Reactivity of OH radicals with chlorobenzoic acids—A pulse radiolysis and steady-state radiolysis study

Abstract

The reactions of OH radicals with 2-, 3-, 4-chlorobenzoic acids (ClBzA) and chlorobenzene (ClBz), k( OH+substrates)=(4.5−6.2)×10 9 dm 3 mol −1 s −1, have been studied by pulse radiolysis in N 2O saturated solutions. The absorption maxima of the OH-adducts were in the range of 320−340 nm. Their decay was according to a second-order reaction, 2 k=(1−9)×10 8 dm 3 mol −1 s −1. In the presence of N 2O/O 2 the formation of peroxyl radicals was detectable for 2-, 4-ClBzA and ClBz, k(OH-adduct+O 2)=(2−4)×10 7 dm 3 mol −1 s −1, while this reaction for 3-ClBzA was too slow to be registered. In the presence of N 2O the degradation rates induced by gamma radiation were very similar for all chlorobenzoic acids, yet the chloride formation was distinctly higher for 3-ClBzA. In the presence of oxygen the initial degradation of 2-and 4-ClBzA equaled the OH-radical concentration, whereas in case of 3-ClBzA only ∼60% of OH led to degradation. The order for the efficiency of dehalogenation was 4->2->3-ClBzA. Several primary radiolytic products could be detected by HPLC. To evaluate the toxicity of final products a bacterial bioluminescence test was carried out.