Rate constants for the reactions of chloride monoxide radical (ClO•) and organic molecules of environmental interest

Abstract

ClO• plays a key role in the UV/chlorine process besides Cl•, Cl2• − , and •OH. In many experiments, ClO• proved to be the main reactant that destroyed the organic pollutants in advanced oxidation process. About 200 rate constants of ClO• reactions were collected from the literature, grouped together according to the chemical structure, and the molecular structure dependencies were evaluated. In most experiments, ClO• was produced by the photolytic reaction of HClO/ClO−. For a few compounds, the rate constants were determined by the absolute method, pulse radiolysis. Most values were obtained in steady-state experiments by competitive technique or by complex kinetic calculations after measuring the pollutant degradation in the UV/chlorine process. About 30% of the listed rate constant values were derived in quantum chemical or in structure-reactivity (QSAR) calculations. The values show at least six orders of magnitude variations with the molecular structure. Molecules having electron-rich parts, e.g., phenol/phenolate, amine, or sulfite group have high rate constants in the range of 108–109 mol−1 dm3 s−1. ClO• is inactive in reactions with saturated molecules, alcohols, or simple aromatic molecules. HIGHLIGHTS ClO• has high rate constants with molecules having electron-rich activated parts.; ClO• has low reactivity with saturated molecules, alcohols, and simple aromatics.; For most compounds, only one published value is available.; Values obtained in different laboratories show a large scatter.;

Keywords

• clo• radical reactivity
• competitive technique
• pollutant degradation
• structure dependence
• uv/chlorine process
• wastewater