Carbon tetrachloride degradation results

The highest yield of degradation products (HDBP, H2MBP, phosphoric acid, carbonyl compounds) occurred in the TBP-CC14-HN03 system (87). As a result, it has been suggested that the considerable amounts of hydrochloric acid produced could accelerate the process of degradation. On the other hand, the use of carbon tetrachloride as diluent resulted in a very low yield of nitro compounds. An important sensitization effect was also reported by Nash with tetrachloroethylene G(-TBP) = 3.8 0.6 and 9.2 3 for pure molecule and TCE solution (41). 

The first term, representing acid-"catalyzed" hydrolysis, is important in reactions of carboxylic acid esters but is relatively unimportant in loss of phosphate triesters and is totally absent for the halogenated alkanes and alkenes. Alkaline hydrolysis, the mechanism indicated by the third term in Equation (2), dominates degradation of pentachloroethane and 1,1,2,2-tetrachloroethane, even at pH 7. Carbon tetrachloride, TCA, 2,2-dichloropropane, and other "gem" haloalkanes hydrolyze only by the neutral mechanism (Fells and Molewyn-Hughes, 1958 Molewyn-Hughes, 1953). Monohaloalkanes show alkaline hydrolysis only in basic solutions as concentrated as 0.01-1.0 molar OH- (Mabey and Mill, 1978). In fact, the terms in Equation(2) can be even more complex both elimination and substitution pathways can operate, leading to different products, and a true unimolecular process can result from initial bond breaking in the reactant molecule. 

Table 2.8 compares hydrolysis half-lives with half-lives for reaction with sulfur-based nucleophiles for several halogenated aliphatics. These data show that the environmental half-lives for substrates such as 1-bromohexane and 1,2-dibromoethane can be substantially reduced in the presence of HS and polysulfides. Enhanced degradation of 2-bromopropane and 1,1,1-trichloroethane, as well as chloroform and carbon tetrachloride (results not shown) was not observed, suggesting that steric hindrance significantly impedes reaction with the sulfur based nucleophiles (Haag and Mill, 1988a). 

During their investigation on the dechlorination of carbon tetrachloride (CT) and chloroform (CF), Lien and Zhang (38) found that in chlorinated organic water solution or mixtures, Fe p) particles were predominantly suspended in the liquid phase while Fe° (microscale) usually settled at the bottom of the bottle. Therefore, initial diffusion and subsequent transport of the chlorinated organics to the suspended Fe p) may have resulted in the faster degradation achievable with Fe p) compared to Fe°. 

Benzophenone was used as photosensitizer in a study of the photo-decomposition of benzene solutions of polystyrene and poly(a-methyl styrene). Laser photolysis (A 265 nm) of poIy(a-methyl styrene) in chlorofonn and carbon tetrachloride proceeded by attack of solvent radicals in the polymer molecules resulting in main chain cleavage. " A series of papers have been devoted to the study of the photo-induced decomposition of poly(a-methyl styrene) in benzene solutions, using a,a -bisisobutyronitrile, benzophenone, and triphenyl-methyl cations as sensitizers. Spin-trapping techniques were used to detect transient radicals formed during benzophenone-sensitized degradation of poly-(a-methyl styrene). The rate constant for intramolecular reaction of the macroradical was estimated. 

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