Ethereal Oils, Terpenes

Coffee oil is generally described as the petroleum ether-soluble fraction from green coffee beans. Arabica coffees contain 11.1 to 13.6% oil, whereas Robusta coffees contain only 4.4 to 4.8% oil.106 Triglycerides constitute 79% of this oil, terpene esters 17%, and the remaining 4% is contributed by sterols, free terpenes, tocopherols, and as yet unknown... 

Soluble in ethanol, ether (Weast, 1986), benzene, chloroform, acetone, petroleum ether, fixed oils, terpenes, and aqueous alkaline solutions (Windholz et al., 1983). Also soluble in cyclic ethers such as tetrahydrofuran. 

The first suitable representative of this class of substances, 6-methyl-5-heptene-2-one, was investigated by Neuberg and Lewite. This ketone, which is a natural constituent of ethereal oils, can also be obtained by degradation of various aliphatic and cyclic terpenes. By means of fermenting yeast it is converted to 6-methyl-5-heptene-2-ol,... 

WALLACH, OTTO (1847-1931). German chemist who received the Nobel prize for chemistry in 1910 for recognition of his services to organic chemistry and the chemical industry by his pioneer work tn the field of alic.yclic compounds. His mentors were Hofmann and Wahler, and he worked at the University of Bonn under Kekule. He studied pharmacy and did work on terpenes. camphors, and essential oils. This was followed by research in aromatic oils, perfumes, and spices. His research of terpenes revealed their significance in sex hormones and vitamins. Ethereal oils and industrial uses were made possible by his work. 

Spices impart aroma, colour and taste to food preparations and sometimes mask undesirable odours. Volatile oils give the aroma, and oleoresins impart the taste. Aroma compounds play a significant role in the production of flavourants, which are used in the food industry to flavour, improve and increase the appeal of their products. They are classified by functional groups, e.g. alcohols, aldehydes, amines, esters, ethers, ketones, terpenes, thiols and other miscellaneous compounds. In spices, the volatile oils constitute these components (Zachariah, 1995 Menon, 2000). 

Terpenes and Camphor.—The importance of these two phenols is in their natural occurrence as ethers in ethereal oils of many plants, e.g., oil of thyme and oil of caraway, and especially in their relationship to the terpenes and camphor, as will be shown later (p. 826, 834). 

Strictly speaking the terpenes are hydrocarbons which are present in, or are obtained by steam distillation from, certain natural products, such as camphor and oil of turpentine certain of the so-called essential or ethereal oils, mostly from conifer or citrus plants, e.g., oil of lemon various plant resins, and India rubber or caoutchouc. They are the mother substances of the individual constituents of the products just mentioned. In general usage the name terpenes includes not only the hydrocarbons but the various derivatives referred to above. 

The simpler group in constitution is that of the olefine terpenes. This group is represented by terpenes obtained from the ethereal oils of lemon, orange, rose, geranium, etc., and from india rubber or caoutchouc. 

In the preceding discussion of the terpenes we have frequently referred to essential oils or as they are also termed ethereal oils. These names, however, do not apply to a distinct chemical group of com-... 

Use Solvent for protective coatings, polishes, and waxes synthesis of camphene, camphor, geraniol, terpin hydrate, terpineol, synthetic pine oil, terpene esters and ethers, lubricating oil additives, flavoring odorant. 

Dimorphous crystals, mp 55.5° and mp 66° (ligroin), Said to be odorless when very pure, but usually a phenolic odor persists, bp 235% Volatile with steam. One gram dissolves in 260 ml water at 20°, more sol in hot water. Freely sol in alcohol, benzene, chloroform, ether, acetone, petr ether, fixed oils, terpenes, aq alkaline solns. Aq solns turn yellow on exposure to llghr and air. 

Crystals from benzene, mp 115.5. Phenolic odor- Volatile with steam, bp 246. One gram dissolves in 3 liters of water at 20. More stahle in hot water. Soluble in 1 part of 95% alcohol, ether, benzene, terpenes, fixed oils, in solns of alkali hydroxides. 

Qualitative and quantitative analysis of ethereal oils is usually aehieved by gas-ehromatography (GC), and the eombination of this method of separation with mass speetrometry (GC-MS) for identifieation. Pure terpenes are obtained on a larger scale from ethereal oils by distillation ehromatographie methods of separation predominantly in the gas (GC) or liquid phase (LC) permit the isolation of small amounts with high purities. 

The strikingly different odors of cis-trorw-isomers and diastereomers is demonstrated by various other pairs of terpenes. For example, the synthetie fragranee (E)-S-methyl-a-ionone has a lovely flowery smell like the blossoms of violets, whereas the (Z)-isomer emits a woody tobaceo-like odor. Likewise, the strongly woody smelling sesquiterpene (-)- /-y-eudesmol from Algerian oil of geranium eontrasts wifli the almost odorless diastereomer (-l-)-y-eudesmol whieh is wide-spread among ethereal oils. 

More sensitive human noses can even distinguish between enantiomeric terpene hydrocarbons (i )-(+)-Limonene, the major constituent of the ethereal oil of mandarin peels, is recognized as a characteristic clean orange fragrance, while the (S)-(-)-enantiomer from the oil of fir-cones radiates a less pleasant orange odor with a touch of turpentine. Fig. 15 illustrates the sensitivity of the human olfactory organ by means of the limonene enantiomers between it may differentiate. 

Ascaridol. Several ketonic and aldehydic terpenes have been determined polarographically in ethereal oils, seeds, drug portions and in other materials. Recently, interest has been shown in the determination of the terpene peroxide, ascaridol. The determina-tion consists of dissolving 100 mg of the oil in 100 ml. of ethanol, and mixing an aliquot portion with the same volume of 0 2 N lithium sulphate. The wave at —0 9 V gives the content of ascaridol, e.g. in Oleum Chenopodii or in Oleum Boldo. 

Of the 10 constituents which represent nearly half the oil of neroH, only linalool (10) can be said to contribute direcdy to the characteristic aroma of orange flower oil. In 1977, IFF chemists performed an in-depth analysis of this oil and identified three simple terpenic compounds, each present at less than 0.01%, a-terpenyl methyl ether [1457-68-0] (31), geranyl methyl ether [2565-82-4] (32), andhnalyl methyl ether [60763-44-2] (33) (11). The latter two compounds possess green floral-citms aromas and have been known to perfumery for some time a-terpenyl methyl ether (31) has been called the orange flower ether by IFF chemists owing to its characteristic odor. 

Principal terpene alcohol components of piae oils are a-terpiueol, y-terpiueol, P-terpiueol, a-fenchol, bomeol, terpiuen-l-ol, and terpiaen-4-ol. The ethers, 1,4- and 1,8-ciaeole, are also formed by cycli2ation of the p-v( enthane-1,4- and 1,8-diols. The bicycHc alcohols, a-fenchol [512-13-0] (61) and bomeol (62), are also formed by the Wagner-Meerweiu rearrangement of the piaanyl carbonium ion and subsequent hydration. Bomeol is i7(9-l,7,7-trimethylbicyclo[2.2.1]heptan-2-ol [507-70-0]. Many other components of piae oils are also found, depending on the source of the turpentine used and the method of production. 

The identification of camphene is best carried out by its conversion into isobomeol under the influence of acetic acid in the presence of sulphuric acid. In order to effect this conversion, 100 grams of the fraction containing the terpene in substantial quantity are mixed with 250 grains of glacial acetic acid and 10 grams of 50 per cent, sulphuric acid. Tne mixture is heated for two to three hours on a water-bath to a temperature of 50° to 60°. At first the liquid separates into two layers, bat soon becomes homogeneous and takes on a pale red colour. Excess of water is added, and the oil which is precipitated, and which contains the isobomeol in the form of its acetate, is well washed with water repeatedly. It is then saponified by heating with alcoholic potash solution on a water-bath. The liquid is then evaporated and extracted with water, and the residue recrystallised from petroleum ether. 

Sylvestrene nitrosochloride, CjoHj,. NOCl, is prepared from pure sylvestrene, regenerated from the dihydrochloride in the following manner Four volumes of the terpene are dissolved in six of amyl nitrite and five volumes of strong hydrochloric acid are added, with constant shaking. The heavy oil which separates is shaken with a little ethyl alcohol, when it solidifies, and can be purified by dissolving it in chloroform and precipitating it with petroleum ether. It is finally recrystallised from methyl alcohol, when it melts at 106° to 107°. 

After separation of neroli oil, the aqueous layer of the steam distillate, known as orange blossom water, is extracted with suitable solvents (e.g., petroleum ether). Evaporation gives orange flower water absolute (absolue de Teau de fleurs d oranger), which is a dark brown-red liquid. It contains less terpene hydrocarbons and correspondingly more polar compounds than neroli oil. 

Indonesian oils contain ca. 90% terpene hydrocarbons, mainly sabinene (14-29%) and a- (15-28%) and /3-pinene (13-18%). Major oxygen-containing constituents are l-terpinen-4-ol (2 6%) and phenol ether derivatives like myristicine (5-12%) [646-650cj. 

The odor of a freshly crushed mint leaf, like many plant odors, is due to the presence in the plant of volatile C10 and Ci5 compounds, which are called terpenes. Isolation of these substances from the various parts of plants, even from the wood in some cases, by steam distillation or ether extraction gives what are known as essential oils. These are widely used in perfumery, as food flavorings and medicines, and as solvents. Among the typical essential oils are those obtained from cloves, roses, lavender, citronella, eucalyptus, peppermint, camphor, sandalwood, cedar, and turpentine. Such substances are of interest to us here because, as was pointed out by Wallach in 1887 and reemphasized by Ruzicka in 1935, the components of the essential oils can be regarded as derived from isoprene ... 

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