Acid formation in the radical-mediated degradation of chlorinated ethanes in aqueous environment. A radiation chemical study

Abstract

High yields of HCl and organic acids RCOOH are found to result from a one-electron- and ˙OH-radical-induced degradation of polychlorinated ethanes in oxygen-containing aqueous solutions. The following organic acids (depending on the initiating radical e_aq^– or ˙OH) have been identified and quantitatively been measured: CH₃COOH from 1,1,1-trichloroethane and 1,1-dichloroethane; CH₂ClCOOH from 1,2-dichloroethane and 1,1,2-trichloroethane; CHCl₂COOH from 1,1,2-trichloroethane; HCOOH from 1,2-dichloroethane and 1,1,2-trichloroethane; and CO₂ from all substrates. The mechanism of the organic acid formation proceeds via peroxyl radicals as key intermediates. The nature of the latter must be either RCCl₂OO˙ or RCHClOO˙, i.e. the carbon atom carrying the peroxyl group must also carry at least one chlorine atom. The present radiation chemical findings corroborate other observations made in the one-electron- and free-radical-induced degradation of various individual halogenated alkanes and may therefore be generalized. The studies help to provide a chemical understanding of the biological and environmental action of halogenated compounds in general.