Terpenes oxygenated derivatives

Volatile compounds are often involved in long distance attraction and are especially important as attractants and repellents (as defined by Kogan, ). One major class of volatile materials, essential oils, is comprised of complex mixtures of terpenes, phenylpropanoid derived compounds and a number of esters, alcohols, aldehydes, ketones, acids, and hydrocarbons. The constituent compounds are mostly of low to medium molecular weight and generally not highly oxygenated. Some of the biological properties of these compounds have been reviewed (17,41,46,55,56). 

Other compounds, containing sulphur or nitrogen, may be present in some oils (like onion, garlic).Investigations on the solubility of pure essential-oil components in carbon dioxide showed that the separation of terpene hydrocarbons and oxygenated derivatives by fractionated extraction is difficult, since their solubility behaviours and vapour pressures are almost the same. Saturating the CO2 with water as modifier can increase the differences in solubility [78],... 

Comparison of the volatile constituents of the oils resulted in the conclusion that the concentrations of terpene hydrocarbons (like pinene, limonene) were higher in the distilled oils, while those of the oxygenated derivatives (like thymol, bomeol, carvone, apiole) were higher in SFE products. 

The most important of all of the oxygen derivatives of the terpene hydrocarbons are those of the di-cyclic group. Of these the most common is the well-known substance camphor, also termed Japan camphor. It is a ketone derivative of a di-cyclic terpene of the cam-phane type known as Bomylene. The corresponding alcohol derivative is known as Bomeol, or Borneo camphor. 

Pure essential oils are mixtures of more than 200 components, normally mixtures of terpenes or phenyl-propanic derivatives, in which the chemical and structural differences between compounds are minimal. They can be essentially classified into two groups A volatile fraction, constituting 90-95% of the oil in weight, containing the monoterpene and sesquiterpene hydrocarbons, as well as their oxygenated derivatives along with aliphatic aldehydes, alcohols, and esters and a nonvolatile residue that comprises 1-10% of the oil, containing hydrocarbons, fatty acids, sterols, carotenoids, waxes, and flavonoids. 

The camphors are oxygen derivatives related to the terpenes they have the formula CioHieO, CioHisO, and C10O20O, are associated with terpenes in plants, and are constituents of many essential oils. The camphors are solid crystalline substances, which are volatile with steam, sublime at low temperatures, and possess characteristic odors. Like the terpenes they are readily converted into benzene derivatives when ordinary camphor is warmed with phosphorus pentoxide cymene is formed. 

Terpenes are natural, unsaturated hydrocarbons derived from isoprene units. They are widely distributed in nature and oxygenated derivatives, commonly named terpenoids, are important flavour compounds. Many of these terpenoids are considered as G S and are us as food additives or as fragrances. 

The most widely occurring terpenes are the smallest molecules, that is, the monoterpenes, CioHjg, and their oxygenated derivatives such as ketones, aldehydes, alcohols, oxides, phenols, along with simple hydrocarbons. Their properties are determined by functional groups—oxygen-containing radicals attached to the carbon skeleton. 

Mono-, sesqui-, di-, and sesterpenes contain the isoprene units linked in a head-to-tail fashion. The triterpenes and carotenoids (tetraterpenes) contain two C15 and C20 units, respectively, linked head to head. Many terpenes are hydrocarbons, but oxygen-containing compounds such as alcohols, aldehydes, or ketones are also found to fall in the class of terpenes. These derivatives are more frequently named as terpenoids. 

The most important natural sources of flavors are the essential oils derived from spices, fruits, and flowers as well as extractives and exudates (resins) from certain plant sources and animal secretions, e.g., musk. Essential oils are aromatic substances which are widely used in several industries such as perfume, pharmaceutical, food, and nutrition. These are mixtures of more than 200 compounds [14,16]. It contains monoterpenes, sesquiterpene hydrocarbons, and their oxygenated derivatives, along with aliphatic and aromatic aldehydes, alcohols, esters, and nonvolatile residues. Generally, terpenes are unsaturated com-... 

Fig. 13.2 Structure and name of selected terpenes and oxygenated derivatives...

The essential oil is composed of terpene and sesquiterpene hydrocarbons and their oxygenated derivatives. While the former predominate in quantity, it is the various oxygenated components that are mainly responsible for the effect of hops on aroma, flavour and the mouth feel of beer. The extraction of these compounds and their recovery undamaged and in good yield are important considerations in the choice of a suitable solvent for hop processing. 

Villanueva et al. reported a comparison between the performance of different green solvents for extracting thymol from different thyme plants. The genus Thymus (Lamiaceae family) is an aromatic plant very rich in essential oil compounds, which are the most valued constituents of the herb. Thyme essential oil is formed by terpenes and its oxygenated derivative compounds (alcohols, aldehydes, ketones, etc.) and is appreciated for food flavoring, in cosmetic, perfumery and in the pharmaceutical industry. 

Violent explosions which occurred at —100 to —180°C in ammonia synthesis gas units were traced to the formation of explosive addition products of dienes and oxides of nitrogen, produced from interaction of nitrogen oxide and oxygen. Laboratory experiments showed that the addition products from 1,3-butadiene or cyclopentadiene formed rapidly at about — 150°C, and ignited or exploded on warming to —35 to — 15°C. The unconjugated propadiene, and alkenes or acetylene reacted slowly and the products did not ignite until +30 to +50°C [1], This type of derivative ( pseudo-nitrosite ) was formerly used (Wallach) to characterise terpene hydrocarbons. Further comments were made later [2],... 

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. 

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