Eucalyptus citriodora

In many natural products citronellol occurs as a mixture of its two enantiomers the pure (+) or (-) form is seldom found. (+)-Citronellol dominates in oils from Boronia citriodora (total citronellol content ca. 80%) and Eucalyptus citriodora (citronellol content 15-20%). (-)-Citronellol is the predominant enantiomer in geranium and rose oils, both of which may contain up to 50% citronellols. 

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. 

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. 

Eucalyptus citriodora oil is obtained by steam distillation of leaves and terminal branches of Eucalyptus citriodora Hook. It is an almost colorless, pale yellow, or greenish-yellow liquid with a citronellal-like odor. 

The major producer is Brazil with over 500t/yr, but considerable quantities are also produced in other countries (e.g., South Africa and India). Eucalyptus citriodora oil is a starting material for the manufacture of citronellal and products derived from it. It is also used in perfumery for the same purposes as citronellal. FCT 1988 (26) p.323 [85203-56-1]. 

N.A. Eucalyptus citriodora Hool. E. globulus Labill. Cineole, eucalyptol, caffeic acid, coumaric acid, gallic acid, gentisic acid, hydroxybenzoic acid, syringic acid, vanillic acid.99-100 Externally for athlete s foot, dandruff, herpes, and an inhalation for fevers and asthma. 

Achillea millefolium, Alpinia galanga, Artemisia vulgaris, Crocus sativus, Eucalyptus citriodora,... 

Coumaric acid Eucalyptus citriodora, E. globulus, Populus alba... 

Gentiana lutea, G. macrophylla, G. scabra Gentiana lutea, G. macrophylla, G. scabra Centaurium erythraea Eucalyptus citriodora, E. globulus... 

Ananas comosus, Eucalyptus citriodora, E. globulus, Matteuccia struthiopteris, Phragmites australis, Spiraea ulmaria, Styrax benzoin, Tilia cordata, T europaea Centella asiatica... 

Eucalyptus (lemon-scented) Eucalyptus citriodora (Myrtaceae) fresh leaves... 

Eucalyptus citriodora has a strong antimicrobial activity, but tests on individual components showed relative inactivity. However, when combinations of the three major components in the same ratios occurring in the natural oil were mixed and used, antimicrobial activity was restored. 

The main essential oil-producing species of Eucalyptus include Eucalyptus globulus, also called blue gum eucalyptus Eucalyptus dives, known as broadleaved peppermint eucalyptus Eucalyptus citriodora, known as lemon-scented eucalyptus Eucalyptus radiata, known as narrow-leaved peppermint gum Eucalyptus smithii, known as gully gum and Eucalyptus polybractea, known as blue mallee. Within each species there are many subspecies and chemo-types. This illustrates a very complex situation, producing essential oils with varying compositions and properties. 

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... 

Figure 7.12 Eucalyptus. Analysis of Eucalyptus citriodora, showing a typical composition with a high level of citronellal (73.94°/o). Courtesy of Jenny Warden, Traceability.

H. Nishimura J. Mizutani, Identification of Allelochemicals in Eucalyptus citriodora and Polygonum sachalinense. In Allelopathy Organisms, Processes, and Applications, Inderjit, K. M. M. Dakishini, F. A. Einhellig, Eds. American Chemical Society Washington, DC, 1995 pp 74-85. 

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). 

Eucalyptus citriodora Hook f. Leaves F 2.2-8.3 citronellal, citronellol, isopulegol, 1,8- 68,69... 

Derivation From citronellal (Java citronella or Eucalyptus citriodora). 

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. 

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