Trichloroacetic acid dehalogenation by reductive radicals

Advanced oxidation processes, using either UVC/H2O2 or UVC/K2S2O8, both in the presence of H2CO2 or CH3OH are very efficient in mineralizing aqueous solutions of trichloroacetic acid (TCAA) leaving no toxic residues. The main reaction initiating TCAA depletion is its reduction by the radicals View the MathML sourceCO2- or radical dotCH2OH to yield View the MathML sourceCCl2CO2- radicals and Cl− anions. Further thermal reactions of View the MathML sourceCCl2CO2- lead to the formation of CO2 and HCl. Molecular oxygen competes with TCAA for View the MathML sourceCO2- and radical dotCH2OH radicals. However, in experiments under continuous irradiation of initially air-saturated solutions in closed reactors, the dissolved molecular oxygen concentration was depleted to low enough levels to favor the reaction of the reducing radicals with TCAA. A general reaction mechanism is proposed and discussed. The reaction between superoxide radical anions and TCAA was found to be of low efficiency.