Polynuclear aromatics, oxidation

Aerobic, Anaerobic, and Combined Systems. The vast majority of in situ bioremediations ate conducted under aerobic conditions because most organics can be degraded aerobically and more rapidly than under anaerobic conditions. Some synthetic chemicals are highly resistant to aerobic biodegradation, such as highly oxidized, chlorinated hydrocarbons and polynuclear aromatic hydrocarbons (PAHs). Examples of such compounds are tetrachloroethylene, TCE, benzo(a)pyrene [50-32-8] PCBs, and pesticides. 

Benzene monoxide-oxepin and its sulfur analog are treated elsewhere (Chapter 5.1.7) (67AG(E)385). However, we point out here that electron-withdrawing substituents often favor the benzene oxide tautomer. The first study on oxides of the environmentally hazardous polychloro- and polybromo-biphenyls shows that they exist mainly in the benzene oxide form (81JOC3721). Oxides of polynuclear aromatic hydrocarbons (PAH) also exist mainly in the fused-ring oxirane form. 

Katz, M., Chan, C., Tosine, H., Sakuma, T. (1979) Relative rates of photochemical and biological oxidation (in vitro) of polynuclear aromatic hydrocarbons. In Polynuclear Aromatic Hydrocarbons. Jones, P.W., Leher, P., Eds., pp. 171-189, Ann Arbor Science Publishers, Ann Arbor, MI. 

The most commonplace substrates in energy-transfer analytical CL methods are aryl oxalates such as to(2,4,6-trichlorophenyl) oxalate (TCPO) and z s(2,4-dinitrophenyl) oxalate (DNPO), which are oxidized with hydrogen peroxide [7, 8], In this process, which is known as the peroxyoxalate-CL (PO-CL) reaction, the fluorophore analyte is a native or derivatized fluorescent organic substance such as a polynuclear aromatic hydrocarbon, dansylamino acid, carboxylic acid, phenothiazine, or catecholamines, for example. The mechanism of the reaction between aryl oxalates and hydrogen peroxide is believed to generate dioxetane-l,2-dione, which may itself decompose to yield an excited-state species. Its interaction with a suitable fluorophore results in energy transfer to the fluorophore, and the subsequent emission can be exploited to develop analytical CL-based determinations. 

Polynuclear aromatic hydrocarbons can be oxidized photolytically with the formation of cyclic peroxide. For example, anthracene is photooxidized to peroxide with the quantum yield 0 = 1.0 [205], The introduction of quenchers lowers the peroxide yield. 

Kirso, U., L. Belykh, D. Stom, N. Irha, and E. Urbas. 1983. Oxidation of benzo[a]pyrene by plant enzymes. Pages 679-687 in M. Cooke and A.J. Dennis (eds.). Polynuclear Aromatic Hydrocarbons Mechanisms, Methods and Metabolism. Battelle Press, Columbus, OH. 

The Biolift reactor has been used to treat soils contaminated with benzene, toluene, ethylbenzene, and xylene (BTEX), total petroleum hydrocarbons (TPHs), and polynuclear aromatic hydrocarbons (PAHs). The process uses microorganisms to oxidize organic compounds, yielding innocuous by-products. 

Relative Rates of Photochemical and Biological Oxidation (in vitro) of Polynuclear Aromatic Hydrocarbons," in POLYNUCLEAR AROMATIC HYDROCARBONS, P.W. Jones and P. Leber (Editors), Ann Arbor Science Publishers, Inc., Ann Arbor, MI, 171-89. 

Oxidation to Quinones. Direct oxidation of arenes to quinones can be accom-plished by a number of reagents. Very little is known, however, about the mechanism of these oxidations. Benzene exhibits very low reactivity, and its alkyl-substituted derivatives undergo benzylic oxidation. Electrochemical methods appear to be promising in the production of p-benzoquinone.797 In contrast, polynuclear aromatic compounds are readily converted to the corresponding quinones. 

Polynuclear aromatics that cannot form K-region epoxides such as anthracene may be oxidized to the corresponding quinones806 by these reagents. Others, such as naphthalene and triphenylene, may be converted to polyepoxides under carefully controlled reaction conditions and workup procedures.808,809... 

Photolysis, in the presence of oxygen, of alkenes containing an ally lie hydrogen atom leads to the formation of hydroperoxides. The sensitized process is more efficient, and often yields photoproducts different in structure from those obtained by nonsensitized photooxidation. Cyclohexadiene and related dienes on photolysis in the presence of oxygen yield the transannular peroxides. Thus, on photosensitized oxidation, a-terpinene (410) is converted into ascaridole (411).435 The equivalent process is not, in general, observed in acyclic dienes. Certain polynuclear aromatic hydrocarbons, such as anthracene and naphthacene and including the heterocycles 5,10-diphenyl-1-... 

Polynuclear aromatic compounds such as naphthalene or anthracene are oxidized by chromyl reagents mainly into quinones, with a significant NIH shift, providing evidence for the intermediacy of arene oxide intermediates.306,54... 

Polynuclear aromatic hydrocarbons are oxidatively cleaved by Ru04 under mild conditions, and this reaction can be performed catalytically in the presence of NaOCl (equation 120).336... 

Beltran et al. (1996a) investigated the advanced oxidation of the aqueous solution of three polynuclear aromatic hydrocarbons (PAHs) fluorene, phenanthrene, and acenaphthene. The oxidative mechanism of substrates by 03 alone, 03 combined with H202, UV radiation (254 nm) alone, or a combination of UV/H202 has been analyzed. In addition, the influence of different water sources, such as surface and organic-free waters, and type of occurring oxidation was also studied. 

Beltran, F.J., Ovejero, G., and Rivas, J., Oxidation of polynuclear aromatic hydrocarbons in water, Indust. Eng. Chem. Res., 35, 883-890, 1996a. 

Beltran, F.J., Gonzalez, M., and Rivas, F.J., Advanced oxidation of polynuclear aromatic hydrocarbons in natural waters, /. Environ. Sci. Health, A31(9), 2193-2210, 1996b. 

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