In a surprising way, Haarmann & Reimer developed an elegant way of producing (-)-menthol that has made them the market leader in synthetic (-)-menthol.

Although racemic menthol can be resolved using classic methods, the H&R route utilizes the unexpected ability of the racemic menthyl benzoates to be separated by crystallization induced by seeding the mixture with one of the optically active menthyl benzoate enantiomers.

In what must be described as a chemical process development and engineering feat, the total process, which involves numerous recycles leads to a 90+% overall yeild.

1. Leffingwell, J.C. & R.E. Shackelford, Laevo-Menthol - Syntheses and organoleptic properties, Cosmetics and Perfumery, 89(6), 69-89, 1974

2. Hopp, R., Menthol: its origins, chemistry, physiology and toxicological properties, Rec. Adv. Tobacco Science, Vol. 19, 3-46 (1993).