A PROCESS FOR THE PREPARATION OF (-) MENTHONE AND (+)-ISOMENTHONE

摘要

A process for the preparation of (-)-menthone and (+)-isomenthone of structural formulae I and II, respectively, of the accompanying drawing from a mixture of (+ )-p-menth-3-ene and (+)-p-menth-2-enes of structural formulae III and IV, respectively, of the accompanying drawing, which comprises (step a): treatment of the mixture of (+)-p-menth-3-ene and (+)-p-menth-2-enes with an organic peroxy acid prepared in situ such as herein described, in a solvent as the reaction medium and at a temperature such as herein described (the epoxidation reaction) to preferentially oxidise ( + )-p-menth-3-ene to ( + )-p-menthane-3,4-epoxide of structural formula V of the accompanying drawing and leaving (+)-p-menth-2-enes unchanged in the mixture;(step b): treatment of the resulting mixture of (+)-p-menthane-3,4-epoxide and unchanged ( + )-p-menth-2-enes with an acid catalyst such as herein described, to give essentially, a mixture of p-menthane-3,4-diol of structural formula VI of the accompanying drawing and unchanged ( + )-p-menth-2-enes which when re fluxed with the aqueous acid undergoes rearrangement to finally furnish a mixture of (- )-menthone and (+)-iso-aenthone and unchanged (+)-p-menth-2-enes and (step c): isolation of (-)-menthone and (+)-iso-menthone and unchanged (+)-p-menth-2-enes from the mixture by fractional distillation.