Method for manufacturing optically active menthol

A method for manufacturing an optically active menthol, comprising the following steps:

• A-3) asymmetrically hydrogenating at least one of geranial and neral to thereby obtain an optically active citronellal,
• B-3) conducting a ring-closure reaction of the optically active citronellal in the presence of an acid catalyst to thereby obtain an optically active isopulegol,
• D-3) recrystallizing the optically active isopulegol by deep cooling to thereby obtain the isopulegol having an increased purity, and
• E-3) hydrogenating the optically active isopulegol obtained in step D-3 to thereby obtain an optically active menthol.

A method for manufacturing an optically active menthol, comprising the following steps:

• A-4) asymmetrically hydrogenating citral containing geranial and neral at a molar ratio of from 90:10 to 10:90 to thereby obtain an optically active citronellal,
• B-4) conducting a ring-closure reaction of the optically active citronellal in the presence of an acid catalyst to thereby obtain an optically active isopulegol,
• D-4) recrystallizing the optically active isopulegol by deep cooling to thereby obtain the isopulegol having an increased purity, and
• E-4) hydrogenating the optically active isopulegol obtained in step D-4 to thereby obtain an optically active menthol.