Free radical chemistry of disinfection-byproducts. 1. Kinetics of hydrated electron and hydroxyl radical reactions with halonitromethanes in water

Halonitromethanes are disinfection-byproducts formed during ozonation and chlorine/chloramine treatment of waters that contain bromide ion and natural organic matter. In this study, the chemical kinetics of the free-radical-induced degradations of a series of halonitromethanes were determined. Absolute rate constants for hydroxyl radical, ̇OH, and hydrated electron, e _aq ^-, reaction with both chlorinated and brominated halonitromethanes were measured using the techniques of electron pulse radiolysis and transient absorption spectroscopy. The bimolecular rate constants obtained, k (M ^-1 s ^-11), for e _aq ^-/̇OH, respectively, were the following: chloronitromethane (3.01 ± 0.40) × 10 ¹⁰/(1.94 ± 0.32) × 10 ⁸; dichloronitromethane (3.21 ± 0.17) × 10 ¹⁰/(5.12 ± 0.77) × 10 ⁸; bromonitromethane (3.13 ± 0.06) × 10 ¹⁰/(8.36 ± 0.57) × 10 ⁷; dibromonitromethane (3.07 ± 0.40) × 10 ¹⁰/(4.75 ± 0.98) × 10 ⁸; tribromonitromethane (2.29 ± 0.39) × 10 ¹⁰/(3.25 ± 0.67) × 10 ⁸; bromochloronitromethane (2.93 ± 0.47) × 10 ¹⁰/(4.2 ± 1.1) × 10 ⁸; bromodichloronitromethane (2.68 ± 0.13) × 10 ¹⁰/(1.02 ± 0.15) × 10 ⁸; and dibromochloronitromethane (2.95 ± 0.43) × 10 ¹⁰ / (1.80 ± 0.31) × 10 ⁸ at room temperature and pH ∼7. Comparison data were also obtained for hydroxyl radical reaction with bromoform (1.50 ± 0.05) × 10 ⁸, bromodichloromethane (7.11 ± 0.26) × 10 ⁷, and chlorodibromomethane (8.31 ± 0.25) × 10 ⁷ M ^-1 s ^-1, respectively. These rate constants are compared to recently obtained data for trichloronitromethane and bromonitromethane, as well as to other established literature data for analogous compounds.