Terpene hydrocarbons, oxidation

Dicarbonyls. A third area of uncertainty is the treatment of dicarbonyls formed from aromatic or terpene hydrocarbon oxidation. (The simplest is glyoxal, CHOCHO, but a large number have been identified, 47. The yields and subsequent reactions of these compounds represent a major area of uncertainty in urban air photochemistry (186) and since they may be a significant source of HOjj through photolysis, inaccuracies in their portrayal may result in errors in calculated values of HO. and HO2.. 

Ordinarily, the atmosphere is a self-cleansing system due to the abundance of O3, OH, NO2, and other reactive species. For example, hydrocarbon emissions from biota (such as terpenes) are oxidized in a matter of hours or days to CO and then on to CO2. Alternatively, carboxylic acids may be formed and then transferred to the hydrosphere or pedosphere by rain. The atmosphere acts much like a low-temperature flame, converting numerous reduced compounds to oxidized ones that are more readily removed from the air. The limit to the rate of oxidation can be defined by the concentration of OH... 

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],... 

For this sample the results show identification of 13 major components out of 289, making up 81.25% of the total components. The volatile monoterpene -pinene (peak 1) is the first off the column. The alcohols citronellol (10) and geraniol (11) are responsible for the odour characteristics of geranium, which is lifted and activated by the two rose oxides (2 and 3). The 6,9-guaiadiene (7) is a non-terpene hydrocarbon that acts as a back note but it is not a powerful odour. Component 12 is geranyl butyrate component 13 is epi—eudesmol. Chromatograms and data supplied by Jenny Warden of Traceability. 

In the course of an examination of the autoxidation of terpene hydrocarbons, Bardyshev and Shavyrin have found, predictably, that those containing conjugated double bonds e.g. allo-ocimene, myrcene) are oxidized most rapidly, those with isolated double bonds or cyclopropane rings more slowly e.g. limon-ene, carene), and those with a single double bond slowest e.g. pinene). The effect of light, heat, and inhibitors was studied. ... 

The hydrocarbons of the various groups which we have just discussed are the true terpenes. On oxidation these yield alcohol and aldehyde or ketone derivatives. The olefine terpenes, only, yield aldehydes that occur as constituents of natural products known as essential oils (p. 840). The derivatives of both groups of cyclic terpenes which are present in essential oils and plant gums and resins are either secondary alcohols or ketones. Among these latter are the camphors of which common camphor is the most important and best known example. In a general sense all of the oxidation products of the cyclic terpenes are termed camphors. 

Citrus fruits contain peel oil, the essence from which oil is obtained during concentration of the juice process. Citrus oils are characterized by a high percentage of terpene hydrocarbons (limonene, C10H16), which contribute little to aroma. The unique characteristics of limonene are its relative insolubility in dilute alcohol and its susceptibility to oxidation, causing off-flavor production. If the monoterpenes are removed, the resulting oil is called terpene-free or terpeneless oil. Aldehydes, esters, and alcohols are the main contributors to the aromas of citrus oil. These compounds are relatively polar and soluble in water therefore, they are satisfactory for applications in food and beverage. 

In the atmosphere, hydrocarbons are subject to attack by OH radicals and ozone which initiate an oxidation mechanism whereby the materials are first converted to oxygenated compounds and then partly to CO. Hydrocarbon oxidation mechanisms are discussed in Section 6.3. Here we note that not every carbon atom is converted to CO. Accordingly, a yield estimate is required if one wishes to utilize the above data in estimating the production of CO from the oxidation of hydrocarbons. For isoprene the oxidation mechanism has been staked out and one expects a conversion yield of 80% CO, 20% C02. A laboratory study of Hanst et al. (1980) has essentially confirmed these yields. Terpenes, by contrast, pose much large uncertainties, because a substantial portion of the material may be converted to low-volatility products, which condense onto aerosol particles (see Section 7.4.3). The experiments of Hanst et al. (1980) on a-pinene indicated a total yield of CO + C02 of 30% and a CO/C02 ratio of 0.7. Thus, about 20% of carbon in a-pinene was converted to CO. If the conversion efficiencies for other terpenes were similar, one would obtain the following CO... 

Monoterpenes A terpene molecule contains 10 carbon atoms (derived from two isoprene units) and at least one double bond. Terpene hydrocarbons are thermally labile and easily oxidized and, thus, citrus oils, which contain a high level of terpenes, do not keep well. Some terpenes are thought to have... 

Oleoresin 0-le-o- re-z n [ISV] (ca. 1846) n. Pine gum, the non-aqueous secretion of resin acids dissolved in a terpene hydrocarbon oil, which is (1) Produced or exuded from the intercellular resin ducts of a living tree. (2) Accumulated, together with oxidation products, in the dead wood of weathered limbs and stumps. Note—The... 

Saeki, M. and N. Hashimoto, 1968. Microbial transformation of terpene hydrocarbons. Part I. Oxidation products of li limonene and [Pg.904]

The term terpene is used to describe a compound, which is a constituent of an essential oil containing carbon and hydrogen or carbon atoms, hydrogen, and oxygen atoms, and is not aromatic in character [24, 25]. This definition is usually extended to include other compounds called terpenoids, which are not of natural occurrence but are very closely related to the natural terpenes. Most terpenes, which include terpenoids, are invariably hydrocarbons, alcohols, aldehydes, ketones, or oxides, and they may be solids or liquids. Terpene hydrocarbons are usually liquids, while terpenes of higher molecular weights, mostly obtained from the natural gums and resins of plants and trees, are not steam volatile. 

Although terpene hydrocarbons, especially monoterpenes, are the most abundant constituents of citrus peels oil, they serve only as a flavor carrier and contribute little to flavor on their own (23). These terpenoid hydrocarbons are usually removed by deterpenation in order to increase the concentration of flavor and fragrance compounds. Furthermore, unsaturated hydrocarbons (terpenes) are unstable to heat and light, and may oxidize rapidly to produce undesirable off-flavor compounds that adversely affect the desirable aroma of products (24). Therefore, concentrated and deterpenated oils have become popular in the citrus oil market. 

Features Good tack and adhesion high m.w. compat. with resins, film-formers, and oils resist, to oxidation reactive hydroxyl group low volatility Regulate FDA 21CFR 175.105,176.180,176.210,177.2600 SARA 311/312 Immediate (acite) Hazard, 313 nonreportable Australia AlCS, Canada DSL, China lECSC, Japan Mill, Philippines PICCS listed Properties Colorless, tacky resin mild pleasant odor sol. in common org. soivs. incl. alcohols, esters, ketones, chlorinated soivs., aliphatic, aromatic or terpene hydrocarbons insoi. in water sp.gr. 1.008 vise. 6500 mPa-s (50 C) acid no. 0.1 sapon. no. 26 ref. index 1.5236 (20 C) 100% act. 

Resin and Resinoid. Natural resins are plant exudates formed by the oxidation of terpenes. Many are acids or acid anhydrides. Prepared resins are made from oleoresins from which the essential oil has been removed. A resinoid is prepared by hydrocarbon extraction of a natural resin. 

Linalool has been used to prepare a mixture of terpenes useful for enhancing the aroma or taste of foodstuffs, chewing gums, and perfume compositions. Aqueous citric acid reaction at 100°C converts the linalool (3) to a complex mixture. A few of the components include a-terpineol (34%) (9), Bois de Rose oxide (5.1%) (64), ocimene quintoxide (0.5%) (65), linalool oxide (0.3%) (66), tij -ocimenol (3.28%) (67), and many other alcohols and hydrocarbons (131). 

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