Menthone

Menthone
Names
IUPAC name
(2S,5R)-2-Isopropyl-5-methylcyclohexanone
Other names
l-Menthone
Identifiers
89-80-5 N[scifinder]
3D model (Jmol) Interactive image
ChEBI CHEBI:15410 YesY
ChEMBL ChEMBL276311 YesY
ChemSpider 24636 YesY
ECHA InfoCard 100.034.464
PubChem 26447
UNII 9NH5J4V8FN N
Properties
C10H18O
Molar mass 154.25 g·mol−1
Density 0.895 g/cm3
Melting point −6 °C (21 °F; 267 K)
Boiling point 207 °C (405 °F; 480 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YesYN ?)
Infobox 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.

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, Mentha arvensis, 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.[1]

If the chromic acid oxidation is performed with stoichiometric oxidant in the presence of diethyl ether as co-solvent, a method introduced by H.C. Brown, the epimerization of l-menthone to d-isomenthone is largely avoided. If menthone and isomenthone are equilibrated at room temperature, the isomenthone content will reach 29%. Pure l-menthone has an intensely minty clean aroma. By contrast, d-isomenthone has a "green" note, increasing levels of which are perceived to detract from the odor-quality of l-menthone.[2]

Usage as pesticide

Menthone is a naturally occurring pesticide[3] used in some products such as Ecosmart Roach Killer.

History

Menthone was first described by Moriya in 1881.[4][5] 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.[6] 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

  1. ↑ L. T. Sandborn (1929). "l-Menthone". Org. Synth. 9: 59.; Coll. Vol., 1, p. 340
  2. ↑ Herbert Charles Brown, Chandra P. Garg, Kwang-Ting Liu (1971). "The oxidation of secondary alcohols in diethyl ether with aqueous chromic acid. A convenient procedure for the preparation of ketones in high epimeric purity". J. Org. Chem. 36 (3): 387–390. doi:10.1021/jo00802a005.
  3. ↑ Robert Irving Krieger (2001). Handbook of Pesticide Toxicology: Principles. Academic Press. p. 823. ISBN 978-0-12-426260-7. Retrieved 11 October 2010.
  4. ↑ 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.
  5. ↑ John Read (1930). "Recent Progress in the Menthone Chemistry.". Chemical Reviews. 7 (1): 1–50. doi:10.1021/cr60025a001.
  6. ↑ Ernst Beckmann (1889). "Untersuchungen in der Campherreihe". Annalen. 250 (3): 322. doi:10.1002/jlac.18892500306.
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