Photolysis of pentachlorophenol

Pignatello JJ, MM Martinson, JG Steiert, RE Carlson, RL Crawford (1983) Biodegradation and photolysis of pentachlorophenol in artificial freshwater streams. Appl Environ Microbiol 46 1024-1031. 

Lamparski, L.L., R.H. Stehl, and R.L. Johnson. 1980. Photolysis of pentachlorophenol-treated wood. Chlorinated dibenzo-p-dioxin formation. Environ. Sci. Technol. 14 196-200. 

Wong, A.S. and D.G. Crosby. 1978. Photolysis of pentachlorophenol in water. Pages 119-25 in K.R. Rao (ed.). Pentachlorophenol Chemistry, Pharmacology, and Environmental Toxicology. Plenum Press, New York. 

Donaldson, S.G. and Miller, G.C. Transport and photolysis of pentachlorophenol in soils subject to evaporating water. J. Environ. Qual, 26(2) 402-409, 1997. 

Lamparski LL, Stehl RJ, Johnson RL. 1979b. Photolysis of pentachlorophenol-treated wood ... 

Liu, P.Y., Zheng, M.H. and Xu, X.B. (2002) Phototransformation of polychlorinated dibenzo-p-dioxins from photolysis of pentachlorophenol on soils surface. Chemosphere 46, 1191-1193. 

Vollmuth S, Zajc A, Niessner R (1994), Environ. Sci. Technol. 28 1145-1149.. .Formation of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans during photolysis of pentachlorophenol-containing water"... 

An interesting result has been obtained in a study of the dechlorination of polychlorobenzenes by direct irradiation in acetonitrile in addition to dechlorination, products resulting from rearrangement of the chlorine atoms to positions mefa to their original point of attachment are observed. Thus orfho-dichlorobenzene was found to yield mainly chlorobenzene along with small amounts of para-dichlorobenzene the authors speculate that the rearrangement products are formed by recombination of an aryl-chlorine radical pair. In another novel result photolysis of pentachlorophenol in acetonitrile is found to give small amounts of the benzoxazole (160). ... 

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. 

Tab. 4.5. Photolysis of aqueous pentachlorophenol (2.4x10 M) containing 0.2% Ti02).

When an aqueous solution containing pentachlorophenol (45 pM) and a suspension of titanium dioxide (2 g/L) was irradiated with UV light, carbon dioxide and HCl formed in quantitative amounts. The half-life for this reaction at 45-50 °C is 8 min (Barbeni et al, 1985). When an aqueous solution containing pentachlorophenol was photooxidized by UV light at 90-95 °C, 25, 50, and 75% degraded to carbon dioxide after 31.7, 66.0, and 180.7 h, respectively (Knoevenagel and Himmelreich, 1976). The photolysis half-lives of pentachlorophenol under sunlight irradiation in distilled water and river water were 27 and 53 h, respectively (Mansour et al., 1989). 

P 15.5 Estimating the Direct Photolysis Half-Life of Pentachlorophenol in Chesapeake Bay (adaptedfrom Roberts, 1995)... 

The direct photolysis of nitrobenzene was found to be slow and it did not occur at a significant rate. The naphthalene/pentachlorophenol system showed that the degradation rate of each compound was affected by the presence of the other compounds. In addition, both compounds when subjected to direct photolysis produced significant amounts of hydrogen peroxide. Thus, shortly after the initiation of the photolysis, the system became a UV/H202 process. 

Figure 10. Proton-nmr spectra recorded (A) before and (D) during tne photolysis of 4-phenylacetophenone and pentachlorophenol in isopropanol. The methyl protons spectrum at 6 2.0 was recorded at a much lower sensitivity than that of the aromatic protons at...

Preservatives Pentachlorophenol (PCP) Phenols, quinones, acids, C02, CD Initiated by direct photolysis of PCP Complex... 

Photolysis of various chlorophenols as a function of time are shown in Fig. 1. The photo-transformation and photo-mineralization of the compounds followed a first-order equation In (Cg /C) kpt, where Cg and C are the concentrations of the compound at time zero and time t, while kp is the first-order photolysis rate constant. The photolysis half-lives of the compounds were calculated using the equation ti/2 = 0.693/kp. The relative rates of photolysis in estuarine water decreased in tne order 2,4,5-trichlorophenol, 2,4-dichlorophenol, pentachlorophenol, p-chlorophenol, phenol (Table 1). 

Our studies indicated rapid photolysis of trichlorophenol, di-chlorophenol, and pentachlorophenol in both distilled and estuarine water. We can compare our results of pentachlorophenol with those of other investigators who have studied the photolysis of this compound in both fresh and marine waters O, 17-20). The photolysis rate constant kp for pentachlorophenol in a freshwater stream was 0.29 hr ( 1/2 2.4 hr) at 3.8 cm in the summer ( W), while we found a kp of 0.37 hr ( 1/2 " 2 hr, light hours) at a depth of 3.0 cm in the summer (Table I). The half-life of pentachlorophenol in a 1 m deep freshwater pond was 1.5 to 3 days (17) while in 5.5 m deep marine mesocosm the half-life was 22 days (18). Using lamps to simulate sunlight the pentachlorophenol in surface seawater was found to have a half-life of 2.4 hr. ( 5), Thus our rate constant and half-life for pentachlorophenol photolysis was similar to one determined by others in surface waters. Due to attenuation of light by substances in the water longer half-lives, i.e., days rather than hours, are found for pentachlorophenol when distributed throughout the water column. 

An important aspect of our studies were the effect of cloud cover, pH, chloride ion, and season on the photolysis of phenol and various chlorophenols. The effect of pH on the photolysis of chlorophenols is due to the higher rate of photolysis of the phenoxlde ion relative to the nonionized compound, due to stronger absorbance by the phenoxide ion ( ). The pK of dichlorophenol, trichlorophenol, and pentachlorophenol are 7.6, 7.0 and 4.8, respectively (.22, 24). Low photolysis rates of chlorophenols in both estuarine and distilled water were obtained at pH below the pK (Table III). At pH 7.6 found in estuarine water 50Z, 80Z, and 99.82 of the dichlorophenol, trichlorophenol, and pentachlorophenol, respectively, is in the form of the phenoxide ion. The photolysis rate of pentachlorophenol in estuarine water was lower than in distilled water (Table I). Addition of chloride ion to distilled water containing pentachlorophenol resulted in a decrease in the photolysis rate. Miille and Crosby ( 5) found that pentachlorophenol had a lower photolysis rate in seawater compared to distilled water due to the photonucleophilic... 

Figure 4. Computed depth dependence for the direct photolysis of trifluralln and pentachlorophenol In different water types (average rate constants parenthesized).

PCP presents a different picture from that of the lower chlorophenols and their derivatives. The corresponding dioxin shows much more stability to light than does TCDD, enough to permit its prolonged existence at low concentrations in a photoreactor. As a phenol it can directly yield dioxins, a process favored by its normal mode of application as the sodium salt. Although octachlorodibenzo-p-dioxin has much lower mammalian toxicity than TCDD (6), its formation, properties, and effects demand additional investigation. Technical preparations of PCP are frequently mixtures of tetra- and pentachlorophenols consequently, hepta-and possibly hexachlorodibenzo-p-dioxins might be expected as photolysis products in addition to the octachloro derivative. 

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