Oil of geranium

The progressive development of the geraniol compounds in essential oils has been principally studied in the case of oil of geranium. 

It will be seen that (1) the acidity decreases during the maturing of the plant (2) as in all the cases previously considered, oil of geranium becomes ricber in esters during vegetation (3) tbe proportion of total alcohol increases slightly and the quantity of free alcohol decreases, but not to an extent corresponding with the increase of esters, so that in the course of esterification, which takes place in this case without dehydration, a small quantity of alcohol is produced. 

There seems, however, to-day, to be overwhelming evidence that the French chemists were correct and that citronellol and rhodinol are two very similar, but chemically different, compounds, citronellol being represented by the formula (1) and rhodinol by formula (2). Considerable evidence of this is to be found in the work of Barbier and Locquin. Starting from the acetic esters of ordinary d-citronellol and rhodinol from oil of geranium or rose, they attached hydrogen chloride to the double bond, and obtained the same additive product according to the equations — ... 

Examples of monoterpenes include the linear aldehyde citral, which is found in many essential oils, and the (cis) alcohol geraniol, a major component of oil of geranium. Cyclic monoterpenes include limonene, menthol, pinene, camphor, and carvone, major components of lemon oil, mint oil, turpentine, camphor oil, and caraway oil, respectively. Sesquiterpenes include farnesol, a component of rose oil, and bisabolene, a component of Bisabol myrrh. The diterpenes include phytol, a component of chlorophyll, and vita-... 

Olefine Terpenes.— The olefine terpenes and the alcohols and aldehydes derived from them are found in several essential oils, e.g.y oil of geranium contains geraniol and citronellol (p. 167), and oil of lemony citral and citronellal (p. 170). 

Well-known eudesmane derivatives in flavors and fragrances include a- and p-selinene from the oils of Cannabis saliva var. indica (Moraceae), celery (Apium graeveolens, Umbelliferae) and hops (Humulus lupulus, Moraceae), (+)-a- and (+)-P-eudesmol from some oils of eucalyptus (Eucalyplus macarlhuri), (-)-epi-y-eudesmol with its woody odor from the north African oil of geranium (Pelargonium odoralissimum and allied species), and the almost odorless diastereomeric (+)-y-eudesmol from various ethereal oils (+)-p-Costus acid and (+)-p-costol belong to the constituents of the essential oil obtained from the roots of Saussurea... 

The strikingly different odors of cis-trorw-isomers and diastereomers is demonstrated by various other pairs of terpenes. For example, the synthetie fragranee (E)-S-methyl-a-ionone has a lovely flowery smell like the blossoms of violets, whereas the (Z)-isomer emits a woody tobaceo-like odor. Likewise, the strongly woody smelling sesquiterpene (-)- /-y-eudesmol from Algerian oil of geranium eontrasts wifli the almost odorless diastereomer (-l-)-y-eudesmol whieh is wide-spread among ethereal oils. 

Geraniol, as Its name Implies, occurs in oil of geranium but also constitutes about 50% of rose oil, the extract of rose petals. Farnesol, which occurs In the essential oils of rose and cyclamen, has a pleasing lily-of-the-valley odor. Both geraniol and farnesol are used in making perfumes. 

ISO/DIS 4731, 2005. Oil of Geranium. Geneva, Switzerland International Standard Organisation. 

The relative proportions of the two alcohols, geraniol and dtronellol, in oil of geranium oil is a matter of considerable interest, and the determination is frequently of importance. The only method available in practice for this purpose is the combination of the acetylation process, which gives the measure of the total alcohols and the formylation process, by which the geraniol is decomposed, and the citronellol estimated. 

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