Kinetics and Mechanisms of Aqueous Ozone Reactions with Bromide, Sulfite, Hydrogen Sulfite, Iodide, and Nitrite Ions

Reactions of ozone with Br-, SO3 2-, HSO3 -, I-, and NO2 -, studied by stopped-flow and pulsed-accelerated-flow techniques, are first order in the concentration of O3(aq) and first order in the concentration of each anion. The rate constants increase by a factor of 5 × 106 as the nucleophilicities of the anions increase from Br- to SO3 2-. Ozone adducts with the nucleophiles are proposed as steady-state intermediates prior to oxygen atom transfer with release of O2. Ab initio calculations show possible structures for the intermediates. The reaction between Br- and O3 is accelerated by H+ but exhibits a kinetic saturation effect as the acidity increases. The kinetics indicate formation of BrOOO- as a steady-state intermediate with an acid-assisted step to give BrOH and O2. Temperature dependencies of the reactions of Br- and HSO3 - with O3 in acidic solutions are determined from 1 to 25 °C. These kinetics are important in studies of annual ozone depletion in the Arctic troposphere at polar sunrise.