Carvone is a member of a family of chemicals called terpenoids. Carvone is found naturally in many essential oils, but is most abundant in the oils from seeds of caraway (Carum carvi), spearmint (Mentha spicata), and dill.
Uses
Both carvones are used in the food and flavor industry. R-(−)-Carvone is also used for air freshening products and, like many essential oils, oils containing carvones are used in aromatherapy and alternative medicine. S-(+)-Carvone has shown a suppressant effect against high-fat diet induced weight gain in mice.
Food applications
As the compound most responsible for the flavor of caraway, dill and spearmint, carvone has been used for millennia in food. Wrigley's Spearmint Gum and spearmint flavored Life Savers are major users of natural spearmint oil from Mentha spicata. Caraway seed is extracted with alcohol to make the European drink Kümmel.
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.
Organic synthesis
Carvone is available inexpensively in both enantiomerically pure forms, making it 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:<ref>(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.</ref>
Stereoisomerism and odor
Carvone forms two mirror image forms or enantiomers: R-(−)-carvone, has a sweetish minty smell, like spearmint leaves. Its mirror image, S-(+)-carvone, has a spicy aroma with notes of rye, like caraway seeds. 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. Squirrel monkeys 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 laevo (l) referring to R-(−)-carvone, and dextro (d) referring to S-(+)-carvone. Modern naming refers to levorotatory isomers with the sign (-) and dextrorotatory isomers with the sign (+) in the systematic name.
OccurrenceS-(+)-Carvone is the principal constituent (60–70%) of the oil from caraway seeds (Carum carvi), 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 (Mentha spicata), which is composed of 50–80% R-(−)-carvone. 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. The R-(−)-carvone isomer also occurs in kuromoji oil. Some oils, like gingergrass oil, contain a mixture of both enantiomers. Many other natural oils, for example peppermint oil, contain trace quantities of carvones.
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 dictionary of pure and applied chemistry] (Braunschweig, (Germany): Friedrich Vieweg und Sohn, 1849), vol. 4, pages 686-688. [Notes: (1) Varrentrapp purified carvone by mixing oil of caraway with alcohol that had been saturated with hydrogen sulfide and ammonia; the reaction produced a crystalline precipitate, from which carvone could be recovered by adding potassium hydroxide in alcohol to the precipitate, and then adding water; (2) Varrentrapp's empirical formula for carvone is incorrect because chemists at that time used the wrong atomic masses for the elements; e.g., carbon (6 instead of 12).] It was originally called carvol by Schweizer. Goldschmidt and Zürrer identified it as a ketone related to limonene, and the structure was finally elucidated by Georg Wagner (1849–1903) in 1894.