Oxidation of chlorinated ethenes by potassium permanganate: a kinetics study

Abstract

The kinetics of oxidation of perchloroethylene (PCE), trichloroethylene (TCE), three isomers of dichloroethylene (DCE) and vinyl chloride (VC) by potassium permanganate (KMnO 4) were studied in phosphate-buffered solutions of pH 7 and ionic strength ∼0.05 M and under isothermal, completely mixed and zero headspace conditions. Experimental results have shown that the reaction appears to be second order overall and first order individually with respect to both KMnO 4 and all chlorinated ethenes (CEs), except VC. The degradation of VC by KMnO 4 is a two-consecutive-step process. The second step, being the rate-limiting step, is of first order in VC and has an activation energy ( E a) of 7.9±1 kcal mol −1. The second order rate constants at 20°C are 0.035±0.004 M −1 s −1 (PCE), 0.80±0.12 M −1 s −1 (TCE), 1.52±0.05 M −1 s −1 ( cis-DCE), 2.1±0.2 M −1 s −1 (1,1-DCE) and 48.6±0.9 M −1 s −1 ( trans-DCE). The E a and entropy (Δ S ∗) of the reaction between KMnO 4 and CEs (except VC) are in the range of 5.8–9.3 kcal mol −1 and −33 to −36 kcal mol −1 K −1, respectively. Moreover, KMnO 4 is able to completely dechlorinate CEs, and the increase in acidity of the solution due to CE oxidation by KMnO 4 is directly proportional to the number of chlorine atoms in CEs.