Volatile alcohols, aldehydes, ketones

For more volatile compounds in soils, such as aromatic hydrocarbons, alcohols, aldehydes, ketones, chloroaliphatic hydrocarbons, haloaromatic hydrocarbons, acetonitrile, acrylonitrile and mixtures of organic compounds a combination of gas chromatography with purge and trap analysis is extremely useful. Pyrolysis gas chromatography has also found several applications, heteroaromatic hydrocarbons, polyaromatic hydrocarbons, polymers and haloaromatic compounds and this technique has been coupled with mass spectrometry, (aliphatic and aromatic hydrocarbons and mixtures of organic compounds). 

The volatile components from coal pyrolysis are primarily small hydrocarbons and oxygen-containing molecules. By adding H2O and limited O2 and while heating coal, these products incorporate considerable 0 atoms into the volatile products to form alcohols, aldehydes, ketones, and acids. However, these products consist of many molecules that... 

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). 

Surface lipids of plants. The thick cuticle (Fig. 1-6) that covers the outer surfaces of green plants consists largely of waxes and other lipids but also contains a complex polymeric matrix of cutin (stems and leaves) or suberin (roots and wound surfaces).135/135a Plant waxes commonly have C10 - C30 chains in both acid and alcohol components. Methyl branches are frequently present. A major function of the waxes is to inhibit evaporation of water and to protect the outer cell layer. In addition, the methyl branched components may inhibit enzymatic breakdown by microbes. Free fatty acids, free alcohols, aldehydes, ketones, 13-dike tones, and alkanes are also present in plant surface waxes. Chain lengths are usually C20 - C35.136 Hydrocarbon formation can occur in other parts of a plant as well as in the cuticle. Thus, normal heptane constitutes up to 98% of the volatile portion of the turpentine of Pin us jeffreyi.81... 

Condensed-Phase Mechanisms. The mode of action of phosphorus-based flame retardants in cellulnsic sy stems is probably best understood. Cellulose decomposes by a noncalalyzed route lo tarry depolymerization products, notably levoglucosan, which then decomposes to volatile combustible fragments such as alcohols, aldehydes, ketones, and hydrocarbons. However, when catalyzed by acids, the decomposition of cellulose proceeds primarily as an endothermic dehydration of the carbohydrate to water vapor and char. Phosphoric acid is particularly efficaceous in this catalytic role because of its low volatility (see Phosphoric Acids and Phosphales). Also, when strongly heated, phosphoric acid yields polyphosphoric acid which is even more effective in catalyzing the cellulose dehydration reaction. The flame-retardanl action is believed to proceed by way of initial phosphory lation of the cellulose. 

The physical characters of greatest importance in the examination of the volatile oils are, besides appearance and odour specific gravity, rotatory power, refractive index, solidifying point, behaviour on distillation, and solubility see sections 1-7). The components most often requiring estimation are esters, alcohols, aldehydes, ketones, phenols (see sections 8-11), and the most common adulterants to be looked for are alcohol,... 

In summary, large molecules tend to be more persistent than smaller ones, though this may be modified by the presence of functional groups, which cause polarization and hydrogen bonding. For an equivalent molecular size, hydrocarbons and ethers are more volatile than aldehydes, ketones, and esters, which are in turn more volatile than alcohols and acids. 

Nearly 1000 compounds have so far been identified in the volatile constituents of meat from beef, chicken, mutton and pork (6). The largest number of volatiles has been determined in beef and these were representative of most classes of organic compounds. Hydrocarbons, alcohols, aldehydes, ketones, carboxylic acids, esters, lactones, ethers, sulfur and halogenated compounds as well as different classes of heterocyclic substances (Figure 1) namely furans, pyrldlnes, pyrazines, pyrroles, oxazol(in)es, thiazol(in)es, thiophenes were present in cooked meat flavor volatiles as shown in Table I. Many of these compounds are unimportant to the flavor of meat and some may have been artifacts (16). 

Molds while growing produce various chemicals as a result of their primary metabolic processes. These processes are needed to ensure the continuation of the mold s life cycle. The gaseous metabolic products are collectively referred to as microbial volatile organic compounds (mVOCs). Some mVOCs are primary solvents and are chemically identical to those originating from solvent-based building materials and cleaning supplies (e.g., alcohols, aldehydes, ketones, hexane, methylene chloride, benzene, and acetone). 

Biologically generated aromas are frequently quite complex and include a wide range of polarities. For example, strawberries have been shown to possess more than 350 volatile compounds ( 1). In addition, the classes of compounds frequently encountered in biological materials includes alcohols, aldehydes, ketones, esters, ethers, sulfides, mercaptans, amines, aromatic and heterocyclic compounds and hydrocarbons. Representative classes of compounds identified in strawberries are indicated in Table I. 

The essence of citrus flavor is a complex mixture of volatile alcohols, aldehydes, esters, hydrocarbons, ketones and oxides. Alcohols are the largest class and ethanol is the main organic constituent of the essence. Esters and aldehydes are considered to contribute most to the characteristic flavor and aroma. In these two classes ethyl butyrate and acetaldehyde were shown to be important components of high quality orange juice (1). 

The flavor of fish and seafoods is composed of taste-active low molecular-weight extractives and aroma-active compounds. The taste-active compoimds are more abundant in the tissues of mollusks and crustaceans than fish. The most important non-volatile taste components are fi-ee amino acids, nucleotides, inorganic salts and quaternary ammonia bases. Alcohols, aldehydes, ketones, furans, nitrogen-containing compounds, sulfur-containing compounds, hydrocarbons, esters and phenols are the most important volatiles is shellfish. Alkyl pyrazines and sulfur-containing compounds are important contributors to the cooked aroma of crustaceans. Furans pyrazines, and Lactones have been found in heat-treated seafoods. Dimethyl disulfide, dimethyl trisulfide, heterocyclic sulfiir-containing compounds (alkylthiophenes) have been found in most thermally treated crustaceans like prawn, crab, oyster, crayfish and shrimp (52). 

The aromas associated widi very fi esh fish are usually mild, delicate and fi esh (53,54), and generally described as green (hexanal), melon-like ((E,Z)-3,6-nonadienal), iodine-like (bromophenols). Fresh fish and seafood aromas are due to volatile carbonyls and derive fi om lipoxygenase catalyzed oxidation of polyunsaturated fatty acids. The oxidation of Eicosapentaenoic acid (C20 5) leads to C5 to C9 alcohols, aldehydes, ketones and hydrocarbons. The formation of methyl mercaptan, dimethyl sulfide and dimethyl disulfide in fi esh fish at the time of harvest has been reported by Shiomi et al. (55). Although these compounds are usually associated with fish deterioration, they contribute to the fi esh aroma ch cter at low concentrations. For instance, dimethyl sulfide is... 

Essential oils are volatile, odorous principles consisting of terpene alcohols, aldehydes, ketones and esters (>90%) and/or phenylpropane derivatives. Aetherolea are soluble in ethanol, but only to a very limited extent in water. They are mostly obtained by steam distillation of plant material. 

Oxidation of VOCs leads to the formation of more highly substituted and therefore lower volatility reaction products. The reduction in volatility is due mainly to the fact that adding oxygen and/or nitrogen to organic molecules reduces volatility (Seinfeld and Pankow 2003). Addition of carboxylic acid, alcohol, aldehyde, ketone, alkyl nitrate, and nitro groups to the precursor VOC can reduce its volatility by several orders of magnitude (see Section 14.5.1). The reactions of VOCs with 03, OH, and N03 can all lead to SOA formation in the atmosphere. 

The book by Burchfield and Storrs (1962) on biochemical applications of gas chromatography contains a goldmine of information about the separation of substances of interest to investigators in many fields, for example, fatty acids and esters, volatile amines and amino alcohols, aldehydes, ketones, thiols, sulfides, and volatile... 

Essential oils are natural substances mainly obtained from vegetable raw materials either by distillation with water or steam or by a mechanical process (expression) from the epicarp of citrus fruits. They are concentrated fragrance and avor materials of complex composition, in general volatile alcohols, aldehydes, ethers, esters, hydrocarbons, ketones, and phenols of the group of mono- and sesquiterpenes or phenylpropanes as well as nonvolatile lactones and waxes. 

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. 

Volatile products of combustion - styrene, oligomers, organic acids, Alcohols, aldehydes, ketones, CO, CO ... 

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