Pentachlorophenol decomposition

X. T. Liu et al.. Simultaneous pentachlorophenol decomposition and granular activated carbon regeneration assisted by microwave irradiation. Carbon, 42, 415-422 (2004). 

Work by Boule et a. (21, 22) and Wong and Crosby (23) have provided information on the photodecomposition products of chlorophe-nols. In the case of pentachlorophenol degradation products included tetrachlorophenols, trichlorophenols, chlorinated dihydroxy benzenes, and nonaromatic fragments such as dichloromaleic acid (23). Other than CO2 which came from photo-mineralization, we did not attempt to identify the products of pentachlorophenol decomposition in our experiments. Boule (22) found that 2,4-dichlorophenol... 

In summary thermal decomposition of chlorinated phenols does not generally lead to dioxins. There are, however, several conditions which by themselves or combined would favor dioxin formation. First, of all chlorinated phenols either in bulk or in solution, only pentachlorophenol produced measurable amounts of dioxin. Secondly (Table II), only sodium salts in salid state reactions produced dioxins in reasonable yields. In contrast, the silver salt of pentachlorophenol (Figure 8) undergoes an exothermic decomposition at considerably lower temperatures and produced only higher condensed materials. No dioxin was detected. 

Rott B, S Nitz, F Korte (1979) Microbial decomposition of sodium pentachlorophenolate. 7 Agnc Food Chem 27 306-310. 

The role of N-sulfonyloxy arylamines as ultimate carcinogens appears to be limited. For N-hydroxy-2-naphthylamine, conversion by rat hepatic sulfotransferase to a N-sulfonyloxy metabolite results primarily in decomposition to 2-amino-l-naphthol and 1-sulfonyloxy-2-naphthylamine which are also major urinary metabolites and reaction with added nucleophiles is very low, which suggests an overall detoxification process (9,17). However, for 4-aminoazobenzene and N-hydroxy-AAF, which are potent hepatocarcinogens in the newborn mouse, evidence has been presented that strongly implicates their N-sulfonyloxy arylamine esters as ultimate hepatocarcinogens in this species (10,104). This includes the inhibition of arylamine-DNA adduct formation and tumorigenesis by the sulfotransferase inhibitor pentachlorophenol, the reduced tumor incidence in brachymorphic mice that are deficient in PAPS biosynthesis (10,115), and the relatively low O-acetyltransferase activity of mouse liver for N-hydroxy-4-aminoazobenzene and N-OH-AF (7,114,115). 

Pentachlorophenol applied to beech forest soils every 2 months for 2 years at the rate of 1.0 g/m2 markedly reduced populations of soil organisms. At 5.0 g/m2, it drastically reduced most of the soil animal species and also the microflora (Zietz et al. 1987). Reduction of the soil metabolism by PCP retards decomposition and affects the overall nutrient balance of forest ecosystems (Zietz et al. 1987). Pentachlorophenol is more toxic to earthworms in soils with comparatively low levels of organic materials. The LC50 (14-day) value for Lumbricus rubellus was 1094 mg PCP/kg DW soils with 6.1% organic matter, and 883 mg/kg DW soils with 3.7% organic matter (Van Gestel and Ma 1988). The earthworm Eisenia fetida andrei is more sensitive than Lumbricus rubellus ... 

Photochemical decomposition can also be carried out in the presence of a suspension of photoactive material such as Ti02 where substrate absorption onto the uv activated surface can initiate chemical reactions e. g. the oxidation of sulphides to sul-phones and sulphoxides [37]. This technology has been adapted to the destruction of polychlorobiphenyls (PCB s) in wastewater and is of considerable interest in environmental protection. Using pentachlorophenol as a model substrate in the presence of 0.2 % TiOj uv irradiation is relatively efficient in dechlorination (Tab. 4.5) [38]. When ultrasound is used in conjunction with photolysis, dechlorination is dramatically improved. This improvement is the result of three mechanical effects of sonochemistry namely surface cleaning, particle size reduction and increased mass transport to the powder surface. 

Photodecomposition of pentachlorophenol was observed when an aqueous solution was exposed to sunlight for 10 d. The violet-colored solution contained 3,4,5-trichloro-6-(2 -hydroxy-3, 4, 5, 6 -tetrachlorophenoxy)-o-benzoquinone as the major product. Minor photo-decomposition products (% yield) included tetrachlororesorcinol (0.10%), 2,5-dichloro-3-hydroxy-6-pentachloro-phenoxy-p-benzoquinone (0.16%), and 3,5-dichloro-2-hydroxy-5-2, 4, 5, 6 -tetrachloro-3-hy-droxyphenoxy-p-benzoquinone (0.08%) (Plimmer, 1970). 

This technology can remove oily sludges, pesticides, herbicides, pentachlorophenol, polychlorinated biphenyls (PCBs), coal by-products, wood treating compounds, dioxins, and furans. It is often used in conjunction with the company s base-catalyzed decomposition (BCD) process. The BCD process is designed to treat chlorinated compounds. 

De Ruiter et al. [4] observed that photochemical decomposition by ultraviolet irradiation of dansyl derivatives of chlorinated phenolic compounds in methanol-water mixtures led to the formation of highly fluorescent dansyl-OH and dansyl-OH3 species. The optimal irradiation time was 5.5s. This reaction was utilised in a post-column photochemical reactor in the high performance liquid chromatography determination of highly chlorinated phenols in river water. The method calibration curve (for dansylated pentachlorophenol) was linear over three orders of magnitude. 

Ide, A., Niki, Y., Sakamoto, F., Watanabe, I. (1972) Decomposition of pentachlorophenol in paddy soil. Agric. Biol. Chem. 36, 1937-1944. 

The simultaneous decomposition of pentachlorophenol and regeneration of activated carbon, using microwaves was reported [46], claiming that the quality of the carbon was maintained or actually increased after several adsorption/microwave-regeneration cycles. Carbon, in graphite form, has also been used as a microwave absorbent for the microwave pyrolysis of urea [47]. 

Possible mechanisms for the degradation of pentachlorophenol by Pseudomonas sp. (Adapted from Rochkind, M.L., J.W. Blackburn, and G.S. Sayler. 1986. Microbial Decomposition of Chlorinated Aromatic Compounds. EPA/600/2-86/090.)... 

This technique, however, was less than satisfactory. The polymeric acid chlorides were very sensitive to hydrolysis and polymer degradation occurred, presumably due to the presence of HCl. This decomposition was reflected by a decrease in viscosity during this reaction sequence. Furthermore, the final polymers exhibited strong, broad hydroxyl stretching bands in their IR spectra. Transesterification was also attempted unsuccessfully. Poly(ethyl acrylate) was reacted with pentachlorophenol in the presence of p-toluene sulfonic acid in benzene. Very little ethanol was Isolated and upon precipitation of the polymer in petroleum ether only oily material remained. 

Pentachlorophenol is a colorless to light or dark brown crystalline solid or powder with a weak or phenolie odor, but a strong, pungent odor when hot. It melts at between 187 and 189°C and boils with decomposition at 310°C. The odor threshold in water is 1.6 mg/L and the taste threshold in water is 30 /ig/L. It is soluble in aleohol, ether, benzene, and slightly soluble in water. It is stable at room temperature, in elosed eontainers, and under normal conditions. Photodegradation can occur in sunlight. It is also available as sodium penta-chlorophenate. 

The decomposition of pinacyanol chloride dye using octahedral layered mixed-valent manganese oxides has been published [81]. Catalytic reduction reactions using birnessite have been tried for removing pentachlorophenol (PCP) from soil and water (detoxyfication) [82]. Transformation and dechlorination of PCP incubated with peroxidase, laccase, or birnessite is decreased in the presence of humic monomers as cosubstrate. The dehalogenation number for birnessite is 3.3, compared with 3.5 for peroxidase and 1.5 for laccase [82]. 

Pentachlorophenol is toxic, the decomposition rate in nature is slow, it is lipophilic and therefore liable for bioaccumulation. The use of pentachlorophenol and its salts (e.g. as wood preservation agent) is drastically restricted or banned in many industrialized countries by law, so the open use since 1976 in Europe and since 1979 in the United States, and total stop of the use since 1985 in Europe. 

The other example, a polymer-bound fungicide, is found in the copolymerization of pentachlorophenyl acrylate with vinyl acetate and ethyl acrylate. This pentachlorophenol-based product could have use as an anti-fouling agent in marine coatings. In this case it was necessary to copolymerize with ethyl acrylate. The homopolymer was found to be too hydrophobic to allow decomposition of the polymer and allow release of the active agent in sufficiently high concentrations to have the appropriate biocide effect. 

The decomposition of benzene and naphthalene and its homologues by microorganisms has already been discussed earlier. The metabolizing mechanisms of naphthalenes in fish have been well studied [47, 49]. Decomposition products of chlorobenzene in daphnia, mosquitos, snails and fishes are the polar compounds chlorophenol and chloro-o-dihydroxybenzene amongst other compounds, those of nitrobenzene aniline, acetanilide, aminophenols and nitrophenols and those of hexachlorobenzene pentachlorophenol and unknown compounds [71]. Bromoben-zene is deactivated to the toxic bromophenol [217]. In the case of man and land mammals, studies have concentrated on the metabolism of benzene, toluene, xylenes and styrene, which are also significant in occupational medicine [12, 13, 136, 195, 196, 215-217], A comparison of the metabolism of benzene into phenol in various animal species with the aid of microsomal preparations of the lungs or liver yielded vast differences. However, it is possible for benzene, in part, to inhibit or prevent its own metabolism [218]. 

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