Menthone
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IUPAC name
(2S,5R)-2-Isopropyl-5-methylcyclohexanone
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Other names
l-Menthone
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Identifiers | |
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Properties | |
C10H18O | |
Molar mass | 154.253 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).
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Menthone is a
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; it was first synthesized by oxidation of menthol in 1881 before it was found in essential oils in 1891.
Structure and preparation
2-Isopropyl-5-methylcyclohexanone has two asymmetric carbon centers, meaning that it can have four different stereoisomers: (2S,5S), (2R,5S), (2S,5R) and (2R,5R). The S,S and R,R stereoisomers have the methyl and isopropyl groups on the same side of the cyclohexane ring: the so-called cis conformation. These stereoisomers are called isomenthone.[3] The trans-isomers are called menthone. Because the (2S,5R) isomer has negative optical rotation, it is called l-menthone or (−)-menthone. It is the enantiomeric partner of the (2R,5S) isomer: (+)- or d-menthone. Menthone can easily be converted to isomenthone and vice versa via a reversible epimerization reaction via an enol intermediate, which changes the direction of optical rotation, so that l-menthone becomes d-isomenthone, and d-menthone becomes l-isomenthone.[4]
In the laboratory, l-menthone may be prepared by
History
Menthone was first described by Moriya in 1881.[7][8] It was then synthesized by heating menthol with chromic acid, and its structure was later confirmed by synthesizing it from 2-isopropyl-5-methylpimelic acid.[3]
Menthone was crucial to one of the great mechanistic discoveries in organic chemistry. In 1889,
References
- ISBN 9781466569089.
- ISBN 9781420027303.
- ^ ISBN 9788183562799.
- ISBN 9781118518908.
- ^ L. T. Sandborn (1929). "l-Menthone". Organic Syntheses. 9: 59; Collected Volumes, vol. 1, p. 340.
- doi:10.1021/jo00802a005.)
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