PROCESS FOR PREPARING (-) MENTHOL AND SIMILAR COMPOUNDS

Abstract

A process of separating a desired (−) stereoisomer which is selected from (−) menthol or an equivalent (−) compound where the isopropyl group is replaced with an isopropanol or an isopropylene group, from a starting material comprising: 40 to 100 m/m % of a mixture of (−)-menthol and (+)-menthol; up to 30 m/m % of a mixture of (−)-isomenthol and (+)-isomenthol; up to 20 m/m % of a mixture of (−)-neomenthol and (+)-neomenthol; and up to 10 m/m % of a mixture of (−)-neoisomenthol and (+)-neoisomenthol or an equivalent (+) mixture where the isopropyl group is replaced with an isopropanol or an isopropylene group, includes the steps of: contacting the starting material with an esterifying agent and a stereospecific enzyme which is a Pseudomonas lipase enzyme which stereoselectively esterifies the —OH group of the desired (−) steroisomer, for a time sufficient to convert a desired percentage of the desired (−) stereoisomer to a desired (−) esterified compound where the —OH group is converted to a group —O—C(O)—R4, wherein R4 is an alkyl or an aryl group, to give a first reaction product including the desired (−) esterified compound, the organic solvent, the unconverted stereoisomers, excess esterifying agent and by-products of the reaction; and separating the desired (−) esterified compound from the first reaction product. The process is of particular application for the production of (−)-menthol.