Cobalt catalyzed autoxidation of monoterpenes in acetic acid and acetonitrile solutions

Oxidation of limonene, alpha-pinene and beta-pinene with dioxygen in acetic acid and acetonitrile solutions containing catalytic amounts Of CoCl2 has been studied. Limonene and alpha-pinene give both allylic oxidation and epoxidation products in a molar ratio of near 1/1, with chemoselectivities for corresponding products being higher in acetonitrile than those in acetic acid. On the other hand, oxidation of beta-pinene leads essentially to allylic products, i.e. highly valuable pinocarveol, pinocarvone, myrtenol and myrtenal. In acetic acid, a combined selectivity for these products does not exceed 40% due to the concomitant substrate isomerization and acetic acid addition, while in acetonitrile, good selectivities of up to 85% at a 40-50% substrate conversion have been achieved. (C) 2003 Elsevier Science B.V. All rights reserved.