Rate Constants and Mechanisms for Reactions of Bromine Radicals with Trace Organic Contaminants

Bromine radicals can pose great impacts on the photochemical transformation of trace organic contaminants in natural and engineered waters. However, the reaction kinetics and mechanisms involved are barely known. In this work, second-order reaction rate constants with Br-center dot and Br-2(center dot-) were determined for 70 common trace organic contaminants and for 17 model compounds using laser flash photolysis and steady-state competition kinetics. The k(Br)center dot values ranged from <108 to (2.86 +/- 0.31) x 10(10) M-1 s(-1) and the k(Br2 center dot)- values from <10(5) to (1.18 +/- 0.09) x 10(9) M-1 s(-1) at pH 7.0. Six quantitative structure-activity relationships were developed, which allow predicting additional unknown k(Br)center dot and k(Br2)center dot- values. Single-electron transfer was shown to be a favored pathway for the reactions of Br center dot and Br-2 center dot- with trace organic contaminants, and this was supported by transient spectroscopy and quantum chemical calculations. This study is essential in advancing the scientific understanding of halogen radical-involved chemistry in contaminant transformation.

Automated summary

This study determined the reaction kinetics parameters of bromine radicals in the photochemical transformation of trace organic contaminants in natural and engineered waters. It was found that bromine radicals mainly react with contaminants through a single-electron transfer pathway.