Arenes or Aromatic Hydrocarbons

Arenes are cyclic hydrocarbons derived from benzene. At room temperature, they are liquids or solids. Benzene is by far the most important arene and is among the twenty most important chemical products. Its annual world production is in excess of 6 million tons. It forms the basis for a very large number of products plastics, resins, dye stuffs, explosives, detergents, insecticides, and synthetic fibres. 

Benzene CeHg has no action on aluminium, even as a mixture with alcohol. Aluminium equipment is used for the distillation (boiling point 80 °C), storage and transportation of benzene and its derivatives, such as toluene C6H5CH3, xylene C6H4(CH3)2, ethylbenzene C6H5C2H5, styrene C6H5C2H3 [4]. 

Aromatic hydrocarbons with condensed benzene rings such as naphthalene CioHg, anthracene C]4Hio and their derivatives have no action on aluminium alloys that are used in equipment for their distillation, condensation and storage. 

Terphenyls C6H5C6H4C6H5 are liquids with a boiling point close to 350 °C. They are chemically very stable (their flame point is in excess of 500 °C). Their thermal conductivity is sufficiently high to allow their use as heat exchanger fluid in certain applications such as thermal solar energy plants and heat exchangers. 

Tests performed at 450 °C over 200 h with sheet in 1199, 1050, 5754 and 7049 have shown that these alloys are not attacked, but only stained in anhydrous ( 15 ppm water), degassed terphenyl. 

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Benzene is the parent of a class of hydrocarbons called arenes, or aromatic hydrocarbons. 

EPA Method 25A is the instrumental analyzer method for determination of total gaseous organic concentration using a flame ionization analyzer. The method apphes to the measurement of total gaseous organic concentration of vapors consisting primarily of alkanes, alkenes, and/or arenes (aromatic hydrocarbons). The concentration is expressed in terms of propane (or other appropriate organic calibration gas) or in terms or carrion. 

Aromatic hydrocarbons, sometimes referred to as arenes, can be considered to be derived from benzene, C6H6. Benzene is a transparent, volatile liquid (bp = 80°C) that was discovered by Michael Faraday in 1825. Its formula, C6H6, suggests a high degree of unsaturadon, yet its properties are quite different from those of alkenes or alkynes. 

It is sometimes assumed that every phenol metabolite indicates the formation of an arene oxide intermediate however, as discussed above, arene oxides are not obligate intermediates in the formation of phenols. This is an important distinction because arene oxides and other epoxides are reactive intermediates that can be toxic or even carcinogenic, e.g., epoxides of some polycyclic aromatic hydrocarbons. The question of whether their formation is obligatory is significant for drug design and development and has implications for toxicity as discussed in Chapter 8. 

Aromatic hydrocarbons (or arenes) are a subset of the larger set of hydrocarbons and the simplest of these Is benzene. It is a colourless liquid and has a molecular formula of C H. The molecular formula shows that benzene Is deficient in hydrogen atoms and suggests that It Is an unsaturated hydrocarbon. 

The metabolism of 1,4-dichlorobenzene could involve the formation of an arene oxide intermediate, as has been proposed to occur in the oxidative metabolism of many halogenated aromatic hydrocarbons (Jerina and Daly 1974). 1,4-Dichlorobenzene has not been shown to be mutagenic in microbial or mammalian systems, a result that may be viewed as further suggestive evidence that an arene oxide intermediate is not involved in its metabolism. 

Fullerenes can be derivatized by various means. For example, reaction with fluorine gas proceeds stepwise to the formation of colorless CeoFeo, which, according to the 19F nuclear magnetic resonance (NMR) spectrum, contains just one type of F site and so evidently retains a high degree of symmetry.9 In view of the low adhesion typical of fluorocarbons, this spherical molecule is expected to have extraordinary lubricant properties. Curiously, bromination of Ceo is reversible on heating otherwise, the reactions of fullerenes resemble those of alkenes or arenes (aromatic hydrocarbons). 

The reader may notice a terminological inconsistency with respect to other olefin-forming eliminations. The reaction is called dealkylation in spite of the fact that the second product is an alkane or arene. The reasons are historical because the aromatic hydrocarbons (and similarly the alkanes) were held to be the more important components of the products. Dealkanation and dearenation are the proper names for the reactions. 

The so-called aromatic hydrocarbons, or arenes, are cyclic unsaturated compounds that have such strikingly different chemical properties from conjugated alkenes (polyenes) that it is convenient to consider them as a separate class of hydrocarbon. The simplest member is benzene, C6H6, which frequently is represented as a cyclic conjugated molecule of three single and three double carbon-carbon bonds. Actually, all the carbon-carbon bonds are equivalent (see Chapter 1) but it is convenient to represent the structure in the manner shown ... 

Another synthetic method involves treating the parent aromatic hydrocarbon with sodium hypochlorite in water-chloroform, using phase transfer agents like tetrabutylammonium hydrogen sulfate or benzyltrimethylam-monium chloride.15 The epoxides are formed in high yields. The rate is pH dependent, and epoxide formation is most facile at pH 8-9. Many K-region arene oxides like 1,165, acenaphthylene 1,2-oxide (19), 1-azaphenanthrene 5,6-oxide (20), 4-azaphenanthrene 5,6-oxide (21), 1,10-phenanthroIine 5,6-oxide... 

A mixture of arene oxides and quinones is reported to have been formed by the electrochemical oxidation of aromatic hydrocarbons in an atmosphere of oxygen or oxygen-containing gaseous mixtures. The method is patented and details have not been disclosed.37... 

Aromatic hydrocarbons are structurally related to benzene or made up of benzene molecules fused together. These molecules are called arenes to distinguish them from alkanes, alkenes, and alkynes. All atoms in arenes lie in the same plane. In other words, aromatic hydrocarbons are flat. Aromatic molecules have electrons in delocalized tt orbitals that are free to migrate throughout the molecule. 

Much as benzene and phenyl are the simplest aromatic hydrocarbon or arene and aryl group respectively, methane and methyl are the simplest aliphatic hydrocarbon or alkane and alkyl group respectively. The resonance energy of the various halobenzenes may be identified as the negative of the exothermicity of reaction 34. 

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