|for racemic (âˆ’)-isomer||(2R)-(2-Propyl)-(5S)-methyl-
|Molar mass||156.27 g/mol|
|Appearance||White or colorless
|CAS number||[89-78-1], racemic
|Density and phase||0.890 g/cm3, solid
(racemic or (âˆ’)-isomer)
|Solubility in water||Slightly soluble, (âˆ’)-isomer|
|In ethanol, diethyl ether,
acetic acid, hexane
|Melting point||36-38 Â°C (311 K), racemic
42-45 Â°C (318 K), (âˆ’)-form (Î±)
35-33-31 Â°C, (âˆ’)-isomer
|Boiling point||212 Â°C (485 K)|
|Chiral rotation||-50Â° at 18 Â°C, 10% EtOH soln.|
|Main hazards||Irritant, flammable|
|Flash point||93 Â°C|
|RTECS number||OT0350000, racemic
|Related alcohols||Cyclohexanol, Pulegol,
|Related compounds||Menthone, Menthene,
|Except where noted otherwise, data are given for
materials in their standard state (at 25Â°C, 100 kPa)
Infobox disclaimer and references
Menthol is a covalent organic compound made synthetically or obtained from peppermint or other mint oils. It is a waxy, crystalline substance, clear or white in color, which is solid at room temperature and melts slightly above. The main form of menthol occurring in nature is (-)-menthol, which is assigned the (1R,2S,5R) configuration. Menthol has local anesthetic and counterirritant qualities, and it is widely used to relieve minor throat irritation.
There is evidence that menthol has been known in Japan for more than 2000 years, but in the west it was not isolated until 1771, by Gambius. (-)-Menthol (also called l-menthol or (1R,2S,5R)-menthol) occurs naturally in peppermint oil (along with a little menthone, the ester menthyl acetate and other compounds), obtained from mentha x piperita. Japanese menthol also contains a small percentage of the 1-epimer, (+)-neomenthol.
Menthol is included in many products for a variety of reasons. These include:
Some supporters of the homeopathic theory of pharmacology believe that menthol interferes with the effects of homeopathic remedies. Its use is strongly discouraged for those seeking homeopathic cures, to the point of prohibiting the use of mint-flavored toothpaste. Currently no other reported nutrient or herb interactions involve menthol. Menthol is available as a dietary supplement or natural medicine in the form of peppermint oil. It is used in Eastern medicine to treat indigestion, nausea, sore throat, diarrhoea, colds, and headaches. (-)-Menthol has low toxicity: Oral (rat) LD50: 3300 mg/kg; Skin (rabbit) LD50: 15800 mg/kg).
Menthol reacts in many ways like a normal secondary alcohol. It is oxidised to menthone by oxidising agents such as chromic acid, though under some conditions the oxidation can go further and break open the ring. Menthol is easily dehydrated to give mainly 3-menthene, by the action of 2% sulfuric acid. PCl5 gives menthyl chloride.