Dextro-Carvone

Often the difference in odor between two such forms is surprisingly great. For example, dextro carvone is the main odor constituent of caraway oil, while its optical isomer levo carvone is typical of spearmint. Among other materials that occur in important dextro and levo forms are citronellol and rose oxide. 

Carvone, CjjHj40, is the ketone characteristic of dill and caraway oils. It occurs in the dextro-rotatory form in these oils, and as laevo-carvone in kuromoji oil. 

G. Vavon has examined the hydrogenation of carvone, in presenc of platinum black as a catalyst, and shown that it takes place in three entirely distinct phases. Carvone fixes successively three molecules of hydrogen, giving dextro-carvotanacetone, then tetrahydrocarvone, and finally carvomenthol. 

Carvone In the dextro (d) form carvone is found in caraway and dill essential oils. In the laevo (l) form it is the main constituent of spearmint oil (Fig. 3.9). 

Derivatives of Menthene.— The most important alcohols and ketones derived from the menthene unsaturated group of terpenes are terpineol, di-hydro carveol, di-hydro carvone and pulegone. The first one, the alcohol terpineol, occurs in its dextro form in cardamon oil and marjoram oil, in its leoo form in neroU oil and in its inactive form in cajeput oil. The constitution is proven by Perkin s synthesis from As-tetra-hydro para-toluic acid by means of the Grignard reaction. 

As an example of the co-existence of systematic, semi-systematic and trivial names, we could look at the monoterpenoid ketone, carvone. Carvone occurs in both enantiomeric forms in nature, the laevo-form in spearmint and the dextro-form in caraway. The trivial name carvone is derived from the Latin name for caraway, Carum carvi. The basic carbon skeleton is that of l-isopropyl-4-methylcyclohexane. This skeleton is very common in nature and is particularly important in the genus Mentha, which includes various types of mint, since it forms the backbone of most of the important components of mint oils. The skeleton has therefore been given the name p-menthane and the numbering system used for it is shown in Figure 1.3. Therefore, any of the following names may be used to describe the same molecule carvone, p-mentha-1,8-dien-6-one and 1 -methyl-4-(l-methylethenyl)cyclohex-l-ene-6-one. To classify it, we could say it was an unsaturated ketone of the /7-menthane family of monoterpenoids. 

The leaves and young twigs of Lindera sericea, one of the Japanese Lomraoem, yield the oil own in commerce under this name. It is a dark yellow oil with a strong aromatic and balsamic odour, of specific gravity from SQO to 915, usually about 900, and faintly laevo-rotary. It has been examined by Ewasnij who states that it contains dextro-limonene, di ntene, inactive terpineol, and laevo-carvone. The oil, on account of its comparatively low price, has recently come into some favour as an aromatic. 

Naturally occurring carvone, existing as two optical isomers dextro- and /cvo-enantiomer), is a member of the terpenoid family, which is fotmd in many essential oils. 

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