Menthone is a monoterpene with a minty flavor[1] that occurs naturally in a number of essential oils. l-Menthone (or (2S,5R)-trans-2-isopropyl-5-methylcyclohexanone), shown at right, is the most abundant in nature of the four possible stereoisomers.[2] It is structurally related to menthol, which has a secondary alcohol in place of the carbonyl. Menthone is used in flavoring, perfume and cosmetics for its characteristic aromatic and minty odor.
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 preparationedit
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 oxidation of menthol with acidified dichromate.[5] 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.[6]
Historyedit
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, Ernst Beckmann discovered that dissolving menthone in concentrated sulfuric acid gave a new ketonic material which gave an equal but opposite optical rotation to the starting material.[9] 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 an intermediate enol tautomer in which the asymmetry of the carbon atom was removed when it changed from a tetrahedral to a trigonal (planar) 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.
Referencesedit
^Hirsch, Alan R. (2015-03-18). Nutrition and Sensation. CRC Press. p. 277. ISBN9781466569089.
^Ager, David (2005-10-21). Handbook of Chiral Chemicals, Second Edition. CRC Press. p. 64. ISBN9781420027303.
^ abSingh, G. (2007). Chemistry of Terpenoids and Carotenoids. Discovery Publishing House. p. 41. ISBN9788183562799.
^Kirk-Othmer (2012-11-27). Kirk-Othmer Chemical Technology of Cosmetics. John Wiley & Sons. p. 339. ISBN9781118518908.
^L. T. Sandborn (1929). "l-Menthone". Organic Syntheses. 9: 59.; Collective Volume, vol. 1, p. 340
^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.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^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.
^John Read (1930). "Recent Progress in the Menthone Chemistry". Chemical Reviews. 7 (1): 1–50. doi:10.1021/cr60025a001.
menthone, monoterpene, with, minty, flavor, that, occurs, naturally, number, essential, oils, trans, isopropyl, methylcyclohexanone, shown, right, most, abundant, nature, four, possible, stereoisomers, structurally, related, menthol, which, secondary, alcohol,. Menthone is a monoterpene with a minty flavor 1 that occurs naturally in a number of essential oils l Menthone or 2S 5R trans 2 isopropyl 5 methylcyclohexanone shown at right is the most abundant in nature of the four possible stereoisomers 2 It is structurally related to menthol which has a secondary alcohol in place of the carbonyl Menthone is used in flavoring perfume and cosmetics for its characteristic aromatic and minty odor Menthone NamesIUPAC name 2S 5R 2 Isopropyl 5 methylcyclohexanoneOther names l MenthoneIdentifiersCAS Number 89 80 5 N scifinder 3D model JSmol Interactive imageChEBI CHEBI 15410 YChEMBL ChEMBL276311 YChemSpider 24636 YPubChem CID 26447UNII 9NH5J4V8FN NInChI 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 YKey NFLGAXVYCFJBMK BDAKNGLRSA N YInChI 1 C10H18O c1 7 2 9 5 4 8 3 6 10 9 11 h7 9H 4 6H2 1 3H3 t8 9 m1 s1Key NFLGAXVYCFJBMK BDAKNGLRBFSMILES O C1C C H C CC C H 1C C CPropertiesChemical formula C 10H 18OMolar mass 154 253 g mol 1Density 0 895 g cm3Melting 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 Y N Infobox references Contents 1 Occurrence 2 Structure and preparation 3 History 4 ReferencesOccurrence editMenthone 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 edit2 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 oxidation of menthol with acidified dichromate 5 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 6 History editMenthone 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 Ernst Beckmann discovered that dissolving menthone in concentrated sulfuric acid gave a new ketonic material which gave an equal but opposite optical rotation to the starting material 9 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 an intermediate enol tautomer in which the asymmetry of the carbon atom was removed when it changed from a tetrahedral to a trigonal planar 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 edit Hirsch Alan R 2015 03 18 Nutrition and Sensation CRC Press p 277 ISBN 9781466569089 Ager David 2005 10 21 Handbook of Chiral Chemicals Second Edition CRC Press p 64 ISBN 9781420027303 a b Singh G 2007 Chemistry of Terpenoids and Carotenoids Discovery Publishing House p 41 ISBN 9788183562799 Kirk Othmer 2012 11 27 Kirk Othmer Chemical Technology of Cosmetics John Wiley amp Sons p 339 ISBN 9781118518908 L T Sandborn 1929 l Menthone Organic Syntheses 9 59 Collective Volume vol 1 p 340 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 a href Template Cite journal html title Template Cite journal cite journal a CS1 maint multiple names authors list link M Moriya 1881 Contributions from the Laboratory of the University of Tokio Japan No IV On menthol or peppermint camphor Journal of the Chemical Society Transactions 39 77 83 doi 10 1039 CT8813900077 John Read 1930 Recent Progress in the Menthone Chemistry Chemical Reviews 7 1 1 50 doi 10 1021 cr60025a001 Ernst Beckmann 1889 Untersuchungen in der Campherreihe Liebigs Annalen 250 3 322 375 doi 10 1002 jlac 18892500306 Retrieved from https en wikipedia org w index php title Menthone amp oldid 1064063119, wikipedia, wiki, book, books, library,
