Vapor-phase photodecomposition

Other environmental properties of interest are those that govern movement of chemicals, for these properties can influence not only the possibility of human exposure but also the lifetime and fate of the chemical. Clearly, if a nitrosamine is formed in, or introduced into, the soil and stays there, it presents little threat to man, and its lifetime will depend on the chemical or microbiological properties of the soil. If it should move to the surface and volatilize into the atmosphere, on the other hand, there will exist the possibility of human exposure via inhalation and also the possibility of vapor-phase photodecomposition. If a nitrosamine were to leach from soil into water, it could perhaps be consumed in drinking water alternatively, exposure of the aqueous solution to sunlight could provide another opportunity for photodecomposition. 

When an aqueous solution containing 1,4-dichlorobenzene (190 pM) and a nonionic surfactant micelle (Brij 58, a polyoxyethylene cetyl ether) was illuminated by a photoreactor equipped with 253.7-nm monochromatic UV lamps, photoisomerization took place, yielding 1,2- and 1,3-dichlorobenzene as the principal products. The half-life for this reaction, based on the first-order photodecomposition rate of 1.34 x 10 /sec, is 8.6 min (Chu and Jafvert, 1994). A room temperature rate constant of 3.2 x lO cmVmolecule-sec was reported for the vapor-phase reaction of 1,4-dichlorobenzene with OH radicals (Atkinson, 1985). 

Crosby, D.G. and Leitis, E. Photodecomposition of chlorobenzoic acids, /. Agric. Food Chem., 17(5) 1033-1035, 1969. Crosby, D.G. and Moilanen, K.W. Vapor-phase photodecomposition of aldrin and dieldrin. Arch. Environ. Contam. Toxicol, 2(l) 62-74, 1974. 

A number of reports of photochemical decomposition of heteroaromatic compounds have appeared in the literature during the past 50 or 60 years. A few of these undoubtedly involve photooxidative processes, whereas others have been examined in the vapor phase, often at elevated temperatures. Recent work includes the study of the photodecomposition of thiophene128 andpyrazine.129 Furans undergo... 

Crosby, D.G. Moilanen, K.W. Vapor-phase photodecomposition of aldrin and dieldrin. Arch. Environ. Contamin. Toxicol., 1974, 2, 62. 

Moilanen, K.W., D.G Crosby, J.R. Humphrey, and J.W. Giles (1978), Vapor-phase photodecomposition of chloropicrin (Irichloronitromethane), Tetrahedron, 34, 3345-3349. Molina, L.T., and M.J. MoUna (1981), UV absorption cross-sections of HO2NO2 vapor, J. Photochemistry, 15, 97-108. 

Evidence of Photodissociation of Water Vapor on Reduced SrTiCh (III) Surfaces in a High Vacuum Environment. First report of photodecomposition of water adsorbed from the gas phase in high vacuum conditions on metal-free, reduced single crystals. 396... 

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