Essential oils citronellal

Synthesis of (+)- and ( )-Citronellol from the Citronellal Fraction of Essential Oils. (+)-Citronellal is obtained by distillation of Java citronella oil and is hydrogenated to (+)-citronellol in the presence of a catalyst (e.g., Raney nickel). Similarly, (zb)-citronellol is prepared from the ( )-citronellal fraction of Eucalyptus citriodora oil. 

Isolation from Essential Oils. (+)-Citronellal is obtained from citronella oils by fractional distillation. ( )-Citronellal is isolated from Eucalyptus citriodora oil when necessary, it is purified by using an addition compound, e.g., the bisulfite derivative. 

Synthesis from Citronellal. Citronellal can be hydrogenated to citronellol by the use of special catalysts and/or special hydrogenation techniques, e.g. [47]. The citronellal which is used as starting material may originate from synthetic production or from isolation of essential oils. Citronellal from citronella oil yields (+(-citronellol the corresponding material from citronellal from Eucalyptus citriodora oil is racemic. Pure (+(-citronellol is also obtained from (+)-citronellal which is produced as an intermediate of (-(-menthol (see p. 55-58). By this asymmetric technology, pure (-(-citronellal and therefore pure (-(-citronellol is also available. 

Thujone was discovered by E. Schweizer. C. VolckeP discovered carvone in carraway seed oil, and cineol in wormseed oil. Carvone was shown to be a ketone related to limonene by H. Goldschmidt and R. Ziirrer. Linalool was discovered by distilling coriander oil by A. Kawalier and prepared from linaloe wood (licari kamali) by H. Morin.Geraniol was discovered by O. Jacobson in oil of palma rosa. F. W. Semmler " showed that it is an olefinic terpene with an open carbon chain. Menthone was obtained from oil of peppermint by R. W. Atkinson and H. Yoshida. (Menthol was known much earlier and was analysed by Dumas in 1832.) G. Bouchardat and R. Voiry obtained terpineol from essential oils. Citronellal (an aldehyde) was discovered by F. D. Dodge.2 ... 

Isopulegol, Cj Hj O, does not appear to exist in essential oils, but it results from the action of acids on citronellal. The last-named body, for example, when boiled with acetic anhydride yields isopulegyl acetate, from which the alcohol is obtained by hydrolysis. 

Citronellal which was originally termed citronellone, is one of the characteristic constituents of citronella oil, in which it occurs to a considerable extent. It can be prepared by shaking the essential oil with a hot solution of sodium bisulphite, and decomposing the resulting bisulphite compound by means of sodium carbonate and distilling the citronellal in a current of steam. Citronellal is optically active, and it is probable that the specimens isolated from natural sources are mixtures of the two optically active isomers, so that the actual theoretical rotation is not known with certainty. 

Citronellic acid, C Hj-. COOH, is the acid corresponding to the alcohol citronellol, and is present in the essential oil of Barosma jmlcliel-lum. It has the following characters —... 

Among the acyclic terpene aldehydes, citral and citronellal hold key positions as fragrance and flavor chemicals, as well as starting materials for the synthesis of other terpenoids. Hydroxydihydrocitronellal is one of the most important fragrance materials. Derivatives of these aldehydes, particularly the lower acetals, are also used as fragrance materials. Acyclic sesquiterpene aldehydes are not very important as such, but they contribute to the characteristic fragrance and aroma of essential oils, for example, in the case of a- and /3-sinensal in sweet orange oil. 

Id 13.1°, occurs in essential oils in its (+) and (-) forms, often together with the racemate. (+)-Citronellal [2385-77-5] occurs in citronella oil at a concentration... 

Production. Citronellal is still isolated from essential oils in considerable quantities it is also produced synthetically. 

Although a small amount of acyclic terpene acids such as geranic acid and citronel-lic acid occurs in many essential oils, often as esters, they are rarely used in perfume and flavor compositions. Methyl geranate is an intermediate in a-damascone synthesis and is sometimes needed in the reconstitution of essential oils. 

The isopulegols occur in a large number of essential oils, often in optically active or partly racemic form. Since citronellal readily cyclizes to isopulegol, the latter occurs frequently in citronellal-containing essential oils, in which it is formed during the recovery of the oil. 

Individual compounds can be isolated from essential oils containing one or only a few major components by distillation or crystallization. Examples are eugenol from clove oil, menthol from commint oil, citronellal from Eucalyptus citriodora oil and citral from Litsea cubeba oil. These compounds are used as such or serve as starting materials for the synthesis of derivatives, which are also used as flavor and fragrance substances. However, the importance of some of these oils has decreased substantially because of the development of selective synthetic processes for their components. 

Many of the monoterpenes found in essential oils of plants also occur as pheromonal substances in insects (45,57-60) and are often involved in plant-insect interactions. Some compounds found both in plants and insects are the monoterpenes citronellal, cit-ronellol, geraniol, myrcene, citral, 6-phellandrene, limonene, 2-terpinolene, a-pinene, 6-pinene, 1,8-cineole, and verbenone. 

The determination of aldehydes and ketones is of importance in the analysis of those essential oils characterised especially by aldehydic or ketoruc principles, e g.,the citral contained in lemon and lemongrass oils, citronellal in citronella Oil and some eucalyptus oils, benzaldehyde in bitter almond oil, salicylaldehyde in meadow-sweet oil, anisaldehyde in aniseed and fennel oils, cuminaldehyde m cumin oil, cinnamaldehyde in cinnamon oil, carvone in caraway oil, pulegone in pennyroyal oil and methyl nonyl ketone in rue oil The determination of the aldehydes and ketones presents, however, difficulties and the above methods are moderately exact in only a few cases, especially when the content of aldehydes or ketones is considerable The bisulphite method is applicable particularly to the determination of cinnamaldehyde and benzaldehyde in cinnamon oil and bitter almond oil, and, up to a certain pomt, to that of citral in lemongrass Oil. The sulphite method gives good results in the same cases and for the determination of carvone and pulegone... 

With fractional distillation, single aroma chemicals can also be obtained, in more or less highly purified form, from essential oils. These are designated as isolates. In the days when synthetic organic chemistry was less versatile and powerful than it is today, this was the only way to obtain many aroma chemicals. Even today it is in some cases, such as citronellal or cedrol, the most economical way. 

Citronellal (3,7-dimethyl-6-octenal) Found in essential oils of citronella, eucalyptus citrioda and melissa. Citrus, strong smell very characteristic of citronella. (Fig. 3.8)... 

The GC analysis shows samples of Eucalyptus citriodora (Fig 7.12) and Eucalyptus radiata (Fig 7.13). Both of these traces show that published data are not always found in actual samples of essential oil. The Eucalyptus citriodora shows a high level of citronellal (73.94%), while the Eucalyptus radiata has a high level of 1,8-cineole (76.37%) both of these are higher than in the published data. However, for Eucalyptus radiata values of 1,8-cineole... 

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). 

Eucalyptus citriodora Hook f (Lemon gum) The oil of the fresh leaves of E. citriodora (2.2-8.3%), a tree introduced into Kenya from Australia (68), has been well researched in Kenya. Results indicate that there are two chemical varieties that were introduced. The chief essential oil constituents of one variety are citronellal (65-88%), citronellol (2-25%) and isopulegol (2-19%). In constrast, the second variety has as its major essential oil consitutents citronellol (32-52%), citronellal (38-59%) and 1,8-cineole (2-19%) (68,69). The essential oil is regarded as a perfumery oil. This plant is the second most commercially important Eucalyptus species in the essential oil trade and is only second to E. smithii Baker (69). The aromatic oil is used in soaps, creams and lotions due to its desirable odor properties, and as with many other essential oils is also used extensively in many technical preparations to mask other industrial malodors. A highly active mosquito repellent compound, p-menthane 3,8-diol has been isolated from the waste water of distillation of E. citriodora. There are now many commercial mosquito repellents based on this waste water (70-73). 

C12H22O2, Mr 198.30, hpioi.3 kPa 240 °C, cf° 0.8901, rv 1.4515, occurs in many essential oils either as one of its optical isomers or as the racemate. The odor of racemic citronellyl acetate differs little from that of the optical isomers. ( )-Citronel-lyl acetate is a liquid with a fresh-fruity rose odor. It is often used as a fragrance, for example, for rose, lavender, and geranium notes as well as for eau de cologne with citrus nuances. Since it is relatively stable to alkali, it can be used in soaps and detergents. Citrus flavors acquire specific character through the addition of citronellyl acetate it is also used to round off other fruit flavors. 

Good-quality drugs should yield up to 0.2% essential oil with 30%-40% citronellal and 20%-30% citral (sec Fig. 14, track 2). In lower-quality oils, such as sample I, the amount of terpene alcohols dominate. 

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