Other aromatic hydrocarbons

Some aromatic hydrocarbons have not been mentioned in the previous sections and will be briefly discussed here. 

Aromatic hydrocarbons which do not have side chains in general form p-quinones and acid anhydrides. Benzene, naphthalene and anthracene have been dealt with above. In the case of phenanthrene, no p-quinone is formed as the adjacent C—H groups of the central nucleus are the most reactive. Phthalic anhydride is the main partial oxidation product, in addition to minor products such as 9,10-phenanthraquinone. Andreikov and 

Relative oxidation rates of some aromatic hydrocarbons 

Rusyanova [25] describe the oxidation of phenanthrene to various products (using the V2Os catalyst above) by power rate equations according to a parallel reaction scheme 

Product inhibition is reported for reactions (1) and (2) in this scheme. Of interest are the relative overall oxidation rates for some aromatic hydrocarbons reported by the authors (Table 38). 

Certain other aromatic hydrocarbons will now be considered briefly. Anthracene is less aromatic than naphthalene. There are fourteen electrons available for the formation of tt bonds and so the full number of 

With the aid of these structures we may obtain an approximate evaluation of the relative unsaturation of the various atoms. This is shown in XII where the figures represent the number of valence bond structures in which a particular carbon atom is involved in a Dewar type bond 

The 9 and lo positions are the most unsaturated and hydrogenation leads to the formation of 9, lo-dihydroanthracene. Not only is the energy of activation for the hydrogenation reaction reduced by the increased unsaturation of the 9 and 10 carbon atoms, but the resulting molecule possesses considerable resonance energy by virtue of the two benzene rings and represents the most stable isomer of dihydroanthracene. 

Naphthacene XV) has five Kekul6 structures and Dewar structures with 

For the hydrocarbons so far considered, which consist of benzene rings connected linearly, the number of Kekul structures is one more than the number of rings. Thus in benzene it is two, naphthalene three, anthracene four, naphthacene five and dibenzanthracene six. The number of structures with elongated tt bonds, however, increases considerably as the number of benzene rings in the molecule is increased and it is this fact that is responsible for the gradual increase in reactivity with the size of the molecule. 

The facts that only one monosubstitution product is obtained in many reactions and that no additional products can be prepared show conclusively that benzene has a symmetrical ring structure. Stated differently, every H atom is equivalent to every other H atom, and this is possible only in a symmetrical ring structure (a). 

The debate over the structure and bonding in benzene raged for at least 30 years. In 1865, Friedrich Kekule (1829-1896) suggested that the structure of benzene was intermediate between two structures [part (b) of the structures shown above] that we now call resonance structures. We often represent benzene as 

A computer-generated model of a molecule of benzene, CgHe. 

0 A model of toluene, C5H5CH3. This is a derivative of benzene in which one H atom has been replaced by a methyl group. 

Each of these products contains compounds based on the benzene ring. 

---

Values of the diamagnetic anisotropy of benzene and other aromatic hydrocarbon molecules are calculated on the basis of the assumption that the p, electrons (one per aromatic carbon atom) are free to move from carbon atom to adjacent carbon atom under the influence of the impressed fields. When combined with the assumed values for the contributions of the other electrons (-2.0X 10-6 for hydrogen, —4.5 X10 c for aromatic carbon, — 6.0XlO-6 for aliphatic carbon) these lead to principal diamagnetic susceptibilities of molecules in approximate agreement with the available experimental data. The diamagnetic anisotropy of graphite is also discussed. 

Uses It is used as a chemical raw material for a myriad of everyday products such as plastics, detergents, textile fibers, drugs, dyes, and insecticides. It is also found in gasoline with other aromatic hydrocarbons. 

Rabus R, F Widdel (1995) Anaerobic degradation of ethylbenzene and other aromatic hydrocarbons by new denitrifying hacter m. Arch Microbiol 163 96-103. 

Other aromatic hydrocarbons include naphthalene, C10H8, and anthracene, C14H10, whose structures are shown as follows ... 

Silver perchlorate forms solid complexes with aniline, pyridine, toluene, benzene and many other aromatic hydrocarbons [1], A sample of the benzene complex exploded violently on crushing in a mortar. The ethanol complex also exploded similarly, and unspecified perchlorates dissolved in organic solvents were observed to explode [2], Solutions of the perchlorate in benzene are said to be dangerously explosive [3], but this may be in error for the solid benzene complex. The energy released on decomposition of the benzene complex has been calculated as 3.4 kJ/g, some 75% of that for TNT [4],... 

Naphthalene and other aromatic hydrocarbons can be reduced by one electron to produce the anion radical. The reduction can be carried out with sodium in an ether solvent or electrochemically in a polar aprotic solvent. 

The highly aromatic resins are often used as coumarone/indene resin substitutes. A range of soft aromatic resins is available, produced from the alkylation of xylene and other aromatic hydrocarbons with dicyclopentadiene. These are excellent softeners for a wide range of rubbers. In common with other aromatic materials derived from petroleum sources, some of the resins used within the rubber industry are deemed to be carcinogenic. 

At least experiments with fluoranthene and other aromatic hydrocarbons having lower triplet energies than fluoranthene resulted only in fluoranthene singlet emission- this excited singlet appears to be generated directly and not by triplet-triplet annihilation. 

DETOL [De-alkylation of toluene] A process for making benzene by de-alkylating toluene and other aromatic hydrocarbons. Developed by the Houdiy Process and Chemical Company, and generally similar to its Litol process for the same purpose. The catalyst is chromia/alumina. Licensed by Air Products Chemicals. In 1987,12 plants had been licensed. 

Hydeal [Hydrodealkylation] A process for making benzene by de-alkylating other aromatic hydrocarbons. Generally similar to the Litol process. Developed in the 1950s by UOP and Ashland Oil Company, but abandoned in favor of UOP s THDA process. See dealkylation. 

Litol Also called Houdry-Litol. A process for making benzene by dealkylating other aromatic hydrocarbons. It is a complex process which achieves desulfurization, removal of paraffins and naphthenes, and saturation of unsaturated compounds, in addition to dealkylation. The catalyst contains cobalt and molybdenum. Developed by the Houdiy Process and Chemical Company and Bethlehem Steel Corporation. First installed by the Bethlehem Steel Corporation in 1964. Subsequently used at British Steel s benzole refinery, Teesside, England. 

MHC [Mitsubishi hydrocracking] A process for making benzene and other aromatic hydrocarbons by hydrogenating cracked petroleum fractions. 

We employed various substrates to check for MFO in two bivalve species, a salt water mussel (Mytilus edulis) and a fresh water clam (Anodonta sp). Cytochrome P-450 was also studied. Organisms were exposed to 100 PPM Venezuelan crude in a stagnant system for up to one month. Enzyme assays were carried out with digestive gland 9000 g homogenates (17) and cytochrome P-450 analysis, with microsomes (21). The hydrocarbon substrates investigated included 1I+C-labelled benzo(a)pyrene, fluorene, anthracene, and naphthalene. The method used for separation of BP metabolites by thin layer radiochromatography has been described (7). The metabolite detection method for the other aromatic hydrocarbons was essentially the same except methylene chloride was used as metabolite extractant as well as TLC developer. Besides the hydrocarbon substrates, we also checked for other MFO reactions, N-dealkylase with C-imipramine (22) and 0-dealkylase with ethoxycoumarin (15). 

Chemical/Physical. Kanno et al. (1982) studied the aqueous reaction of benzene and other aromatic hydrocarbons (toluene, xylene, and naphthalene) with hypochlorous acid in the presence of ammonium ion. They reported that the aromatic ring was not chlorinated as expected (forming chlorobenzene) but was cleaved by chloramine forming cyanogen chloride (Kanno et al, 1982). 

Chemical/Physical. Under atmospheric conditions, the gas-phase reaction of o-xylene with OH radicals and nitrogen oxides resulted in the formation of o-tolualdehyde, o-methylbenzyl nitrate, nitro-o-xylenes, 2,3-and 3,4-dimethylphenol (Atkinson, 1990). Kanno et al. (1982) studied the aqueous reaction of o-xylene and other aromatic hydrocarbons (benzene, toluene, w and p-xylene, and naphthalene) with hypochlorous acid in the presence of ammonium ion. They reported that the aromatic ring was not chlorinated as expected but was cleaved by chloramine forming cyanogen chloride. The amount of cyanogen chloride formed increased at lower pHs (Kanno et al., 1982). In the gas phase, o-xylene reacted with nitrate radicals in purified air forming the following products 5-nitro-2-methyltoluene and 6-nitro-2-methyltoluene, o-methylbenzaldehyde, and an aryl nitrate (Chiodini et ah, 1993). 

There are many other aromatic hydrocarbons, i.e. compounds like benzene, which contain rings of six carbon atoms stabilised by electron delocalisation. For example, if one of the hydrogen atoms in benzene is replaced by a methyl group, then a hydrocarbon called methylbenzene (or toluene) is formed. It has the structural formulae shown. Methylbenzene can be regarded as a substituted alkane. One of the hydrogen atoms in methane has been substituted by a or —group, which is known as a phenyl group. So an alternative name for methylbenzene is phenylmethane. Other examples of aromatic hydrocarbons include naphthalene and anthracene. 

Like benzene, other aromatic hydrocarbons will undergo electrophilic substitution reactions. 

Coal tar naphtha is primarily a mixture of toluene, xylene, cumene, benzene, and other aromatic hydrocarbons it is distinguished from petroleum naphtha, which is comprised mainly of aliphatic hydrocarbons. ... 

Lyddite. Br expl, similar in compn to the Fr Melinite (qv). The name was derived from the town of Lydd, near which the expl was manufd and tested. It contains either PA alone, or in admixture with about lOp of other aromatic hydrocarbons, added principally to lower the mp of the PA. Lyddite was adopted in 1888 for charging torpedo warheads, and later during the South African war, for HE projectiles Refs 1) Daniel (1902), 414 2) Colver... 

Sauer, T.C., Jr, Sackett, W.M. Jeffrey, L.M. (1978) Volatile liquid hydrocarbotrs in the surface coastal waters of the Gulf of Mexico. Marine Chem., 1, 1-16 Seifert, B. Abraham, H.-J. (1982) Indoor air concentratiotrs of benzene and some other aromatic hydrocarbons. Ecotoxicol. environ. Saf, 6, 190-192 Shah, J.J. Heyerdahl, E.K. (1988) National Ambient Volatile Organic Compounds (VOCs) Data Base Update (EPA 600/3-88/0 lOA), Research Triangle Park, NC, Environmental Protection Agency, Atmospheric Sciences Research Laboratory ... 

It is certain that, in the first reduction step in aprotic solvents, an electron is accepted by the LUMO of the organic compound. However, it was fortunate that this conclusion was deduced from studies that either ignored the influence of solvation energies or used the results in different solvents. Recently, Shalev and Evans [55] estimated the values of AG V(Q/Q ) for 22 substituted nitrobenzenes and nine quinones from the half-wave potentials measured by cyclic voltammetry. For quinones and some substituted nitrobenzenes, the values of AG V(Q/Q ) in a given solvent were almost independent of the EA values. Similar results had been observed for other aromatic hydrocarbons in AN (Section 8.3.2) [56]. If AG V(Q/ Q ) does not vary with EA, there should be a linear relation of unit slope between El/2 and EA. Shalev and Evans [55], moreover, obtained a near-linear relation between AG V(Q/Q ) and EA for some other substituted nitrobenzenes. Here again, the Ey2-EA relation should be linear, although the slope deviates from unity.8)... 

Although most of the experiments were carried out using p-xylene as substrate, several exploratory runs were made using other aromatic hydrocarbons. These are summarized in Table I. Maximum yields were not determined. Alkylnaphthalenes gave highly colored oxidates, from which only small amounts of naphthoic and naphthalic acids could be isolated. Oxidation of anthracene gave virtually quantitative yields of anthraquinone under extremely mild conditions (10). 

The distances between saturated hydrocarbon molecules in crystals can be calculated by the use of these radii, with consideration also of the possibility of molecular or group rotation. Another factor must be introduced for aromatic molecules.64 The double bonds in these molecules project above and below the plane of the ring in such a way as to give to the ring an effective thickness of about 3.4 A, as observed in anthracene, durene, hexamethylbenzene, benzbisantkrene, and many other aromatic hydrocarbons. The same value is also found between the layer of graphite. 

Eleven other aromatic hydrocarbons Acetone Water... 

---