Diphenyl ether degradation

Pfeifer F, S Schacht, J Klein, HG Trtiper (1989) Degradation of diphenyl ether by Pseudomonas cepacia. Arch Microbiol 152 515-519. 

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. 

The diphenyl ether herbicides are nonvolatile compounds, generally very lipophilic and insoluble in water. Solubility in water and octanol-water partition coefficients (logXow) of the various diphenyl ether herbicides range from 120mgL (acifluorfen) to 0.16 mg (oxyfluorfen) and from 2.9 (fomesafen) to 5.4 (acifluorfen), respectively. Diphenyl ether herbicides are stable in an acidic or alkaline condition, but some compounds are gradually degraded under the sunlight. ... 

Keywords Biological degradation, Cytochrome P450, Hydroxylation reaction, Polybrominated diphenyl ether, Trametes versicolor... 

Regarding the degradation of PBDEs by white-rot fungi, the first evidence of their ability to degrade a PBDE compound corresponds to a study published by Hundt et al. [27], which studied the degradation of 4-bromo-BDE by Trametes versicolor. The degradation occurs initially by hydroxylation reaction with the possible formation of three different isomers of hydroxy-diphenyl ether followed... 

The second compound important for the structural determination of chaenorhine (171) was obtained from A A -dimethylchaenorhine by Hofmann degradation. The resulting Hofmann base 174 was hydrogenated catalytically to the tetrahydro compound 177. Next, it was hydrolyzed in the presence of base and the product esterified with diazomethane. 6-Methoxy-diphenyl ether (3,4 -/ ,/ -dipropionic acid dimethyl ester) (178), which could be identified by comparison with a synthetic product, was obtained in a yield of 40% (see Scheme 32). 

Polychlorinated diphenyl ethers (PCDE) are common impurities in chlorophenol formulations, which were earlier used as fungicides, slimicides, and as wood preservatives. PCDEs are structurally and by physical properties similar to polychlorinated biphenyls (PCB). They have low water solubility and are lipophilic. PCDEs are quite resistant to degradation and are persistent in the environment. In the aquatic environment, PCDEs bioaccumulate. These compounds are found in sediment, mussel, fish, bird, and seal. PCDEs show biomagnification potential, since levels of PCDEs increase in species at higher trophic levels. PCDEs are also detected in human tissue. Despite the persistence and bio accumulation, the significance of PCDEs as environmental contaminants is uncertain. The acute toxicity and Ah-receptor-me-diated (aryl hydrocarbon) activity of PCDEs is low compared to those of polychlorinated di-benzo-p-dioxins (PCDD) and dibenzofurans (PCDF). Due to structural similarity to thyroid hormone, PCDEs could bind to thyroid hormone receptor and alter thyroid function. Furthermore, PCDEs might be metabolized to toxic metabolites. In the environment, it is possible that photolysis converts PCDEs to toxic PCDDs and PCDFs. 

Pyrolysis of acid azides results in the loss of nitrogen gas and intramolecular rearrangement of an R radical from carbon to nitrogen. Degradation to the isocyanate is best carried out by warming the azide in a solution of benzene, toluene, or diphenyl ether. Kinetic... 

The structure of the diphenyl ether moiety of 0-methylthalicberine was determined by degradation. 0-Methylthalicberine dimethochloride was converted through the Hofmann elimination reaction to a methine base (CVII) which was oxidized with permanganate to an acid identified as 2-methoxy-5,4 -dicarboxydiphenyl ether (XVIII) (81). 

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