Carvone is a member of a family of chemicals called .
Uses
Food applications
Both carvones are used in the food and flavor industry. As the compound most responsible for the flavor of caraway, dill, and spearmint, carvone has been used for millennia in food.
Food applications are mainly met by carvone made from limonene.
R-(−)-Carvone is also used for air freshening products and, like many
essential oils, oils containing carvones are used in
aromatherapy and alternative medicine.
Agriculture
S-(+)-Carvone is also used to prevent premature sprouting of potatoes during storage, being marketed in the Netherlands for this purpose under the name
Talent.
Insect control
R-(−)-Carvone has been approved by the U.S. Environmental Protection Agency for use as a mosquito repellent.
Stereoisomerism and odor
Carvone has two mirror image forms, or
enantiomers:
R-(−)-carvone, the sweetish minty smell of
spearmint leaves. Its mirror image,
S-(+)-carvone, has a spicy aroma with notes of rye, and gives
caraway seeds their smell.
The fact that the two enantiomers are perceived as smelling different is evidence that olfactory receptors must respond more strongly to one enantiomer than to the other. Not all enantiomers have distinguishable odors. have also been found to be able to discriminate between carvone enantiomers.
The two forms are also referred to, in older texts, by their optical rotations of Levorotation referring to R-(−)-carvone, and Dextrorotation referring to S-(+)-carvone. Modern naming refers to levorotatory isomers with the sign (−) and dextrorotatory isomers with the sign (+) in the systematic name.
Occurrence
S-(+)-Carvone is the principal constituent (60–70%) of the oil from caraway seeds (
Carum carvi),
[Hornok, L. Cultivation and Processing of Medicinal Plants, John Wiley & Sons, Chichester, UK, 1992.] which is produced on a scale of about 10 tonnes per year.
[ It also occurs to the extent of about 40–60% in dill seed oil (from Anethum graveolens), and also in mandarin orange peel oil. R-(−)-Carvone is also the most abundant compound in the essential oil from several species of mint, particularly spearmint oil ( Spearmint), which is composed of 50–80% R-(−)-carvone.][[1] , Chemical composition of essential oil from several species of mint ( Mentha spp.)] Spearmint is a major source of naturally produced R-(−)-carvone. However, the majority of R-(−)-carvone used in commercial applications is synthesized from R-(+)-limonene.
History
Caraway was used for medicinal purposes by the ancient Romans,[ but carvone was probably not isolated as a pure compound until Franz Varrentrapp (1815–1877) obtained it in 1849.][ Handwörterbuch der reinen und angewandten Chemie Concise (Braunschweig, (Germany): Friedrich Vieweg und Sohn, 1849), vol. 4, pages 686-688. Notes:] It was originally called carvol by Schweizer. Goldschmidt and Zürrer identified it as a ketone related to limonene,[Heinrich Goldschmidt and Robert Zürrer (1885) "Ueber das Carvoxim," Berichte der Deutschen Chemischen Gesellschaft, 18 : 1729–1733.] and the structure was finally elucidated by Georg Wagner (1849–1903) in 1894.[Georg Wagner (1894) "Zur Oxydation cyklischer Verbindungen" (On the oxidation of cyclic compounds), Berichte der Deutschen chemischen Gesellschaft zu Berlin, vol. 27, pages 2270-2276. Notes:.); (2) Wagner did not prove the structure of carvone in this paper; he merely proposed it as plausible; its correctness was proved later.]]
Preparation
Carvone can be obtained from natural sources but insufficient is available to meet demand. Instead most carvone is produced from limonene.
The dextro-form, S-(+)-carvone is obtained practically pure by the fractional distillation of caraway oil. The levo-form obtained from the oils containing it usually requires additional treatment to produce high purity R-(−)-carvone. This can be achieved by the formation of an addition compound with hydrogen sulfide, from which carvone may be regenerated by treatment with potassium hydroxide followed by steam distillation.
Carvone may be synthetically prepared from limonene by first treating limonene nitrosyl chloride. Heating this nitroso compound gives carvoxime. Treating carvoxime with oxalic acid yields carvone.
The major use of d-limonene is as a precursor to S-(+)-carvone. The large scale availability of orange rinds, a byproduct in the production of orange juice, has made limonene cheaply available, and synthetic carvone correspondingly inexpensively prepared.[Karl-Georg Fahlbusch, Franz-Josef Hammerschmidt, Johannes Panten, Wilhelm Pickenhagen, Dietmar Schatkowski, Kurt Bauer, Dorothea Garbe, Horst Surburg "Flavors and Fragrances" in Ullmann's Encyclopedia of Industrial Chemistry, 2002, Wiley-VCH, Weinheim ]
The biosynthesis of carvone is by oxidation of limonene.
Chemical properties
Reduction
There are three double bonds in carvone capable of reduction; the product of reduction depends on the reagents and conditions used.
Oxidation
Redox reaction of carvone can also lead to a variety of products.
Conjugate additions
As an enone, carvone undergoes conjugate additions of nucleophiles. For example, carvone reacts with Gilman reagent to place a methyl group trans to the isopropenyl group with good stereoselectivity. The resulting enolate can then be allylated using allyl bromide to give ketone 11.
Other
Being available inexpensively in enantiomerically pure forms, carvone is an attractive starting material for the asymmetric total synthesis of natural products. For example, ( S)-(+)-carvone was used to begin a 1998 synthesis of the terpenoid quassin:[(a) Shing, T. K. M.; Jiang, Q; Mak, T. C. W. J. Org. Chem. 1998, 63, 2056-2057. (b) Shing, T. K. M.; Tang, Y. J. Chem. Soc. Perkin Trans. 1 1994, 1625]
In 1908, it was reported that exposure of carvone to "Italian sunlight" for one year gives carvone-camphor.
Metabolism
In the body, in vivo studies indicate that both enantiomers of carvone are mainly metabolized into dihydrocarvonic acid, carvonic acid and uroterpenolone.
External links
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Carvone at The Periodic Table of Videos (University of Nottingham)
