve greener technology is a real possibility.