4- Chlorophenol, photochemical

Pandiyan, T, Martinez, R., Orozco Martinez, J., Burillo Amezcua, G., and Martinez-Carrillo, M.A., Comparison of methods for the photochemical degradation of chlorophenols, /. Photochem. Pho-tobiol. A Chem., 146,149-155, 2002. 

The objectives of the soil persistence experiments were (1) to learn the effect of soil type and concentration on the TCDD degradation rate, (2) to isolate and characterize degradation products from DCDD and TCDD, and (3) to determine whether chlorodioxins could be formed from chlorophenol condensation in the soil environment. This last study was essential since quality control at the manufacturing level could reduce or eliminate the formed dioxin impurity. But the biosynthesis of chlorodioxins by chlorophenol condensation in the soil environment could not be controlled and would have connotations for all chlorophenol-de-rived pesticides if formation did occur. The same question needed to be answered for photochemical condensation reactions leading to chloro-... 

It has been shown that a combination of photolytic and biotic reactions can result in enhanced degradation of xenobiotics in municipal treatment systems, for example, of chlorophenols (Miller et al. 1988a) and benzo[a]pyrene (Miller et al. 1988b). Two examples illustrate the success of a combination of microbial and photochemical reactions in accomplishing the degradation of widely different xenobiotics in natural ecosystems. Both of them involved marine bacteria, and it therefore seems plausible to assume that such processes might be especially important in warm-water marine enviromnents. 

PCDDs are present as trace impurities in some commercial herbicides and chlorophenols. They can be formed as a result of photochemical and thermal reactions in fly ash and other incineration products. Their presence in manufactured chemicals and industrial wastes is neither intentional nor desired. The chemical and environmental stability of PCDDs, coupled with their potential to accumulate in fat, has resulted in their detection throughout the global ecosystem. The number of chlorine atoms in PCDDs can vary between one and eight to produce up to 75 positional isomers. Some of these isomers are extremely toxic, while others are believed to be relatively innocuous. 

Werkhoven-Goewie, C.E., Boon, W.M., Praat, A.J.J., Frei, R.W., Brinkman, U.A. Th., and Little, C.J., Preconcentration and LC analysis of chlorophenols, using a styrene-divinyl-benzene copolymeric sorbent and photochemical reaction detection, Chromatographia, 16, 53, 1982. 

Mills, A. Morris, S. Davies, R. Photomineralisation of 4-chlorophenol sensitised by titanium dioxide A study of the intermediates, J. Photochem Photobiol. 1993, A70, 183. 

Serpone, N. Maruthamuthu, P. Pichat, P. Pelizzetti, E. Hidaka, H. Exploiting the interparticle electron transfer process in the photocatalyzed oxidation of phenol, 4-chlorophenol and pentachlorophenol Chemical evidence for electron and hole transfer between coupled semiconductors, J. Photochem. Photobiol., A Chem. 1995, 85, 247. 

Kang MG, Han H-E, Kim K-J. Enhanced photodecomposition of 4-chlorophenol in aqueous solution by deposition of CdS on Ti02. J Photochem Photobiol A Chem 1999 125 119-25. 

Some of the topics addressed here have been reviewed by other authors. Studies of photoinduced processes (direct or indirect) of chlorophenols carried out before 1998 have been covered comprehensively [8] this work will only cursorily be treated here. A detailed overview of the photochemical behavior of phenylurea herbicides was in press at the time of writing this article [9]. The related subject of the photodegradation of pharmaceuticals in the aquatic environment has been reviewed very recently [10]. 

Jakob L, Hashem T, Burki S, Guindy NM, Braun AM (1993) Vacuum-Ultraviolet (VUV) Photolysis of Water Oxidative Degradation of 4-Chlorophenol, J. Photochem. Photobiol. A Chem. 75 97-103. 

Mills, A., and Morris, S. Photomineralization of 4-chlorophenol sensitized by titanium dioxide A study of the initial kinetics of carbon dioxide photogeneration . /. Photochem. Photobiol. A. 71, 75 (1993). 

This concentration dependence is illustrated for the photochemical oxidation of 4-chlorophenol on Ti02 particles (Figure 12.13). 

Figure 12.13. Photochemical oxidation of 4-chlorophenol on Ti02 particles. The oxidation rate as a function of dissolved 4-chlorophenol follows a Langmuir adsorption isotherm and reflects the surface concentrations. (From Al-Ekabi et al., 1989.)...

A charge transfer complex is involved in the photochemical reaction between 4-cresol and tetranitromethane. Irradiation at 350 nm yields the o-nitrated product 235 ° . Other phenols such as phenol, 2- and 4-chlorophenol and 2- and 4-cresol behave in a similar manner and irradiation yields 2- and 4-nitrated products (236, 237) ° . The quantum yields for product formation are in the range 0.12-0.31. Only the formation of 3-nitrophenol from phenol is inhibited, as might be expected from attack at the 3-position, and shows a low quantum yield. It has been reported that 2-hydroxy- or 4-hydroxybiphenyl and 4,4 -dihydroxybiphenyl are the primary products formed from the photochemical reaction of biphenyl with sodium nitrate in aqueous methanol . Apparently the hydroxybiphenyls are prone to undergo photochemical nitration as a secondary process and yield the biphenyls 238 and 239 as well as 4,4 -dihydroxy-3,3 -dinitrobiphenyl, originally reported by Suzuki and coworkers under heterogeneous conditions. 

Carbene formation was mentioned in an earlier section. This elimination of HCl from 4-chlorophenol or elimination of other hydrogen halides from halophenols could have been inferred from earlier photochemical studies on this and other derivatives. Boule and his coworkers irradiated 4-chlorophenol under deoxygenated conditions and obtained the corresponding quinhydrone and the 2,4 -dihydroxy-5-chlorobiphenyl °. Other research demonstrated that its irradiation in neutral aqueous solutions gave the corresponding quinone " and also that de-aeration did not seem to affect the reaction. ... 

Chlorophenol is also reactive and irradiation in water leads to its conversion into resorcinoP" or in methanol to yield 3-methoxyphenol in 94% yield. Photoamidation with N-methylacetamide of 3-chlorophenol is also efficient and resnlts in the formation of the phenol 241 in a yield of 77%. Intramolecnlar amidation arises on irradiation of 242 in basic methanol. This resnlts in the formation of the indole derivative 243 as well as the methoxylated prodnct 244. More complex halophenols such as 245 are also photochemically reactive, but this yields a complex mixture of products including a benzofuran. The formation of this must be similar to the cychzations described earlier and involves the attack of a radical, produced by the C—I bond fission, on the other ring . 3-Nitrophenol is converted on irradiation in aqueous solution into a variety of products such as nitrocatechols, nitroresorcinol and resorcinol itself... 

Mills, A., Morris, S., Photomineralization of 4 Chlorophenol Sensitized by Titanium Dioxide A Study of the Initial Kinetics of Carbon Dioxide Photogeneration, J. Photochem. Photobiol. A 1993, 71, 75 83. 

Literature on this subject tells that chlorophenols cause these unwanted byproducts to form (refs. 4, 5, 6) when exposed to thermal, photochemical or basic conditions (eqn. 1). 

PROBABLE FATE photolysis, based on data for 4-chlorophenol, intramolecular photolysis may be a very important fate, reaction with photochemically produced hydroxyl radicals has a half-life of 1.1 days, will degrade through photolysis if released to water oxidation can occur, but probably cannot compete with biodegradation hydrolysis not important volatilization not important sorption data inconclusive, but potential for adsorption by organics exists biological processes no data on bioaccumulation, biodegradation data not applicable to environment other reactions/interactions can be chlorinated further by chlorine present in HiO... 

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