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Menthone

Menthone

IUPAC name	(2S,5R)-2-Isopropyl-5-methylcyclohexanone
Other names	l-Menthone
Identifiers
CAS number	14073-97-3
SMILES	C1(=O)[C@H](C(C)C)CC[C@@H](C)C1
Properties
Molecular 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) Infobox disclaimer and references

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.

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Menthone is a constituent of the essential oils of pennyroyal, peppermint, geranium, and others. In most essential oil it is 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. It is used in perfumery and cosmetics for its characteristic aromatic and minty odor.

This molecule is at the heart of one of the great mechanistic discoveries in organic chemistry. Ernst Beckmann in 1889 discovered that dissolving menthone in concentrated sulfuric acid gave a new ketonic material, with a (coincidentally) equal but opposite optical rotation to the starting material. With the recognition of tetrahedral carbon being only 15 years old (Jacobus Henricus van't Hoff and Joseph Achille Le Bel), 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 the methyl rather than the iso-propyl 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.

Preparation

Menthone may be prepared by oxidation of menthol with acidified dichromate.^[1]

References

The references in this article would be clearer with a different or consistent style of citation, footnoting, or external linking.

Merck Index, 12th Edition, 5883.
E. Beckmann (1889). "Untersuchungen in der Campherreihe". Annalen 250: 322. doi:10.1002/jlac.18892500306.
John Read (1930). "Recent Progress in the Menthone Chemistry.". Chemical Reviews 7 (1): 1-50. doi:10.1021/cr60025a001.
M. Moriya (1881). "Contributions from the Laboratory of the University of Tôkiô, Japan. No. IV. On menthol or peppermint camphor". Journal of the Chemical Society, Transactions 39: 77-83. doi:10.1039/CT8813900077.
For a molecular modelling experiment involving menthone, see here.

^ L. T. Sandborn. "l-Menthone". Org. Synth.; Coll. Vol. 1: 340.

Category: Terpenes and terpenoids

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Menthone". A list of authors is available in Wikipedia.