Hydrolytic removal of the chlorinated products from the oxidative free-radical-induced degradation of chloroethylenes: acid chlorides and chlorinated acetic acids

Abstract

Progressive hydrolytic decomposition of acyl chlorides, among them the chlorinated acetyl chlorides, which are produced in the gas-phase oxidation of chlorinated ethylenes, permits the complete mineralization of organically bound chlorine to chloride anion. Hydrolysis rate constants (100% water) have been determined for the following acyl chlorides: acetyl (350 s−1), chloroacetyl (5.5 s−1), dichloroacetyl (300 s−1), trichloroacetyl (>350 s−1), and oxalyl dichloride (>350 s−1). The chlorinated acetyl chlorides thereby give rise to the chloroacetates whose decomposition has also been studied and the kinetic parameters determined. Mono- and dichloroacetate anion undergo hydrolytic dechlorination (kobs = ko + kOH− × [OH−]; ClCH2C(O)O−: Ao 6.4 × 1015 s−1, Eo 148 kJ mol−1, AOH− 1.6 × 109 dm3 mol−1 s−1, EOH− 86 kJ mol−1. Cl2CHC(O)O−: Ao 3.2 × 1016 s−1, Eo 156 kJ mol−1, AOH− 3.2 × 1010 dm3 mol−1 s−1, EOH− 104 kJ mol−1). Trichloroacetate anion decomposes by another mechanism, undergoing decarboxylation which is base-uncatalyzed: Ao 2.1 × 1017 s−1, Eo 146 kJ mol−1. Procedures on a pilot-plant scale are pointed out that allow the elimination of these compounds upon oxidation of the strip-gas produced when contaminated water is freed from chlorinated ethylenes by air-stripping.