Carvone from spearmint oil

In this experiment, you will compare ( + )-carvone from caraway oil to (—)-carvone from spearmint oil, using gas chromatography. If you have the proper preparative-scale gas-chromatographic equipment, it should be possible to prepare pure samples of each of the carvones from their respective oils. If this equipment is not available, the instructor will provide pure samples of the two carvones obtained from a commercial source, and any gas-chromatographic work will be strictly analytical. 

FIGURE 1-23 Stereoisomers distinguishable by smell and taste in humans, (a) Two stereoisomers of carvone R) carvone (isolated from spearmint oil) has the characteristic fragrance of spearmint (S)-carvone (from caraway seed oil) smells like caraway, (b) Aspartame, the artificial sweetener sold under the trade name NutraSweet, is easily distinguishable by taste receptors from its bitter-tasting stereoisomer, although the two differ only in the configuration at one of the two chiral carbon atoms. 

This procedure is relatively easy for collecting the carvone component of both oils and for collecting the limonene in caraway oil. Because of the presence of several terpenes in spearmint oil, it is somewhat more difficult to isolate a pure sample of limonene from spearmint oil (see the chromatogram in the introductory section of this experiment). In this case, you must try to collect only the limonene component and not any other compounds, such as the terpene, which produces a shoulder on the limonene peak in the chromatogram for spearmint oil. 

Odor. Compare the odor of the carvone obtained from spearmint oil with that of the carvone from caraway seed oil. 

Carvone is found naturally in many essential oils, but it is most abundant in the oils from caraway and dill seeds [(S)-(-i-)-carvone] and spearmint oil [(/ )-(—)-carvone] [153]. However, the most commercially used carvone is produced from limonene. Both carvones are employed in the food and flavor industry. 

Carvone obtained from spearmint oil is the (/ )-(—) enantiomer. Explain the meaning of both terms within parentheses. 

Natural molecules are almost invariably chiral, so all types of biological receptors—taste, odor, and drug receptors—are also chiral. This means that enantiomers interact differently with these receptors. For example, i -limonene, 7.59, is derived from citrus peel and has an odor of oranges. By contrast, 5-limonene is obtained from Douglas fir needle oil and smells of turpentine/pine. / Carvone, 7.60, has the odor of spearmint and is extracted from spearmint oil. S-Carvone is extracted from dill seeds and smells of caraway. Menthol, 7.61, is a... 

Limonene (+15) is an important raw material for producing (-)-carvone [6485-40-1]. The process uses nitrosyl chloride and proceeds via nitrosochloride and oxime (78,79). The (-)-carvone (40) is found as the main component of spearmint oil and the (+)-carvone produced from (—)-limonene has the characteristic odor of diU. 

Carvone is the major constituent of spearmint oil. What products would you expect from reaction of carvone with the following reagents ... 

The main constituents of spearmint oil are /-carvone (Fig. 13.12.7) and /-limonene (Fig. 13.12.8). Oil of spearmint contains from 45 to 60% l-carvone, 6 to 20% of alcohols, and 4 to 20% of esters and terpenes, mainly /-limonene and cineole (see Fig. 13.12.4)J2J The optically isomeric form of carvone, d-carvone, is found in oil of caraway and oil of dill. Carvone appears to co-occur with limonene when present in a plant. 

Both enantiomeric forms of carvone are readily available. /-(-)-Carvone (20) is the major constituent of spearmint oil from Mentha spicata, whereas 6/-(+)-car-vone is a major constituent of caraway oil from the fruit of Carum cami or dill from the fruit of Anethum graveolens. t/Z-Carvone is found in gingergrass oils. 

Carvone is the principal odour component of spearmint oil. Both the oil and synthetic 1-carvone are used as ingredients in mint flavours. The synthetic material is made from d-limonene, which is the major component of orange oil and therefore is available as a by-product of orange juice production. Quest International is the world s major producer of 1-carvone. The classical chemistry used to produce 1-carvone is shown in Figure 4.19. The chirality of the carvone is crucial to the odour, since the enantiomeric d-carvone has an odour reminiscent of dill or caraway rather than spearmint. It is therefore important that any... 

Infrared Spectroscopy Obtain the infrared spectrum of the (—)-carvone sample from spearmint or of the (+)-carvone sample from caraway (see Technique 25, Section 25.2). Compare your result with that of a person working with the other isomer. At the option of the instructor, obtain the infrared spectrum of the (+)-limonene, which is found in both oils. If possible, determine all spectra using neat samples. If you isolated the samples by preparative gas chromatography, it may be necessary to add one to two drops of carbon tetrachloride to the sample. Thoroughly mix the liquids by drawing the mixture into a Pasteur pipette and expelling several times. It may be helpful to draw the end of the pipette to a narrow tip in order to withdraw all the liquid in the conical vial. As an alternative, use a microsyringe. Obtain a spectrum on this solution, as described in Technique 25, Section 25.2. 

Inject 50 fxL of caraway or spearmint oil on the gas-chromatography column. Just before a component of the oil (limonene or carvone) elutes from the column, install a gas-collection tube at the exit port, as described in Technique 22, Section 22.11. To determine when to connect the gas-collection tube, refer to the chromatograms prepared by your instructor. These chromatograms have been run on the same instrument you are using under the same conditions. Ideally, you should connect the gas-collection tube just before the limonene or carvone elutes from the column and remove the tube as soon as all the component has been collected but before any other compound begins to elute from the column. You can accomplish this most easily by watching the recorder as your sample passes through the column. The collection tube is connected (if possible) just before a peak is produced or as soon as a deflection is observed. When the pen returns to the baseline, remove the gas collection tube. 

Elze, after removing the carvone from a German spearmint oil, obtained an oil with a more intense spearmint odour than the original oil. It had a specific gravity 0 917 and optical rotation - 28. It contained 18 per cent, of esters and on fractionation yielded the follow-in g results —... 

The molecule carvone (14.3) is interesting because the two enantiomers have different plant origins and very different tastes. i -Carvone is the main taste constituent of spearmint oil, but S-carvone is obtained from caraway seed oil. Camphor (14.4) comes from the wood of the camphor laurel and is widely used in Asia in cooking and religious ceremonies. 

Other ketones considered in this section are sabinaketone from sabinene, camphe-nilone from camphene, and 4-methylcyclohex-3-en-l-one from terpinolene. In addition we will discuss the reactions of camphor, which is emitted directly into the atmosphere from certain trees and grasslands, carvone, a component of, for example, spearmint oil, and a number of fragrance compounds. 

A useful synthesis (ref.ll)of patchouli alcohol, an important fragrant constituent of patchouli oil, from (+)-camphor, that onetime important natural product which was employed as a plasticiser for nitrocellulose (itself a semi-synthetic polymer), was complicated by structural revision of the sesquiterpene alcohol. Dihydrocarvone (14) obtained by saturation of the ring double bond in carvone, a major constituent of oil of spearmint has been employed for two very different sesquiterpenes, the ketone campherenone (15) and the alcohol, occidentalol (16). In the first case an enol acetate was converted to a bicyclic intermediate by earlier established methodology and the route emulated a plausible biogenetic sequence giving racemic campherenone (ref.12) as shown. Any chirality in (14) is apparently lost. 

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