Menthone
| l-Menthone | |
|---|---|
| |
| IUPAC name | (2S,5R)-2-Isopropyl-5-methylcyclohexanone |
| Other names | l-Menthone |
| Identifiers | |
| InChI | InChI=1/C10H18O/c1-7(2)9-5-4-8(3)6-10(9)11/h7-9H,4-6H2,1-3H3/t8-,9+/m1/s1 |
| InChIKey | NFLGAXVYCFJBMK-BDAKNGLRBF |
| Standard InChI | InChI=1S/C10H18O/c1-7(2)9-5-4-8(3)6-10(9)11/h7-9H,4-6H2,1-3H3/t8-,9+/m1/s1 |
| Standard InChIKey | NFLGAXVYCFJBMK-BDAKNGLRSA-N |
| CAS number | [] |
| EC number | |
| ChemSpider | |
| SMILES | |
| Properties[1] | |
| Chemical formula | C10H18O |
| Molar mass | 154.25 g/mol |
| Density | 0.895 g/cm3 |
| Melting point |
−6 °C |
| Boiling point |
207 °C |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) | |
Menthone is a naturally occurring organic compound with a molecular formula C10H18O. l-Menthone (or (2S, 5R)-trans-2-isopropyl-5-methylcyclohexanone), shown at right, is the most abundant in nature of the four possible stereoisomers. Menthone is a monoterpene and a ketone. It is structurally related to menthol which has a secondary alcohol in place of the carbonyl.
Menthone is used in perfumery and cosmetics for its characteristic aromatic and minty odor.
Occurrence
Menthone is a constituent of the essential oils of pennyroyal, peppermint, Pelargonium geraniums, and others. In most essential oils, it is a minor compound. This is the cause for the fact that it was first synthesized by oxidation of menthol in 1881 before it was found in essential oils in 1891.
Preparation
Menthone is cheaply available as a mixture of isomers; when enantiopure, it costs significantly more. In the laboratory, l-menthone may be prepared by oxidation of menthol with acidified dichromate.[2]
History
Menthone was first described by Moriya in 1881.[3][4] It was then synthesized by heating menthol with chromic acid.
Menthone was crucial to one of the great mechanistic discoveries in organic chemistry. In 1889, Ernst Beckmann discovered that dissolving menthone in concentrated sulfuric acid gave a new ketonic material. Coincidentally, the product gave an equal but opposite optical rotation to the starting material.[5] The tetrahedral carbon having been recognized for only 15 years at that time, Beckmann realized that this must result from an inversion of configuration at the asymmetric carbon atom next to the carbonyl group (at that time thought to be carbon attached to the methyl, rather than the isopropyl group), and he postulated this as happening through the intermediacy of an enol tautomer in which the asymmetric carbon atom was of trigonal (planar) rather than of tetrahedral geometry. This was an early example of the inference of an (almost) undetectable intermediate in a reaction mechanism accounting for the outcome of the reaction.
References
- ↑ The Merck Index: An Encyclopedia of Chemicals, Drugs, and Biologicals, 12th ed.; Budavari, Susan, Ed.; Merck, 1996. ISBN 0911910123, 5883.
- ↑ Sandborn, L. T. l-Menthone. Org. Synth. 1929, 9, 59, <http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv1p0340>; Coll. Vol., 1, 340.
- ↑ Moriya, M. Contributions from the Laboratory of the University of Tôkiô, Japan. No. IV. On menthol or peppermint camphor. J. Chem. Soc., Trans. 1881, 39, 77–83. DOI: 10.1039/CT8813900077.
- ↑ Read, John Recent Progress in the Menthone Chemistry. Chem. Rev. 1930, 7 (1), 1–50. DOI: 10.1021/cr60025a001.
- ↑ Beckmann, Ernst Untersuchungen in der Campherreihe. Justus Liebigs Ann. Chem. 1889, 250 (3), 322–75. DOI: 10.1002/jlac.18892500306.
External links
- WHO Food Additives Series 42: Substances Structurally Related to Menthol
- Molecular modelling experiment involving menthone
- 1H and 13C NMR spectra at ChemSpider
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