Wikipedia:WikiProject Chemicals/Chembox validation/VerifiedDataSandbox and Menthone: Difference between pages

| Verifiedfields = changed

| Watchedfields = changed

| verifiedrevid = 462248420

| Name = Menthone

| ImageFile = Menthone.png

| ImageName = ''l''-Menthone

| IUPACName = (2''S'',5''R'')-2-Isopropyl-5-methylcyclohexanone

| OtherNames = ''l''-Menthone

|Section1={{Chembox Identifiers

| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}

| ChEMBL_Ref = {{ebicite|correct|EBI}}

| CASNo_Ref = {{cascite|changed|scifinder}}

| CASNo = 89-80-5

| UNII_Ref = {{fdacite|changed|FDA}}

| UNII = 9NH5J4V8FN

| ChEBI_Ref = {{ebicite|correct|EBI}}

|Section2={{Chembox Properties

| C=10 | H=18 | O=1

| Density = 0.895 g/cm³

| MeltingPtC = −6

| BoilingPtC = 207

'''Menthone''' is a [[terpene|monoterpene]] with a minty flavor<ref>{{Cite book|url=https://books.google.com/books?id=9I29BwAAQBAJ&pg=PA277|title=Nutrition and Sensation|last=Hirsch|first=Alan R.|date=2015-03-18|publisher=CRC Press|isbn=9781466569089|pages=277|language=en}}</ref> that occurs naturally in a number of [[essential oil]]s. ''l''-Menthone (or (2''S'',5''R'')-''trans''-2-isopropyl-5-methylcyclohexanone), shown at right, is the most abundant in nature of the four possible [[stereoisomer]]s.<ref>{{Cite book|url=https://books.google.com/books?id=5oIj0GoS3i4C&pg=PA64|title=Handbook of Chiral Chemicals, Second Edition|last=Ager|first=David|date=2005-10-21|publisher=CRC Press|isbn=9781420027303|pages=64|language=en}}</ref> It is structurally related to [[menthol]], which has a secondary [[Alcohol (chemistry)|alcohol]] in place of the [[Carbonyl group|carbonyl]]. Menthone is used in flavoring, perfume and cosmetics for its characteristic aromatic and minty odor.

== Occurrence ==

Menthone is a constituent of the essential oils of [[Mentha pulegium|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: (2''S'',5''S''), (2''R'',5''S''), (2''S'',5''R'') and (2''R'',5''R''). 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–trans isomerism|cis]]'' conformation. These stereoisomers are called isomenthone.<ref name=":0">{{Cite book|url=https://books.google.com/books?id=Gr7jDZ8WhVUC&pg=PA41|title=Chemistry of Terpenoids and Carotenoids|last=Singh|first=G.|date=2007|publisher=Discovery Publishing House|isbn=9788183562799|pages=41|language=en}}</ref> The trans-isomers are called menthone. Because the (2''S'',5''R'') isomer has negative optical rotation, it is called ''l''-menthone or (−)-menthone. It is the [[Enantiomer|enantiomeric partner]] of the (2''R'',5''S'') isomer: (+)- or ''d''-menthone. Menthone can easily be converted to isomenthone and vice versa via a reversible [[Epimer|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.<ref>{{Cite book|url=https://books.google.com/books?id=nxO7xkQ0wFsC&pg=PT339|title=Kirk-Othmer Chemical Technology of Cosmetics|last=Kirk-Othmer|date=2012-11-27|publisher=John Wiley & Sons|isbn=9781118518908|pages=339|language=en}}</ref>

In the laboratory, ''l''-menthone may be prepared by [[oxidation]] of menthol with acidified [[dichromate]].<ref>{{OrgSynth |title = ''l''-Menthone | author = L. T. Sandborn | volume = 9 | pages = 59 | collvol = 1 | collvolpages = 340 | prep = cv1p0340| year = 1929}}</ref> 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.<ref>{{Cite journal | author = [[Herbert Charles Brown]], Chandra P. Garg, Kwang-Ting Liu | date = 1971 | title = The oxidation of secondary alcohols in diethyl ether with aqueous chromic acid. A convenient procedure for the preparation of ketones in high epimeric purity | journal = J. Org. Chem. | volume = 36 | issue = 3 | pages = 387–390 | doi = 10.1021/jo00802a005}}</ref>

== History ==

Menthone was first described by Moriya in 1881.<ref>{{cite journal

| title = Contributions from the Laboratory of the University of Tôkiô, Japan. No. IV. On menthol or peppermint camphor

| author = M. Moriya

| journal = [[Journal of the Chemical Society|Journal of the Chemical Society, Transactions]]

| year = 1881

| volume = 39

| pages = 77–83

| doi = 10.1039/CT8813900077

| url = https://zenodo.org/record/1680417

}}</ref><ref name="read">{{cite journal

| title = Recent Progress in the Menthone Chemistry.

| author = John Read

| journal = [[Chemical Reviews]]

| year = 1930

| volume = 7

| issue = 1

| pages = 1–50

| doi = 10.1021/cr60025a001

}}</ref> 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.<ref name=":0" />

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.<ref>{{cite journal

| title = Untersuchungen in der Campherreihe

| author = Ernst Beckmann

| journal = [[Liebigs Annalen]]

| year = 1889

| volume = 250

| issue =3

| pages = 322–375

| doi = 10.1002/jlac.18892500306

| author-link = Ernst Beckmann

| url = https://zenodo.org/record/1427429

}}</ref> 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 ==

<!-- * ''Merck Index'', 12th Edition, '''5883'''. -->

<references/>

[[Category:Flavors]]

[[Category:Cooling flavors]]

[[Category:Ketones]]

[[Category:Perfume ingredients]]

[[Category:Monoterpenes]]

[[Category:Isopropyl compounds]]

[[Category:Cyclohexanes]]