Homogeneous hydrolysis rate constants for selected chlorinated methanes, ethanes, ethenes, and propanes

Abstract

Hydrolysis rate constants of 18 chlorinated methanes, ethanes, ethenes, and propanes were measured in dilute aqueous solutions within the temperature range of 0 to 180 C and at pH values of 3 to 14. Arrhenius parameters were determined for both neutral and alkaline hydrolysis reactions. Reactivity of these compounds in basic solutions increases in accord with the expected acidity of the most reactive hydrogen atom in the molecule. Neutral hydrolysis appears to depend on both the C-Cl bond strength and the degree of steric hindrance at the reaction site. Only a neutral hydrolysis process occurs for CCl{sub 4}, 1,1,1-trichloroethane, and 2,2-dichloro-propane. The chlorinated ethenes and hexachloroethane react only with hydroxide under severe conditions and exhibit no neutral hydrolysis. Some of these compounds eliminate HCl, whereas others substitute OH for Cl to form alcohols that may react further to give aldehydes or carboxylic acids as products. Environmental hydrolysis half-lives (25 C, pH 7) range from 36 h for 2,2-dichloropropane to 1850 years for CHCl{sub 3} and to more than 1,000,000 years for C{sub 2}Cl{sub 6} and the ethenes.