Production of Hydroxyl Radical via the Activation of Hydrogen Peroxide by Hydroxylamine

The production of the hydroxyl radical (HO center dot) is important in environmental chemistry. This study reports a new source of HO center dot generated solely from hydrogen peroxide (H2O2) activated by hydroxylamine (HA). Electron paramagnetic resonance analysis and the oxidation of a HO center dot probe, benzoic acid, were used to confirm the production of HO center dot. The production of HO center dot increased with increasing concentrations of either HA or H2O2 as well as decreasing pH. The second-order rate constant for the reaction was (2.2 +/- 0.2) x 10(-4) M-1 s(-1). HO center dot was probably produced in two steps: the activation of H2O2 by protonated HA and then reaction between the H2O2 and the intermediate protonated aminoxyl radical generated in the first step. Such a two-step oxidation can possibly be ascribed to the ionizable hydroxyl moiety in the molecular structure of HA, as is suggested by comparing the reactivity of a series of HA derivatives in HO center dot production. The results shed light on a previously unknown source of HO center dot formation, which broadens the understanding of its role in environmental processes.