Reactions of Aromatic Hydrocarbons

Concurrent synthesis of both mono- and dioxygenases has been shown  

The degradation of pyrene by a Mycobacterium sp. involves both di- and monooxygenase activities (Heitkamp et al. 1988). 

Arene oxides can be intermediates in the bacterial transformation of aromatic compounds and initiate rearrangements (NIH shifts) (Dalton et al. 1981 Cerniglia et al. 1984 Adriaens 1994). The formation of arene oxides may plausibly provide one mechanism for the formation of nitro-substituted products during degradation of aromatic compounds when nitrate is present in the medium. This is discussed in Chapter 2. 

Toluene monooxygenases provide alternatives to dioxygenation, and the ortho-mono-oxygenase in Burkholderia (Pseudomonas) cepacia G4 has been shown to be carried 

Xanthobacter sp. strain Py2 was isolated by enrichment on propene that is metabolized by initial metabolism to the epoxide. The monooxygenase that is closely related to aromatic monooxygenases is able to hydroxylate benzene to phenol before degradation, and toluene to a mixture of 2-, 3-, and 4-methylphenols that are not further metabolized (Zhou et al. 1999). 

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Unlike aliphatic hydrocarbons, aromatic hydrocarbons can be sul-phonated and nitrated they also form characteristic molecular compounds with picric acid, styphnic acid and 1 3 5-trinitrobenzene. Many of the reactions of aromatic hydrocarbons will be evident from the following discussion of crystalline derivatives suitable for their characterisation. 

Amides result from the reaction of aromatic hydrocarbons with isocyanates, such as phenyl isocyanate [103-71-9], ia the presence of aluminum chloride. Phenyl isothiocyanate [103-72-0] similarly gives thioanilides (136). 

The yield increased with increasing the ratio of alumina-supported copper(II) bromide to alkoxybenzenes. The size of alkoxy group did not influence significantly the yield and the ratio of p/o. Nonpolar solvents such as benzene and hexane were better than polar solvent. Polar solvents such as chloroform and tetrahydrofiiran decreased the yield. It is suggested that these polar solvents may be strongly adsorbed on the surface of the reagent. The reaction did not proceed in ethanol to be due to the elution of copper(II) bromide from the alumina to the solution. It is known that the reaction of aromatic hydrocarbons with copper(II) halides in nonpolar solvents proceeds between aromatic hydrocarbons and solid copper(II) halides and not between hydrocarbons and dissolved copper(II) halides (ref. 6). 

This section will describe the Friedel-Crafts alkylation reactions of aromatic hydrocarbons with alkenylchlorosilanes containing short chain alkenyl groups such as allyl and vinyl. The reaction will be discussed in terms of the substituent effect on silicon and the arene rings. 

In complex organic molecules calculations of the geometry of excited states and hence predictions of chemiluminescent reactions are very difficult however, as is well known, in polycyclic aromatic hydrocarbons there are relatively small differences in the configurations of the ground state and the excited state. Moreover, the chemiluminescence produced by the reaction of aromatic hydrocarbon radical anions and radical cations is due to simple one-electron transfer reactions, especially in cases where both radical ions are derived from the same aromatic hydrocarbon, as in the reaction between 9.10-diphenyl anthracene radical cation and anion. More complex are radical ion chemiluminescence reactions involving radical ions of different parent compounds, such as the couple naphthalene radical anion/Wurster s blue (see Section VIII. B.). 

Kanno. S.. Nojima. K.. and Ohya, T. Formation of cyanide ion or cyanogen chloride through the cleavage of aromatic rings by nitrous acid or chlorine. IV. On the reaction of aromatic hydrocarbons with hypochlorous acid in the presence of ammonium ion. Chemosphere, ll(7) 663-667,1982. 

The side-chain alkylation reaction of aromatic hydrocarbons has also been studied using unsaturated aromatic olefins, especially styrene. Pines and Wunderlich 43) found that phenylethylated aromatics resulted from the reaction of styrenes with arylalkanes at 80-125° in the presence of sodium with a promoter. The mechanism of reaction is similar to that suggested for monoolefins, but addition does not take place to yield a primary carbanion a resonance stabilized benzylic carbanion is formed [Reaction (23a, b)j. 

Peter Hervey Given was bom in 1918. He was educated at Oxford University, receiving a B.A. in Chemistry in St. Peter s Hall, Oxford, and the M.A. and D.Phil. in the Dyson Perris Laboratory under the direction of Professors D. LI. Hammick and Sir Robert Robinson (who was the Nobel laureate in chemistry for 1947). Given s thesis research dealt with carbonium ion reactions of aromatic hydrocarbons on cracking catalysts (1-. ... 

Anodic substitution reactions of aromatic hydrocarbons have been known since around 1900 [29, 30]. The course of these processes was established primarily by a study of the reaction between naphthalene and acetate ions. Oxidation of naphthalene in the presence of acetate gives 1-acetoxynaphthalene and this was at first taken to indicate trapping of the acetyl radical formed during Kolbe electrolysis of... 

Radical ion pairs also react by proton, atom, or group transfer. We illustrate proton transfer in reactions of aromatic hydrocarbons with tertiary amines. These reactions cause reduction or reductive coupling. In the reduction of naphthalene, the initial ET is followed by H" transfer from cation to anion, forming 67 paired with an aminoalkyl radical the pair combines to generate... 

Exciplex chemiluminescence has been observed by Weller and Zachariasse128 from the flow reactions of aromatic hydrocarbon anions M " and Wurster s Blue Cations Q +. Since the processes... 

During a study of the reactions of aromatic hydrocarbons with the hydrides formed by reducing cobalt(III) acetylacetonate with triisobuty-laluminum, Tyrlik and Michalski (98) observed that some of the cumene solvent is converted to ethylbenzene, e.g.,... 

Terphenyls, like biphenyl, undergo the usual reactions of aromatic hydrocarbons. The ortho- and para- isomers nitrate initially at the 4-position. 

Tertiary amines have also been employed in electron transfer reactions with a variety of different acceptors, including enones, aromatic hydrocarbons, cyanoaro-matics, and stilbene derivatives. These reactions also provide convincing evidence for the intermediacy of aminoalkyl radicals. For example, the photoinduced electron transfer reactions of aromatic hydrocarbons, viz. naphthalene, with tertiary amines result in the reduction of the hydrocarbon as well as reductive coupling [183, 184]. Vinyl-dialkylamines can be envisaged as the complementary dehydrogenation products their formation was confirmed by CIDNP experiments [185]. 

R. Atkinson, J. Arey, Mechanisms of the gas-phase reactions of aromatic hydrocarbons and PAHS with OH and N03 radicals. Polycyclic Aromat. Compd. 27, 15 10 (2007)... 

As an example, it has been suggested 37-) that many anodic substitution reactions of aromatic hydrocarbons are ECEC processes, as shown below for anodic aromatic acetoxylation Eqs. (2-5) ) ... 

Chatteijee, A., Bhattacharya, D., Iwasaki, T. and Ebina, T. A computer simulation study on acylation reaction of aromatic hydrocarbons over acidic zeolites, J. Catal., 1999,185,23-32. 

Bandow H, WashidaN, Akimoto H. 1985. Ring-cleavage reactions of aromatic hydrocarbons studied by FT-IR spectroscopy I. Photooxidation of toluene and benzene in the NOx-Air System. Bull Chem Soc Jpn 58 2531-2540. 

Other reactions of aromatic hydrocarbon anion radicals and amine cation radicals lead to exciplex emission, particularly in nonpolar solvents [15], Luminescence from exciplexes is most definitively observed in systems for which the redox reaction is energetically unable to yield a localized excited state. The free energy of exciplex formation, jE exc, is associated with solvation and geometry optimization in the encounter complex of and A+. 

While electron-transfer reactions of aromatic hydrocarbons are in general reactions of the state, electron transfer in carbonyl compounds can... 

Bisarene cations of Cr, Mo, and W are best synthesized by the reaction of aromatic hydrocarbon, metal halide, aluminum trihalide and aluminum metal at elevated temperature. Aromatic hydrocarbons, such as benzene, toluene, mesitylene, and hexamethylbenzene have been employed (Table III). The method is not applicable, however, when the aromatic hydrocarbon is itself reactive under Friedel-Crafts conditions. The bisarene cations are readily reduced to the neutral compounds by aqueous dithionite or, in the case of Mo and W, by alkaline disproportionation, e.g. 152),... 

Several modifications of the aluminum method are known. The cation [(MeCeHg)2Cr] has been prepared by the reduction of Cr(acac)3 with R3AI (R = Et, i-Bu) or (i-Bu)2A1H in toluene 333). Bisarene cation complexes of Cr, Mo, and W have been prepared directly by the reaction of aromatic hydrocarbon, AICI3, HCl, and the metal powder 70). 

The V-Ti-0 system has been extensively studied in connection with catalytic oxidation and ammoxidation reactions of aromatic hydrocarbons. Two principally different types of catalysts can be distinguished. One type of catalyst is prepared by impregnation, precipitation or mixing of the vanadium and titanium phases followed by calcination in air below the melting point of V. (1-4). The simultaneous reduction of V 0- and transformation of iiO (anatase) into rutile when heating below the V O melting point has been demonstrated to be due to topotactic reactions ( ). The formation of lower vanadium oxides can be of importance, because it has been found that reduced phases determine the activity and selectivity of catalysts (6,7). 

Highly ordered mesoporous mono- and bi-metallic incorporated catalysts with high porosity and surfece area are very active and selective in oxidation reaction of aromatic hydrocarbons such as styrene and benzene. Their framework composition can be modified by incorporation of various transition metals in the single or associated forms. The ordered hexagonal arrangement, the morphology, the surface area, and the catalytic activity and selectivity can be modified by method of the synthesis, nature and content of the metal and the molar ratio of the metals. Very active catalysts were obtained by incorporation of chromium and nickel in the hexagonal ordered structure. 

Bandow, H. and N. Washida Ring-Cleavage Reactions of Aromatic-Hydrocarbons Studied by Ft-Ir Spectroscopy. 2. Photooxidation of Ortho-Xylenes, Meta-Xylenes, and Para-Xylenes in the Nox-Air System, Bulletin of the Chemical Society of Japan, 58 (1985a) 2541-2548. 

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