Esters linalyl acetate

The essential oil is a pale yellow with a light, bitter-sweet floral odour. The absolute is darker and more viscous with an odour closer to the original flower. The main chemical components of the essential oil are the alcohol lin-alool (30-37%), the ester linalyl acetate (6-17%) and monoterpenes limonene (12-18%) and [3-pinene (12-15%). Also present geraniol (2-3%), nerol (1-3%), nerolidol (3-6%), citral and jasmone. Both the plant and the essential oil have many established uses. The essential oil is considered to be one of the most effective as a sedative, carmative and antidepressant and often used to treat insomnia. It is also claimed to be relaxant for smooth muscle (internal, involuntary muscles) especially those of the gut. Suitable for all skin types, both the essential oil and hydrolat are versatile materials for the aromatherapist. Considered safe as it is nonirritant and non-sensitizing and an example of a non-phototoxic citrus essential oil. 

Most esters are formed by reaction of terpene alcohols with acetic acid. They are among the most widespread volatile oil compounds— being found mainly in flowers— however, they are generally present in small amounts. Their distinctively fragrant aromas characterise many of the oils in which they appear. Lavender oil contains the alcohol linalool along with its ester linalyl acetate the relative abundance of these two constiments is considered to be an indicator of high quality. 

The species-speci c behavior in these biogenetic transformations is demonstrated by the fact that the related species Mentha citrata (syn. M. piperita var. citratd) shows an opposite tendency as the compound linalool increases by approximately 30% during owering, while the corresponding ester, linalyl acetate, is decreasing at the same time (Malizia et al., 1996). 

Due to its pleasant odor, (-)-linalyl acetate is used as ingredient in perfumes and cosmetic products. It is a major compound in the essential oils of petitgrain (Citrus aurantium spp. auran-tiurri), Citrus bergamia and L. angustifolia (Bornscheuer et al., 2014 O Neil, 2006). As an ester, linalyl acetate is hydrolyzed in vivo by carboxylesterases or esterases to linalool (Figure 9.17), which is then further metabolized to numerous oxidized products (see metabolism of linalool) (Bickers et ah, 2003). 

The volatile oil (bitter orange oil) contains more than 90% monoterpenes (main f-limonene, also myrcene, campherr pinene, ocimene, p-cymene, etc.) small amounts of alcohols (linalool, terpinene nerol, farnesol, nerolidol, octanol, etc. usually 0.5-1% aldehydes (mainly decanal also nonanal, dodecanal, citronellal, neral acetaldehyde, formaldehyde, etc.), and ketones (carvone, a-ionone, and jasmine) free acids (octadeca-dienoic, pelargonic, cinnamic, acetic, etc.) about 2.4% esters (linalyl acetate, decyl pe-largonate, octyl acetate, geranyl acetate, etc.) coumarins (osthole and auraptenol) and others (jiangsu list and horhammer). 

Aroma chemicals are isolates, or chemically treated oils or components of oils. Some components are removed physically, others chemically. In most cases, they are further purified by distillation. For example, Bois de Rose (rosewood) oil may be distilled to isolate linalool, which may be then further treated chemically to yield derivatives such as linalyl acetate, an important fragrance ingredient and a primary component in its own right of lavender and lavandin oils. Vetiver oil Haiti, although containing only 70% alcohols, is treated with acetic anhydride, then carefully distilled to include valuable odor components in the distillate, even though they may not be esters. 

Generally speaking, lavandin oil is characterized by a lower quantity of esters, the most critical of which for odor quaUty is linalyl acetate (24). The French specification organization (AFNOR) has fixed provisional standards for both oils (17) (Table 6). 

The fact that the amount of total linalol decreases whilst the richness in linalyl acetate increases, proves that linalol appears in the plant at an earlier period than its acetic ester. Further, the free acetic acid acting on the linalol esterifies a portion of it, whilst another portion of this terpene alcohol is dehydrated, with the production of limonene and. dipentene, which are the usual resultants of linalol in presence of certain dehydrating agents. This view is corroborated by the fact that the quantity of the mixed terpenes increases during the esterification, without the slightest variation being observed in the ratio between the... 

Esters, or salts of alkyl radicles, such as linalyl acetate, etc., are frequently the most important constituents of essential oils. Their importance is especially noteworthy in such cases as lavender , bergamot, peppermint, and wintergreen oils, and their estimation is very frequently necessary. The principle upon which this depends is the fact that most esters are decomposed by solution of caustic alkali (preferably in alcohol) according to the equation—... 

As the free acids present in essential oils consist in the main of acetic acid, they are, when necessary, calculated in terms of acetic acid in the same way the esters are conventionally calculated from the alkali required for their hydrolysis, in terms of the principal ester present, for example, linalyl acetate in the case of lavender and bergamot oUs, and geranyl tiglate in the case of geranium oil. 

Terpinyl acetate in the absence of esters of high molecular weight, or ethyl esters of the fatty acids of coconut oil, is indicated by a difference to be observed in the apparent ester value by different times of saponification. This ester is far more resistant to the action of caustic alkali than is linalyl acetate, and requires two hours at least for complete saponification. Hence, if the oil shows a difference in the saponification value in thirty minutes and in two hours, which amounts to more than from 1 to 2, terpinyl acetate is almost certainly present. The following table shows the effect of this partial-saponrfication on the two esters and on adulterated oils —... 

Linalool, 3 231, 232, 233 24 477, 495, 496, 500-503, 546 acid treatment of, 24 502 epoxidation of, 24 502 main producers of, 24 501 Linalool oxide, 24 502 Linalyl, 24 479 Linalyl acetate, 24 501 Linalyl alcohol, 24 500 Linalyl esters, 3 231 Linalyl oxide, 24 503 Lincomycin, registered for use in aquaculture in Japan, 3 221t Lincosamide, bacterial resistance mechanisms, 3 32t Lindane, 13 145-147... 

Because the lower fatty acid esters of geraniol, linalool, and citronellol are important contributors to the odor of many essential oils, these esters are widely used in the reconstitution of such oils, as well as in perfume and flavor compositions. The acetates, particularly linalyl acetate, are most widely used. The use of formates is limited by their relative instability. Higher esters are not important in terms of quantity, but are indispensable for creating specific nuances. 

Among the linalyl esters, the acetate is by far the most important fragrance and flavor substance. The formate, propionate, and butyrates are used in small amounts. 

Methyl salicylate 144 (Structure 4.44), the main constituent of wintergreen oil, is derived from benzoic acid. Other important esters are linalyl acetate 145, benzyl benzoate 146 and benzyl isobutyrate 147. 

Alteration of essential-oil components during distillation can be recognized by comparing the oils obtained by steam distillation and by SFE. The hydrolysis of esters (like linalyl acetate) to the corresponding alcohols was observed in clary sage oils. The hydrolysis of thymol bound in glycosides resulted in different thymol concentrations in distilled thyme oils, which was proved by appropriate treatments (acidic and enzymatic) of the previously CO2-extracted plant material. 

The ester number for any essential oil may vary within more or less wide limits (see Table XXXIV), but its determination is of importance in the identification of an oil, the detection of adulteration, and for judging of the quality of the oil. With some oils, the esters represent the odoriferous principle, e.g., linalyl acetate in bergamot, lavender and petit-grain oils, bomyl acetate in pine-needle oil and menthyl acetate in mint oil, the value of these Oils being deduced from the ester content. 

Of this residue, dissolved in a little neutral alcohol, the acid and ester numbers are determined, these being due to resinous, fatty and waxy substances naturally present in the bergamot oil. The ester number is converted into the corresponding percentage (n) of linalyl acetate (see paragraph 2) and the quantity of this ester contained in the percentage ( -) of residue left by the oil then calculated from the formula, (n x r)/ioo. This amount of linalyl acetate is subtracted from that found in the oil, as in paragraph . 

Detection of Terpinyl Acetate (SchimmeVs method).—The saponification of the linalyl acetate of bergamot oil is complete after 15-30 minutes boiling with N/2-alcoholic potash, but with terpinyl acetate at least an hour is necessary for complete saponification. The latter ester may thus be detected by carrying out two distinct saponifications, one for 30 minutes... 

A bergamot oil which does not correspond with the more important of the above specific characters for the genuine oil is to be regarded as adulterated. This is the case, for instance, with an oil having D below o-88o or above 0-887 or ci below + 70 or above + 250, or containing less than 33% or more than 45% °f esters (as linalyl acetate), or not dissolving completely in half its volume of cfo% alcohol. 

The residue on evaporation Of the genuine oil is 5-6% and its ester number 138-180, corresponding with 47-6-63% of linalyl acetate the 5-6 grams of residue are thus equivalent to about 2VJ-3-8 grams of linalyl acetate. Oil of lemon, terpenes, rectified bergamot oil or mineral oils diminish the residue... 

Ethyl acetate, which is a comparatively small molecule, has the typical fruity character associated with all the lower esters, and a more or less equal balance between the influence of the two structural units, derived from ethyl alcohol and acetic acid. Linalyl acetate and geranyl acetate, however, although retaining the typical character of an acetate have much less of the ester fruitiness and are more closely related to the corresponding alcohols, linalool, and geraniol. The dominance of the alcohol appears to be even greater in phenylethyl acetate and paracresyl acetate (a phenolic ester). 

Esters, as has already been seen, are formed by the combination of alcohols and acids with the elimination of water. The reverse reaction, which is one of hydrolysis, can also occur under certain conditions, such as the presence of acid or alkali in an aqueous base. Not all esters are equally susceptible to this type of breakdown, but it only requires the formation of traces of a free acid such as butyric acid, totally to spoil a compound. Even an acetate such as linalyl acetate can cause problems by giving rise to free acetic acid. In alkaline media progressive breakdown of the ester may occur as the acid becomes neutralized. In products where this is likely to be a problem terpinyl acetate is often used to replace linalyl acetate. 

The volatile oil components in cardamom are summarized by Guenther (1975). The first detailed analysis of the oil was reported by Nigam et al. (1965). The oil has little mono- or sesquiterpenic hydrocarbons and is dominated by oxygenated compounds, all of which are potential aroma compounds. While many of the identified compounds (alcohols, esters and aldehydes) are commonly found in many spice oils (or even volatiles of many different foods), the dominance of the ether, 1,8-cineole and the esters, a-terpinyl and linalyl acetates in the composition make the cardamom volatiles a unique combination (Lewis et al., 1966 Salzer, 1975 Korikanthimath et al., 1997). 

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