The present invention relates to a particularly economic overall method for producing menthol, specifically for producing optically active, essentially enantiomerically and diastereomerically pure L-menthol and racemic menthol, starting from the starting material citral which is available inexpensively on an industrial scale. The method comprises the following steps
a.1) catalytic hydrogenation of neral and/or geranial to give citronellal,
b.1) cyclization of citronellal to isopulegol in the presence of an acidic catalyst,
c.1) purification of isopulegol by crystallization and
d.1) catalytic hydrogenation of isopulegol to give menthol.
该发明涉及一种特别经济的生产薄荷醇的整体方法,具体用于生产光学活性、基本上对映异构和顺反异构纯的
L-薄荷醇和混合薄荷醇,从廉价的工业规模起始原料
柠檬醛开始。该方法包括以下步骤:a.1)将
柠檬醛和/或莰醛催化氢化得到
柠檬醛醇,b.1)在酸性催化剂存在下将
柠檬醛醇环化为
异薄荷醇,c.1)通过结晶纯化
异薄荷醇,d.1)将
异薄荷醇催化氢化得到薄荷醇。