Chemoselective catalysis by sulphated zirconia in O-alkylation of guaiacol with cyclohexene

Abstract

Alkylation of guaiacol(2-methoxyphenol) with cyclohexene gives both O- and C-alkylated products. The O-alkylated product 1-cyclohexyloxy-2-methoxybenzene(cyclohexyl-2-methoxyphenyl ether) is used as a perfumery compound. The current work was aimed at achieving maximum selectivity for this product by using an active catalyst with minimum separation cost. It covers the use of a variety of solid acid catalysts such as sulphated zirconia, Amberlyst-15, Filtrol-24, Indion-130, 20% (w/w) dodecatungstophosphoric acid supported on K-10 clay (DTP/K-10) and 20% (w/w) cesium-modified dodecatungstophosphoric acid supported over K-10 clay (Cs_2.5H_0.5PW₁₂O₄₀/K-10). Sulphated zirconia was found to be the best catalyst to achieve maximum selectivity for the ether. The O-alkylation versus C-alkylation selectivity was not only highly temperature sensitive but also the pore size and nature of acidic sites also played an important role. The reaction was carried out without using solvent. No oligomerisation of cyclohexene was formed over the temperature range employed. A suitable kinetic model is proposed and validated.