Aliphatic compounds, atmosphere

See Airpollution Atmospheric models Fluorine compounds, organic-fluorinated aliphatic compounds Ozone. 

Nitropyrene was the sole product formed from the gas-phase reaction of pyrene with OH radicals in a NOx atmosphere (Arey et al, 1986). Pyrene adsorbed on glass fiber filters reacted rapidly with N2O5 to form 1-nitropyrene. When pyrene was exposed to nitrogen dioxide, no reaction occurred. However, in the presence of nitric acid, nitrated compounds were produced (Yokley et al, 1985). Ozonation of water containing pyrene (10-200 pg/L) yielded short-chain aliphatic compounds as the major products (Corless et al, 1990). A monochlorinated pyrene was the major product formed during the chlorination of pyrene in aqueous solutions. At pH 4, the reported half-lives at chlorine concentrations of 0.6 and 10 mg/L were 8.8 and <0.2 h, respectively (Mori et al, 1991). 

Significantly slower rates are found only for compounds that do not exhibit any aromatic ring or carbon-carbon double bond, and for aliphatic compounds with no easily abstractable H-atoms. Such H-atoms include those that are bound to carbon atoms carrying one or several electronegative heteroatoms or groups. (Note that the stabilization of a carbon radical (R ) is similar to that of a carbocation.) We will come back to such structure-reactivity considerations in Section 16.3, when discussing reaction of HO" with organic pollutants in the gas phase (i.e., in the atmosphere). 

It has been hypothesized on the basis of the formation of trichlo-roacetate from aliphatic compounds, especially acetate, by the action of chloroperoxidase in the presence of hydrogen peroxide and chloride that this might be a naturally occurring metabolite (Haiber et al. 1996). Plausible mechanisms for the formation of trichloroacetic acid by atmospheric reactions involving trichloro-ethane and tetrachloroethene are discussed in Section 4.1.2. 

In addition, the alkoxy radical C13C.CH20 produces highly reactive phosgene (COCl2) (Platz et al. 1995 Nelson et al. 1990) that has been identified in atmospheric samples and was attributed to the transformation of gem-dichloro aliphatic compounds (Grosjean 1991). 

Oxidative transformations, as noted above, are more likely to be induced by enzyme-catalyzed processes in biota or photoinduced reactions in the atmosphere or in water. Consequently, this analysis will focus on reductions. The carbon of halogenated aliphatic compounds shows a high positive oxidation state (Table 7.1) and thus these compounds would be candidates for reduction. Since these compounds have been used extensively and may be released into the environment, it is useful to assess the significance of these transformation processes. 

An antipolymerization agent such as hydroquinone may be added to the reaction mixture to inhibit the polymerization of the maleate or fumarate compound under the reaction conditions. This reaction is preferably carried out at a temperature within the range of 20°C to 150°C. This reaction is preferably carried out at atmospheric pressure. Reaction time of 16 to 24 hours have bean specified for this reaction by J.T. Cassaday. The reaction is preferably carried out in a solvent such as the low molecular weight aliphatic monohydric alcohols, ketones, aliphatic esters, aromatic hydrocarbons or trialkyl phosphates. 

Sawicki, E., S. P. McPherson, T. W. Stanley, J. Meeker, and W. C. Elbert. Quantitative composition of the urban atmosphere in terms of polynuclear aza heterocyclic compounds and aliphatic and polynuclear aromatic hydrocarbons. Int. J. Air Water Pollut. 9 515-524, 1%5. 

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