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 (k_obs = k_o + k_OH⁻ × [OH⁻]; ClCH₂C(O)O⁻: A_o 6.4 × 10¹⁵ s⁻¹, E_o 148 kJ mol⁻¹, A_OH⁻ 1.6 × 10⁹ dm³ mol⁻¹ s⁻¹, E_OH⁻ 86 kJ mol⁻¹. Cl₂CHC(O)O⁻: A_o 3.2 × 10¹⁶ s⁻¹, E_o 156 kJ mol⁻¹, A_OH⁻ 3.2 × 10¹⁰ dm³ mol⁻¹ s⁻¹, E_OH⁻ 104 kJ mol⁻¹). Trichloroacetate anion decomposes by another mechanism, undergoing decarboxylation which is base-uncatalyzed: A_o 2.1 × 10¹⁷ s⁻¹, E_o 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.