Selective etherification of β-citronellene catalyzed by zeolite beta

Abstract

The etherification of β-citronellene with bioalcohols over zeolite beta was performed in a continuous flow liquid phase reactor. At 80 °C, the catalyst exhibits 50% β-citronellene conversion with a high selectivity for the etherification reaction. High chemoselectivity (90%) at the β-double bond of β-citronellene was observed, while β-citronellene isomers were formed as minor products. In order to rationalize the observed chemoselectivity, the relative stabilities of the protonated reaction intermediates were estimated using theoretical calculations. The zeolite beta catalyst exhibits high stability as well as low coke formation. Considering the industrial importance of terpene ethers as sophisticated solvents, fragrance or flavor additives, a novel and environmentally friendly synthesis is presented as an alternative to homogeneous catalysis using strong Brønsted or Lewis acids in solution.