Cross-Reaction Mechanism between HNO2 and C6H5Br in Aqueous Solution under Irradiation at 355 nm

The reaction mechanism between HNO2 and C6H5Br in aqueous solution in the presence or absence of O2 was studied using laser flash photolysis transient absorption spectrum technique under irradiation at 355 nm. The experimental results suggested the generation of ·OH radical through the photolysis of HNO2. The addition of ·OH radical to bromobenzene to form an OH-adduct, C6H5Br···OH, involved a second-order rate constant of (8.1±0.7)× 109 L·mol−1·s−1. C6H5Br···OH could be oxidized by O2 or HNO2. The second-order rate constant (3.0±0.5)× 107 L·mol−1·s−1 for the reaction of C6H5Br···OH with HNO2 was much lower than (4.0±0.6)× 108 L·mol−1·s−1 for the reaction of C6H5Br···OH with O2. The decay constant of C6H5Br···OHO2 produced by the reaction of C6H5Br···OH with O2 was (2.4± 0.1)× 104 s−1. Gas chromatographic and mass spectrometric (GC-MS) analysis suggested the formation of multiple compounds containing nitryl or quinone formed by the reaction of C6H5Br···OH with HNO2 or O2.