Chlorine, photodecomposition

The degradation of mirex in water occurs primarily by photolysis. During the photodecomposition of mirex, the chlorine atoms are replaced by hydrogen atoms. The primary photoreduction product of... 

Karpel Vel Leitner N, De Laat J, Dore M. 1992. Photodecomposition of chlorine dioxide and chlorite by UV-irradiation- part II. Kinetic study. Water Res 26(12) 1665-1672. 

Zika RG, Moore CA, Gidel LT, et al. 1984. Sunlight-induced photodecomposition of chlorine dioxide. In Jolley RL, Bull RJ, Davis WP, et al, eds. Water chlorination-Chemistry, environmental impact and health effects. Vol. 5. Williamsburg, VA Lewis Publishers, Inc. 

Chlorine atoms and other chlorine species formed by photodecomposition of carbon tetrachloride in the stratosphere can catalyze reactions that destroy ozone. As the manufacture of carbon tetrachloride for use in chlorofluorocarbons is phased out according to a recent international agreement (EPA 1987e), the impact of carbon tetrachloride on atmospheric ozone is likely to decrease. 

The presence of chlorine atoms in the ketone molecule leads to a further complication, since the C-Cl bond dissociation energy may be of the order of 80 kcal. mol.-1, so that a photodecomposition of type C becomes energetically feasible. 

The simplest change which may be made in the acetone molecule is the substitution of a hydrogen atom by chlorine, yet this slight alteration leads to a very profound change in the pattern of photodecomposition. 

Decomposition experiments for these CPs listed in Table 14.11 were carried out by the simultaneous action of UV radiation and Fenton s reagent (Benitez et al., 2000). Table 14.11 shows the first-order rate constants and half-lives. During the photo-Fenton s reagent reaction, the single photodecomposition rate constant, ku decreased as the number of chlorine substituents increased. In addition, combined rate constants, ku are much greater than the radical reaction constants, k,. Therefore, this confirms the additional contribution of the radical reaction due to generation of the hydroxyl radicals by Fenton s... 

MW 98.91 CAS [75-44-5] formed in air in trace amounts by photodecomposition of chlorinated solvent vapors used in the synthesis of dyes and pesticides, and as a war gas colorless suffocating odor at low ppm concentration sweet hay-like odor at low ppb concentration liquefies at 8°C solidifies at -118°C density 1.43 g/mL at 0°C slightly soluble in water (reacting slowly), soluble in hexane, benzene, and glacial acetic acid highly poisonous. 

Crosby, D.G., Wong, A.S., Plimmer, J.R., Woolson, E.A. (1971) Photodecomposition of chlorinated dibenzo-p-dioxins. Science 173,... 

Crosby, D.G.,Moilanen,K.W. (1973) Photodecomposition of chlorinated biphenyls and dibenzofurans. Bull. Environ. Contam. Toxicol. 6, 372. 

Surely, many such common reactions could be utilized for the intentional destruction of unwanted herbicides and their residues (41). Metham might be caused to react simply with aqueous ammonia to form harmless methylthiourea many herbicides including prometryne and metribuzin (Sencor) might be degraded by dilute hypochlorite ("chlorinated lime") of the type used to purify swimming pools, and the photodecomposition of others (such as 2,4,5-T) might be accelerated by cheap nontoxic photosensitizers such as acetone (Table III) (42). The variations of environmental chemistry applications to control and direct herbicide persistence and effectiveness now appear endless. 

H2BPurhep), as in chlorins (81,93,94). The success of these strategies can be best evaluated in terms of the photodecomposition quantum yields of the sensitizers. 

Other drugs studied by Moore et al. include chlorine containing photosensitizers (178), the effect of surfactants on photosensitizers (179), photosensitization by malarial drugs (180), nalidic and oxolinic acids (181), 6-mercaptopurine (182), azathioprine and nitroimidazole (183), 7-methylbenz[c]acridine and related products (184), naproxen, ben-oxaprofen and indomethacin (185), mefloquine (186), sulfamethoxazole and trimethoprim (187), benzydamine (188), photodecomposition of hydrochlorthiazide (189), tetracycline (190), frusemide (191), 6-mercaptopurine (192), 7-methylbenz[c]acridine (193), metronidazole, misonidazole and azathioprine (194), misonidazole and metronidazole (195), benzydamine (196), components in drug formulations (197) and sulfamethoxazole (198,199). 

One possible explanation for this trend Is that bound PCB s derived from an atmospheric source and were associated with soot particles. Several physicochemical properties of PCB s could favor the generation of atmospheric assemblages enriched In less chlorinated Isomers laboratory studies of PCB s demonstrate that there Is a trend toward higher vapor pressure with decreasing chlorine content (37) and that photodecomposition selectively destroys higher... 

Photolysis has had limited application for treatment of hazardous waste or detoxification of chemically contaminated materials. The susceptibility of chlorinated aromatics, including herbicides such as 2,4-D and 2,4,5-T, to UV-induced decomposition is well established (7,8). Photodecomposition of such compounds leads to successive dechlorination followed by condensation reactions to form phenolic polymers (7,8). Other research has demonstrated that CDD and CDF decompose in the presence of UV light (8,9,10) Development of a photochemical process for destroying 2,3,7,8-TCDD in a waste tar indicated similar dechlorination and condensation reactions and products (8). The high-molecular weight end products, which are similar in structure to humic acids, would be expected to have low toxicity and mobility. Therefore, essentially complete... 

The carbonyl halides thus formed also are subject to photodecomposition whereby further chlorine (or fluorine) atoms are released. Their interaction with ozone results in the catalytic cycle... 

In this reaction sequence ozone is reconstituted so that there is no net loss. Yet another link between the CIO and NO families is the formation of chlorine nitrate and its photodecomposition ... 

Particular interest has been shown in the reactions of photochemically generated arylcarbenes. A study of the photodecomposition of phenyldiazomethane in 2-chloropropane has revealed that carbon-chlorine bond insertion of singlet phenylcarbene predominates at low temperature in solution, whereas carbon-hydrogen bond insertion is preferred in a rigid matrix. The principal products of irradiation of diazoalkane (63) are phenylacetylene (64) and the cyclobutene (65), even in the presence of alkenes. At lower temperatures, however, carbene addition predominates as shown, for example, with isobutene as shown in Scheme 7. 

E. A. Woolson. 1971. Photodecomposition of chlorinated dibenzo-p-dioxins. Science 195 1337-38. 

Phosgene is used in the synthesis of dyes, pharmaceuticals, isocyanates, and pesticides and as a war gas. Exposure risk to this gas may arise when many common solvents, such as carbon tetrachloride, chloroform, or methylene chloride, are intensely heated. Photodecomposition of these solvents in air or oxygen can also generate phosgene in small amounts. It is also formed by the reaction of carbon tetrachloride with oleum, or of carbon monoxide with chlorine or nitrosyl chloride. 

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