Essential oils esters

Essential oils (Section 26 7) Pleasant smelling oils of plants consisting of mixtures of terpenes esters alcohols and other volatile organic substances Ester (Sections 4 1 and 20 1) Compound of the type... 

Emulsions of fatty- and petroleum-based substances, both oils and waxes, of the o/w type are made by using blends of sorbitan fatty esters and their poly(oxyethylene) derivatives. Mixtures of poly(oxyethylene(20)) sorbitan monostearate (Polysorbate 60) and sorbitan monostearate are typical examples of blends used for lotions and creams. Both sorbitan fatty acid esters and their poly(oxyethylene) derivatives are particularly advantageous in cosmetic uses because of their very low skin irritant properties. Sorbitan fatty ester emulsifiers for w/o emulsions of mineral oil are used in hair preparations of both the lotion and cream type. Poly(oxyethylene(20)) sorbitan monolaurate is useflil in shampoo formulations (see Hairpreparations). Poly(oxyethylene) sorbitan surfactants are also used for solubilization of essential oils in the preparation of colognes and after-shave lotions. 

Volatiles or Aroma. The essential oil, or aroma, of tea provides much of the pleasing flavor and scent of green and black tea beverages. Despite this, volatile components comprise only - 1% of the total mass of the tea leaves and tea infusions. Black tea aroma contains over 300 characterizing compounds, the most important of which are terpenes, terpene alcohols, lactones, ketones, esters, and spiro compounds (30). The mechanisms for the formation of these important tea compounds are not fully understood. The respective chemistries of the aroma constituents of tea have been reviewed... 

Essential oils are obtained from fmits and flowers (61,62). Volatile esters of short- and medium-chain carboxyHc acids or aromatic carboxyHc acids with short- and medium-chain alcohols are primary constituents of essential oils, eg, ethyl acetate in wines, brandy, and in fmits such as pineapple ben2yl acetate in jasmine and gardenia methyl saHcylate in oils of wintergreen and sweet birch. Most of these naturally occurring esters in essential oils have pleasant odors, and either they or their synthetic counterparts are used in the confectionery, beverage, perfume, cosmetic, and soap industries (see Oils, essential). 

Perfumes, Flavors, Cosmetics, and Soap. Many naturally occurring esters in essential oils and some synthetic esters are important fragrance and flavor compounds (61,62). They are used in perfumes, flavors, cosmetics, soaps, detergents, and air fresheners. Benzyl, butyl, ethyl, methyl, and phenyl esters of benzoic acid are used as flavors, perfumes, and food preservatives. Glyceryl 4-aminobenzoate [136-44-7] and 2-ethyUiexyl 4-dimethylaminobenzoate [21245-02-3] are used in cosmetic sunscreen preparations. Alkyl esters of 4-hydroxybenzoic acid, called parabens, have been used under various names for fungus infections of the skin, and as preservatives in lotions and creams (101). Soap and cosmetic fragrances use large amounts of amyl and benzyl saHcylate. Benzyl saHcylate [118-58-1] is also used in deodorant sprays. 2-Ethylhexyl saHcylate [118-60-5] and 2-ethylhexyl 4-methoxycinnamate [5466-77-3] are used in sunscreen formulations (102). 

These faets, however, cannot be eorreedy studied without taking into account a considerable amount of eollateral matter. For example, whilst the aetual pereentage of esters in the essential oils is inereased by the use of sodium ehloride, this salt has an inhibiting aetion on the vegetation generally, so that the aetual weight of methyl esters per acre is less than when no sodium ehloride is used, whilst the reverse is true when sodium nitrate is used. 

It will be noted that the experiments with sodium nitrate confii m the results of Charabot and Hubert, both as regards the increase in menthyl esters and the decrease in menthone in the essential oil. 

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 —... 

Hence, the acidity decreases in the course of vegetation the proportion of free linalol and the proportion of total linalol also decrease in the essence up to the time when the flowers are fully opened, whilst the proportion of ester increases then, when the flower fades, the essential oil becomes richer in linalol, whilst, on the other hand, its ester-content decreases. 

It is thus apparent that at the commencement of vegetation of the peppermint the oil is rich in menthol, hut only a small amount is present in the esterified condition. Menthone only exists in small quantity. As the green parts of the plant develope, the proportion of esterified menthol increases, as has heen found to be the case with other alcohols. This esterification, however, only takes place in the leaves, and when the essential oil extends towards the flowering tops, it becomes poorer in esters. 

Comparing the undissolved essential oil with that which was dissolved in the waters, it is seen that the former is richer in esters, poorer in free menthol and total menthol, and richer in menthone than the second. In other words the relatively sparingly soluble constituents are esters and menthone, whilst menthol is particularly soluble. 

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. 

Bodies of an alcholic nature play a very important part in both natural and synthetic perfumery. They are found to a very large extent in essential oils, both in the free state and also in the form of esters. Some that have not so far been recognised as constituents of essential oils, have been found to be so highly odorous, and so useful as perfume materials, that they are prepared artificially, and enter largely into the composition of the synthetic perfumes which to-day are indispensable to the manufacturer of perfumes. It is obvious that those alcohols which are soluble in water, such as methyl and ethyl alcohols, although they may be original constituents of some essential oils, are removed by the ordinary distillation processes, so that they do not, in fact, appear in the essential oil as found in commerce. 

This alcohol, the lowest of the paraffin series, is found in the distillation waters of a number of essential oils, being soluble in all proportions in water. It does not therefore form a constituent of essential oils in the form in which they are found in commerce. In the form of esters, methyl alcohol is found as a constituent of a number of essential oils, such as, for example, oil of wintergreen, which consists almost entirely of methyl salicylate. Methyl alcohol, CH OH, is a liquid of specific gravity 0 810, boiling at 64°. 

Normal hexyl alcohol, CH. CHj. CHj. CHo. CHj. CHjOH, is found, principally in the form of esters, in a few essential oils, especially the oil... 

Geraniol, Cj(,Hj-OH, is a constituent of many essential oils, both in the free state and in the form of esters. It is present to a very large extent in palmarosa oil, ginger-grass oil, and citronella oil, principally in the free state, and in geranium oil, to some extent in the free state, but principally in the form of esters. It is also an important constituent of otto of rose, and is present in numerous other oils belonging to the most distantly related groups. 

Linalol is found very widely distributed in essential oils. It forms the principal constituent, in the free state, of oil of linaloe, and the chief odorous constituent, in the form of esters, in bergamot and lavender oils. It is also found in ylang-ylang, rose, champaca leaf, cinnamon, petit-grain, spike, geranium, lemon, spearmint, and numerous. other essential oils. 

This alcohol, of the formula CjoHj O, occurs in the essential oil Bupleurum fi-uticomni, from which it was isolated hy Francesconi and Semagiottod It was separated hy means of its phthalic acid ester, and is an oil of faint rose odour, having the following characters —... 

Benzyl alcohol, C Hj. CHjOH, is the lowest member of the normal series of aromatic alcohols containing the benzene nucleus. It exists to a certain extent in the free state, but more often in the form of esters, principally of acetic, benzoic, and cinnamic acids, in a number of essential oils, such as those of jasmin, tuberose, cassie fiowers, and ylang-ylang. 

There is an isomeric and closely associated alcohol, phenyl-methyl carbinol, CgH5CH OH)CHg, known to chemists. This is a liquid of different odour, but which is not used very much in synthetic perfumery. It is an oil boiling at 203°, and forms an acetate which is found naturally in essential oil of gardenia. This ester is of use in blending perfumes of this type of flower. 

Cinnamic alcohol, C Hj. CH CH. CH OH, or y-phenyl-allyl alcohol, is found in the form of esters, principally of either acetic or cinnamic acid in storax, balsam of Peru, and in hyacinth and other essential oils. 

Myrtenol, CjpHjgO, is a primary cyclic alcohol, which was isolated from essential oil of myrtle, in which it occurs principally in the form of its acetic ester, by von Soden and Elze. It is separated from geraniol, with which it is found, by fractional distillation, and by the crystallisa-... 

The esters play a most important part in the economy of plant life, and are highly important constituents of numerous essential oils. Indeed, in many cases they are the dominating constituent, and the oil may be said to owe its perfume value largely, or in some cases almost entirely, to the esters it contains. 

The section on the esters, is, in the main, reproduced from a monograph by the a4ithor in the Perfumery and Essential Oil Record, July, 1913. 

Methyl alcohol, CH3OH, is the lowest member of the paraffin alcohols, and although it occurs to a small extent in the free state in a few essential oils it is not a perfume material at all, and, being very soluble in water, is entirely washed out of the oil by the distillation waters. There are, however, a number of highly odorous esters of methyl alcohol which are indispensable in synthetic perfumery. These are as follows —... 

Ethyl Benzoate.—This ester has not been found, so far, to occur naturally in essential oils. It has, however, been prepared by synthetic processes, for example, by condensing ethyl alcohol with benzoic acid by means of dry hydrochloric acid gas. Its odour is very similar to that of methyl benzoate (q.v.), but not quite so strong. It is an oil of specific gravity I OfilO, refractive index 1 5055, and boiling-point 213° at 745 mm. It is soluble in two volumes of 70 per cent, alcohol. 

Ethyl Cinnamate.—The cinnamic ester of ethyl alcohol is a natural constituent of a few essential oils, including camphor oil and storax. It is formed synthetically by condensing cinnamic acid and ethyl alcohol by dry hydrochloric acid gas. It has a soft and sweet odour, and is particularly suitable for blending in soap perfumes. It is an oil at ordinary temperatures, melting at 12°, and boiling at 271°. Its specific gravity is 1 0546, and its refractive index 1 5590. 

The esters belonging to the geraniol series of alcohols are absolutely indispensable in the manufacture of artificial perfumes. When it is remembered that these esters are present in such oils as bergamot, rose, geranium, lavender, petit-grain, neroli, and numerous other sweetsmelling essential oils, it will readily be seen how useful they are in building up similar perfumes artificially. 

---