(–)-Menthol

December 26, 2016
Happy holidays from one of your favorite flavors.
What molecule am I?

Menthol is a substituted cyclohexanol that is familiar to many as the main constituent of mint. It occurs in peppermint and other mint oils. (–)-Menthol is far more common in nature than its (+)- enantiomer. The molecule has three stereogenic centers, leading to other isomers known as isomenthol, neomenthol, and isoneomenthol.

Racemic synthetic menthol is made by hydrogenating the phenolic compound thymol. The hydrogenation produces all of the stereoisomers; (–)-menthol is isolated by esterification, fractional crystallization, and hydrolysis.

Menthol is a component of a wide range of over-the-counter remedies. It triggers cold-sensitive receptors in human tissues, making it useful in dental products, sunburn medications, shaving creams, and decongestants. It is a flavoring agent in foods such as ice cream, tea, candy, and liqueurs.

So while you suck on your holiday candy cane, think good thoughts about (–)-menthol and its seven isomeric cousins.

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