4- Phenoxyphenols

The most common use of 2-(2, 4 -dichlorophenoxy)-5-chlorophenol (2,4,4 -trichloro 2 -phenoxyphenol) is in the personal care products market, where it is commonly known as triclosan and is the active antibacterial in underarm deodorants. It has also found some acceptance as an antibacterial component of plastic mattress covers. 

Therefore, hplc methods seem more effective. By usiag a combiaed uv and electrochemical detection technique (52), the gem-chlotinated cyclohexadienones, the chlorophenols, and the phenoxyphenols present ia the chlorination mixtures can be determined with great accuracy. 

Thus, it seems that dioxins are only formed if the intermediate phenoxyphenol can be forced and held in a special molecular configuration to avoid the various competitive reactions leading to diflEerent products. 

Chlorinated dibenzo ip-dioxins are contaminants of phenol-based pesticides and may enter the environment where they are subject to the action of sunlight. Rate measurements showed that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is more rapidly photolyzed in methanol than octachlorodi-benzo-p-dioxin. Initially TCDD yields 2,3,7-trichlorodiben-zo-p-dioxin, and subsequent reductive dechlorination is accompanied by ring fission. Pure dibenzo-p-dioxin gave polymeric material and some 2,2 -dihydroxybiphenyl on irradiation. Riboflavin-sensitized photolysis of the potential precursors of dioxins, 2,4-dichlorophenol and 2,4,5-trichloro-phenol, in water gave no detectable dioxins. The products identified were chlorinated phenoxyphenols and dihydroxy-biphenyls. In contrast, aqueous alkaline solutions of purified pentachlorophenol gave traces of octachlorodibenzo-p-dioxin on irradiation. 

Light can effect the coupling of phenols. For example, Joschek and Miller (22) found that phenoxyphenols could be produced in the flash photolysis of phenol, but although sought, no dioxin was detected in the reaction products. 

The reaction products from 2,4-dichlorophenol were tetrachloro-phenoxyphenols and tetrachlorodihydroxybiphenyls (Figure 5), as determined from their mass spectra and those of their methyl ethers. 4,6-Dichloro-2-(2, 4 -dichlorophenoxy)phenol (V) was the major phenoxy-phenol the mass spectral fragmentation pattern of o-hydroxyphenol ethers is quite characteristic since a hydrogen transfer occurs during the fragmentation (Figure 6). A trace of a trichlorophenoxyphenol also was detected and was formed presumably by the unsensitized reductive loss of chlorine, discussed previously. 

TCP), and pentachlorophenol (PCP), in order of abundance. Minor amounts of other trichlorophenols and dichlorophenols may also be present, as well as recalcitrant polychlorinated phenoxyphenols (PCPPs) and PCDD/Fs as impurities [75, 76]. In Finland, approximately 30,000 tons of CP products were used between 1934 and 1988, when they were banned because of their potential toxicity to humans and the environment [77, 78]. The careless manufacturing and application of wood preservatives together with the lack of suitable waste disposal caused massive contamination of river sediments and sawmill sites. For example, the river Kymijoki in southern Finland was identified as the largest source of dioxins accumulating in fish in the entire Baltic area. Similar products were used in other European countries, especially Nordic countries with a large forestry industry, such as Sweden [79]. 

Several academic and pharmaceutical groups have conducted structure-based design and SAR studies around triclosan aiming at harvesting its potency without its biocidal component. Among the results of these efforts, CPP (24) was found to be sevenfold more tightly bound to E. coli Fabl than triclosan with an MIC value of 0.07 pg/mL, fourfold lower than that of triclosan [43]. Phenoxyphenol 25 is extremely potent... 

Commercial PCP preparations often contain variable amounts of chlorophenols, hexachloroben-zene, phenoxyphenols, dioxins, dibenzofurans, chlorinated diphenyl ethers, dihydroxybiphenyls, anisoles, catechols, and other chlorinated dibenzodioxin and dibenzofuran isomers. These contaminants contribute to the toxicity of PCP — sometimes significantly — although the full extent of their interactions with PCP and with each other in PCP formulations are unknown. Unless these contaminants are removed or sharply reduced in existing technical- and commercial-grade PCP formulations, efforts to establish sound PCP criteria for protection of natural resources may be hindered. 

Hamilton, S.J., L. Cleveland, L.M. Smith, J.A. Lebo, andF.L. Mayer. 1985. Toxicity of pure pentachlorophenol and chlorinated phenoxyphenol impurities to fathead minnows. Environ. Toxicol. Chem. 5 543-552. 

List of abbreviations BOD, biological oxygen demand CA, chloroanisol CCA, copper-chromate-arsenate CP, chlorophenol 2,4-D, dichlorophenoxyacetic acid DCP, dichlorophenol CFSTR, continuous-flow stirred tank reactor FBBR, fluidized-bed biofilm reactor MCP, monochlorophenol NAPL, non-aqueous phase liquid PAH, polycyclic aromatic hydrocarbon PCPP, polychlorinated phenoxyphenol PCDF, polychlorinated dibenzofuran PCDD, polychlorinated dibenzodioxin PCR, polymerase chain reaction PCP, pentachlorophenol PCA, pentachloroanisole TeCP, tetrachlorophenol TeCA, tetrachloroanisole TCC, trichlorocatechol TCP, trichlorophenol TOC, total organic carbon 2,4,5-T, trichlorophenoxyacetic acid UASB, upflow anaerobic sludge blanket reactor VSS, volatile suspended solids. 

Technical CP formulations contain impurities such as polychlorinated phenoxyphenols (PCPPs), polychlorinated dibenzodioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs) (Humppi et al., 1984 Kitunen et al., 1985 Jackson Bisson, 1990). Therefore, PCPPs, PCDFs, and PCDDs are often found in CP-contaminated wood treatment sites (Kitunen et al., 1985, 1987 Jackson Bisson, 1990 Kitunen Salkinoja-Salonen, 1990 Trudell et al., 1994). PCPP concentrations up to 78 mg/kg, PCDF up to 3-8 mg/kg, and PCDDs at 13 mg/kg have been detected in CP-contaminated sites (Kitunen et al., 1987 Jackson Bisson, 1990). 

Humppi, T., Knuutinen, J. Paasivirta, J. (1984). Analysis of polychlorinated phenoxyphenols in technical chlorophenol formulations and in sawmill environment. Chemosphere, 11, 1235-41. 

Kitunen, V. H., Valo, R.J. Salkinoja-Salonen, M. S. (1985). Analysis of chlorinated phenols, phenoxyphenols and dibenzofurans around wood preserving facilities. International Journal of Environmental and Analytical Chemistry, 20, 13-20. 

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