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

摘要

A process for the preparation of (minus;)=menthone and (plus;)=isomenthone of structural formula I and II, respectively of the accompanying drawing from a mixture of (plus;)-p-menth-3-ene and (plus;)-p-menth-2-ene of structural formula III and IV, respectively, of the accompanying drawing which comprises (step a): treatment of the mixture of (plus;)-p-menth-3-enes and (plus;)-p-menth-2-enes with a performed organic peroacid such as herein described (the epoxidation reaction) preferentially oxidize (plus;)-p-menth-3-ene to (plus;)-p-menthane-3, 4-epoxide of structural Formula V, of the accompanying drawing and leaving (plus;)-p-menth-2-enes unchanged in the mixture; (step b) : treatment of the resulting mixture of p-menthane-3, 4-epoxide and unchanged (plus;)-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 (plus;)-p-menth-2-enes which when refluxed with a aqueous acid undergoes rearrangement to finally furnish a mixture of (minus;)=menthone and (plus;)=isomenthone and unchanged (plus;)-p-menth-2-enes and (step c): isolation of (minus;)=menthone and (plus;)=isomenthone and unchanged (plus;)-p-menth-2-enes by fraction distillation.