Chlorobenzene degradation

Photolytic. Under artificial sunlight, river water containing 2-5 ppm chlorobenzene degraded to phenol and chlorophenol. The lifetimes of chlorobenzene in distilled water and river water were 17.5 and 3.8 h, respectively (Mansour et al, 1989). In distilled water containing 1% acetonitrile exposed to artificial sunlight, 28% of chlorobenzene photolyzed to phenol, chloride ion, and acetanilide with reported product yields of 55, 112, and 2%, respectively (Dulin et al., 1986). 

Kunze, M., Zeilin, K.F, Retzlaff, A., Pohl, J.O. Schmidt, E., Janssen, D.B., Vilchez-Vargas, R., Pieper D.H., Walter, Reineke W. 2009. Degradation of chloroaromatics by Pseudomonas putida GJ31 assembled route for chlorobenzen degradation encoded by clusters on plasmid KWland the chromosome. Microbiology 155 4069-4083. 

FIGURE 3.22 Degradation involving dioxygenation via acyl chlorides of (a) chlorobenzene, (b) y- hexachlo-rocyclohexane, and (c) pentachlorophenol. 

Mars AE, T Kasberg, SR Kaschabek, MH van Agteren, DB Janssen, W Reineke (1997) Microbial degradation of chloroaromatics use of the mefa-cleavage pathway for mineralization of chlorobenzene. J Bacterial 179 4540-4537. 

Rapp P, KN Timmis (1999) Degradation of chlorobenzenes at nanomolar concentrations by Burkholderia sp. strain PS14 in liquid cultures and in soil. Appl Environ Microbiol 65 2547-2552. 

Sommer C, H Gorisch (1997) Enzymology of the degradation of (di)chlorobenzenes by Xanthobacter flavus 14pl. Arch Microbiol 167 384-391. 

Ralstonia eutropha (Alcaligenes eutrophus) strain NH9 is able to degrade 3-chlorobenzene by the modified ortho pathway. The cbnA gene that encodes 3-chlorocatechol-l, 2-dioxygenase was introduced into rice plants (Oryza sativa -p.japonicd) under the control of a virus 35S promoter. 3-Chlorocatechol induced dioxygenase activity in the callus of the plants, and leaf tissues oxidized 3-chlorocatechol with the production of 2-chloromuconate... 

The structural range of industrially important representatives of these groups is enormous, and includes chlorobenzenes (solvents), polychlorinated biphenyls (PCBs) (hydraulic and insulating fluids), and polybrominated biphenyls and diphenyl ethers (flame retardants). There is widespread concern over both the persistence and the potential toxicity of all these compounds, and sites that have become contaminated during their production represent a threat both to the environment and to human health. Pathways for the aerobic bacterial degradation of chlorobenzenes and chlorobiphe-nyls, and their brominated analogs have been discussed in Chapter 9, Part 1. 

Although the possibly incompatible pathways for the degradation of chlorobenzene and toluene has been noted, a strain of Ralstonia sp. from a site contaminated with chlorobenzene contained the genes for both chlorocatechol degradation and the dioxygenase system for the degradation of benzene/toluene (van der Meer et al. 1998). The evolution of this strain resulted in a natural lowering... 

Oxidation of polyalkenes is accompanied by the degradation of macromolecules [11,12,33-41,122,123]. Thus, when HDPE is oxidized in chlorobenzene to a concentration of hydroperoxyl groups of 0.12mol L 1 (378 K, 1 h) and 0.20mol L 1, the mean molecular weight of... 

This reaction is very exothermic (A// —180 to —200kJ mol-1) and, therefore, seems to be very probable from the thermochemical point of estimation. The pre-exponential factor is expected to be low due to the concentration of the energy on three bonds at the moment of TS formation (see Chapter 3). To demonstrate that this reaction is responsible for the oxidative destruction of polymers, PP and PE were oxidized in chlorobenzene with an initiator and analyzed for the rates of oxidation, destruction (viscosimetrically), and double bond formation (by the reaction with ozone) [131]. It was found that (i) polymer degradation and formation of double bonds occur concurrently with oxidation (ii) the rates of all three processes are proportional to v 1/2, (iii) independent of p02, and (iv) vs = vdbf in PE and vs = 1.6vdbf in PP (vdbf is the rate of double bond formation). Thus, the rates of destruction and formation of double bonds, as well as the kinetic parameters of these reactions, are close, which corroborates with the proposed mechanism of polymer destruction. Therefore, the rate of peroxyl macromolecules degradation obeys the kinetic equation ... 

The degradation of polystyrene in a chlorobenzene solution in the presence of dioxygen and initiator also occurs with the rate vs v [140,141], However, the vs/b ratio was found to be much less than unity. 

Recently Madras et al. [17], studying the degradation of styrene and poly(vinyl acetate) in chlorobenzene have analysed their data using a continuous distribution kinetics model. 

Soil Under aerobic conditions, indigenous microbes in contaminated soil produced pentachlorocyclohexane. However, under methanogenic conditions, a-BHC was converted to chlorobenzene, 3,5-dichlorophenol, and the tentatively identified compound 2,4,5-trichlorophenol (Bachmann et al., 1988). Manonmani et al. (2000) isolated a microbial consortium from sewage and soil that could completely mineralize a-BHC in 14 d at 30 °C. The acclimated consortium could degrade up to 100 mg/L of a-BHC within 72 h at a degradation rate of 58 mg/L-day. 

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