Spearmint odour, -carvone

At the beginning of the 1970s there appeared works in Science and Nature concerning the relationships between odours and chirality. The authors have stated that the experimental evidence is in favour of the claim that the optical isomers of carvone have characteristically different odours, (-)-carvone resembling spearmint oil and (+)-carvone, caraway oil... 

Monoterpenic ketones are frequently very important aromatic substances of many food raw materials, spices and medicinal herbs. Monocyclic ketone (-F)-carvone (8-50) is a key component of caraway and diU oils, where it is accompanied by (-F)-( )-dihydrocarvone, that is (lS,4S)-dihydrocarvone (8-50) that also possesses caraway odour. (-)-Carvone (8-50) is a typical component of spearmint essential oil, where it is accompanied by (-)-( )-dihydrocarvone, (lE,4E)-dihydrocarvone, which has the same odour (see Table 8.32). Isomeric ( )-menthone (8-50) and its precursor (-F)-pulegone (8-50) occur in the essential oils of the European pennyroyal Menthaptdegium, Lamiaceae), a traditional culinary herb and folk remedy, and other Mentha species (such as M. longifolia), as well as in marjoram essential oil. In the essential oil of mint, (-)-menthone is accompanied by (-F)-isomenthone (8-50) and other terpenoids. 

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 major constituent of caraway oil is (+)-carvone, and the typical caraway odour is mainly due to this component. On the other hand, the typical minty smell of spearmint oil is due to its major component, (—)-carvone. These enantiomers are unusual in having quite different smells, i.e. they interact with nasal receptors quite differently. The two enantiomeric forms are shown here in their half-chair conformations. 

Carvone (94) occurs as (+)-carvone, (-)-carvone or racemic carvone. (S)-(+)-Carvone is the main component of caraway oil (ca 60%) and dill oil and has a herbaceous odour reminiscent of caraway and dill seeds. (R)-(-)-Carvone occurs in spearmint oil at a concentration of 70-80% and has a herbaceous odour similar to spearmint [26]. (S)-(+)-Carvone (94) was used as substrate for bioconversions by selected microorganisms five... 

The difference between the odours of two optical isomers of carvone has been characterised by various authors. Russell and Hills have described that 4S-carvone has the odour of caraway and 4R-carvone has the odour of spearmint. They have stated that these observations lend a definite support to stereochemical considerations of odour pereeption... 

Q8. (-)-Carvone (73) occurs in spearmint and its enantiomer (+)-carvone (74) is found in caraway seed. To the human sense of smell, these two enantiomers have different odours. Where is the stereogenic centre in 73 and in 74 What conclusions can be drawn about the human olfactory receptor site ... 

Carveol (5) is one of the minor components responsible for the odour of spearmint, and is easily prepared by reduction of carvone. Isopulegol (6) is prepared from citronellal, as discussed in the section on menthol below, and is a precursor to other materials in the group. The phenols carvacrol (7) and thymol (8) are important in some herbal odour types, but the major use for thymol is as a precursor for menthol q.v. Piperitone (9) and pulegone (10) are strong minty odorants, the latter being the major component of pennyroyal oil. 1,8-Cineole (11) is the major component of such eucalyptus oils as Eucalyptus globulus. These oils are inexpensive and so there is no need to prepare cineole synthetically. Menthofuran (12) is an important minor component of mint oils and can be prepared from pulegone. 

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... 

Another complication is that most of our descriptions are of complex mixtures and individual chemical signals are not always additive in a simple predictable arithmetic way. For example, it is known that the odours of the enantiomers of carvone are different. 1-Carvone (13.2) smells of spearmint whilst d-carvone (13.3) smells of caraway. Less well known is the fact that addition of nonanol (13.4), an alcohol with an oily smell reminiscent of unperfumed washing up liquid, to 1-carvone, will create an odour impression very similar to that of d-carvone. This... 

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