Haarman and Reimer

It is the existence of the eight menthol isomers that makes the chemical synthesis onerous. In many procedures, more than one isomers form as a final product, and needs to be separated out at the end. These byproducts, the isomers of (-)-menthol, all have cooling and refreshing effects, but none of them is as potent as menthol itself. So the presence of these isomers lowers the quality of the final product. Another option is to look for a chemical reaction that produces (-)-menthol exclusively. This was achieved from meta-cresol by the company Haarman and Reimer, which is also a major vanillin producer, whereas a Japanese chemical company, Takasago,... 

H. Surburg, M. Guentert and H. Harder, in Recent Developments of Flavour and Fragrance Chemistry Proceedings of the 3rd International Haarman Reimer Symposium, R. Hopp and K. Mori (eds.), VCH Publishers, Weinheim, 1993, p. 29. 

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