Essential oils Examination

The differences in composition between the two essential oils examined show well, if they be compared with those which exist between the essential oils of the leaves and the inflorescences, that the distribution of the odorous principles between the leaf, the organ of production, and the flower, the organ of consumption, tends to take place according to their relative solubilities. But this tendency may be inhibited, or on the other hand, it may be favoured by the chemical metamorphoses which the substances undergo at any particular point of their passage or at any particular centre of accumulation. Thus, in the present case, some of the least soluble principles, the esters of menthol, are most abundant in the oil of the leaves, whilst another, menthone, is richest in the oil of an organ to which there go, by circulation, nevertheless, the most soluble portions. This is because this organ (the flower) constitutes the. medium in which the formation of this insoluble principle is particularly active. 

The published data relating to the composition of a particular oil can vary owing to factors already outlined. It will also vary with the source of information and for each oil studied there may be different compounds and values quoted. Even the accepted ranges quoted for the same compound will vary from source to source. This chapter will show this in the individual essential oils examined, and draws information and data from a variety of sources. 

The modified Ir data for monoterpene hydrocarbons from the three species of citrus oils were subjected to a multivariate analysis. According to principal component (PC) analysis, the citrus essential oils examined were clearly discriminated, with 93.3% of the accumulation contribution ratio of both PCI and PC2 (Fig. 4A). As shown in Fig. 4B, p-pinene (PCI, 0.530 PC2, -0.80), a-terpinene (0.685 0.062) and P-phellandrene (0.324 0.810) were large for the absolute value of the eigenvector of monoterpene system hydrocarbons, followed by terpinolene (0.367 -0.010). These compounds greatly contributed to the modified Ir discrimination of the citrus essential oils. 

The function of the essential oil in the plant is not fully understood. Microscopic examination of plant parts that contain the oil sacs readily shows their presence. The odors of flowers are said to act as attractants for insects involved in pollination and thus may aid in preservation and natural selection. Essential oils are almost always bacteriostats and often bacteriocides. Many components of essential oils are chemically active and thus could participate readily in metaboHc reactions. They are sources of plant metaboHc energy, although some chemists have referred to them as waste products of plant metaboHsm. Exudates, which contain essential oils, eg, balsams and resins, act as protective seals against disease or parasites, prevent loss of sap, and are formed readily when the tree tmnks are damaged. 

Pickles aud Karl have made an examination of the essential oil distilled from the fruit of this plant which is alari known as An /mum mcilivm. They find that the oil resides almost entirely in the seeds. By distilling the fruits with steam, aliout 1 per cent, of a pale yellow oil, having an odour cecalliug those of lemon aud eucalyptus, was obtained. The Oil has the following chanteters —... 

The fresh herb, [ lvi-kf a ioeudo.. which is common in the sonthern parts of the United States, xheldi 0-02i per cent, of an essential oil, which has het-n examined by Hahak and found to have the f. ... 

Scalione baa examined the essential oil of Ouineria occiderUahs, or Caiycaalhut ocridealalii. which he obtained to the extent of 0 27 per cent, of the leaves and twigs. The oil bad the following characters —... 

The essential oils from the following two species of Cisias have been examined by Sehimmel Go. — ... 

From the practical point of view, the principal variation of environment which is definitely under the control of the cultivator, is, of course, the alteration in the composition of the soil, which is brought about by scientific manuring, llie analysis of fruits and vegetables will give the ordinary agriculturist much information as to the necessary mineral ingredients to be added to the soil but in the case of essential oils, the conditions are entirely different. The various parts of the plant tissue are affected in different ways by the same mineral salts, and successful development of the fruit or any other given part of the plant may have little or no relationship with the quantity or quality of essential oil produced. So that it is only by actual distillations of the plant, or portion of the plant, coupled with an exhaustive examination of the essential oil, that informative results can be obtained. 

In the case of sweet basil, Ocimwn basilicum, Charabot and Hubert have examined the essential oils distilled from plants which had been cultivated in full light and from those kept shaded from the light. Jn the former case the oil contained 57 3 per cent, of estragol and 42 7 per cent, of terpene compounds, whilst in the case of the shaded plants the estragol had risen tO 74 2per cent, and the terpene compounds fell to 25 8 per cent. 

Linalol is a tertiary alcohol of the formula Cj HjgO, which, with its acetic ester (and traces of other esters) forms the basis of the perfume,of bergamot and lavender oils. By dehydration linalol is converted into terpenes of which the principal are limonene and dipentene, and by esterification into its acetic ester. The examination of the essential oil at different periods of the development of the bergamot fruit has led Charabot and Laloue to the following conclusions. As the fruit matures the essential oil undergoes the following modifications —... 

The last of these investigations to which reference will be made is that of the peppermint, as representing the menthol group of compounds. Four samples of essential oil were examined —... 

Selinene is a bicyclic sesquiterpene occurring in essential oil of celery. Its presence was first indicated by Ciamician and Silber who announced the isolation of a sesquiterpene boiling at 262° to 269°, but no characteristic derivatives were prepared. Schimmel Co. examined this sesquiterpene to which they assigned the name selinene. They prepared a solid dihydrochloride melting at 72° to 74° and ha-ving a specific rotation -h 18°. The pure sesquiterpene, regenerated from the dihydrochloride by means of sodium ethylate had the following characters —... 

C,4H2204, melting at 182 5. The formation of this cedrene-dicarboxylic acid serves for the detection of cedrene in essential oils. It is sufficient if the fraction to be examined be oxidised by permanganate or ozone, and the acid obtained (boiling-point at 10 mm. = 200° to 220° C.) be then oxidised further, either by an alkaline solution of bromine or by nitric acid. Even very small proportions of cedrene have definitely led to the obtaining of this acid melting at 182 5° C. 

Perillic aldehyde, Cj Hj O, is present in the essential oil of Perilla nankinensis. It has been examined by Semmler and Zaar, who isolated it from the oil by means of its sodium sulphite compound. Perillic aldehyde has the following characters —... 

The hitherto unanswered question whether the chemically identical thujonas isolated from various essential oils are also physically identical, or whether they are physically isomeric, has now been decided by Wallach in the last-named sense. He has succeeded in establishing the presence of two and possibly of three thujones, although with regard to the third the more probable view is, that it represents a mixture of the other two. His examination has, moreover, proved that thuja oil contains essentially... 

The author and several other chemists have for some years past persistently advocated the use of the refractometer in the examination of essential oils. Although this determination was regarded as of little use by many chemists, it is now generally recognised that it is indispensable. But its value is only to be properly estimated by a very careful consideration of the results obtained. 

The value of fractional distillation in the examination of essential oils cannot be overestimated. The various fractions may be examined and their specific gravities, optical rotations, and refractive indices determined. The combination of these figures will often give the experienced analyst the most useful information and save him many hours needless work. Experience alone, however, will teach the chemist to make the fullest use of the results so obtained. In most cases distillation under reduced pressure is necessary on account of the risk of decomposing the various constituents of the oil. The use of a Briihl receiver (or any similar contrivance), which is easily obtained from any apparatus maker. 

Benedikt and Grussner have proposed the determination of the methyl number in the analysis of essential oils. Whilst this process may have some vaAue in the examination of the constitution of a compound, it is very rarely necessary to use it in the analysis of essential oils. The methyl number (which is a somewhat fallacious term as it includes other Alkyl radicles) is understood as the number of miUigrams of methyl yielded by the gram of the substance when heated with hydriodic acid. From 0 2 to 0 3 gram of the oil is heated with hydriodic acid of specific. gravity 1 7 and the methyl iodide formed collected in a suitable receiver,... 

Returning to the terpenes for a moment, it is interesting to note that Perry et al. (1997b) also examined the essential oils of Kunzea ericoides (A. Rich.) J. Thompson... 

As part of a study of the secondary chemistry of members of Cistus (the rock-rose) in France, Robles and Garzino (1998) examined the essential oil of C albidus L. Plants were sampled from two areas in Provence characterized by different soil types, calcareous sites west of Marseille, and siliceous sites near Pierrefeu-du-Var and Bormes les Mimosas (PF and BM, respectively, in Fig. 2.23), which lie about 60 km and 80 km to the east, respectively, in the Massif les Maures. Regardless of the soil type, a-zingiberene [88] (Fig. 2.24) was the dominant component. Concentrations of other major components of the plants varied between the two soil types, as summarized in Table 2.6. Many other compounds were present in lesser amounts, but varied little between the two areas. A more recent paper by the same workers (Robles and Garzino, 2000) described an analysis of C. monspeliensis L. leaf oils, the results of which are summarized in Table 2.7. 

Studies of the essential oils of Thymus species have documented the existence of several chemotypes with greater or lesser geographical distinctions among them. In an examination of the essential oils of T. vulgaris L. native to France, Granger and Passet (1973) described six chemical phenotypes based upon the occurrence of a number... 

The percentage of essential oil content in dry chamomile flower-heads and its qttali-tative and qrrantitative characteristics, which were determined by the GC-analysis are presented in comprehensive Table 7.1. Percentage corrterrts of the essential oil from chamomile flower anthodia were ranging 0.63 0.19 over the whole examined samples. 

The use of enantiomers as additional markers for taxonomic characterization of aromatic plants may be very helpful. The differences in the enantiomeric distribution of trans- and cis- sabinene hydrates in two Origanum species enable the species to be distinguished in spite of their similar essential oil compositions. A further study on the natural variation of the enantiomeric composition within a wild population may be carried out in order to examine the stability in a taxon (including the possible presence of chemotypes). The enantiomeric ratio of essential oil components is a reliable parameter for assessing quality because it may be indicative of adulteration, contamination, aging, shelf life, technological process and the botanical source of a specific chiral compound. ... 

G.l.c. papers of interest include the classification of 22 acyclic monoterpenoid alcohols according to retention indexes, resolution of cyclic ketones [e.g. ( )-menthone, ( )-isomenthone] as diethyl (+)-tartrate acetals, and the use of lanthanide shift reagents to resolve non-terpenoid racemic epoxides.The occurrence and prevention of monoterpenoid hydrocarbon isomerization during silica gel chromatography has been examined and the separation of monoterpenoids and sesquiterpenoids by gel permeation chromatography is reported. Monoterpenoid hydrocarbons have been selectively extracted from essential oils using dimethylsilicone. ... 

BERGAMOT OIL. An essential oil, Brownish-yellow to green liquid, agreeable odor, bitter taste, produced from the nnd of the fruit of Citrus aurantium or C. bergamia, relatives of the orange and lemon, The small trees are cultivated in southern Europe. The oil is expressed from the skin of the small yellow fruits and sometimes is used as a scent for cosmetics. The oil also is used sometimes as a clearing agent in the preparation of material for microscopic examination. 

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