Kinetics and Mechanism of the Oxidation of Aquated Sulfur Dioxide by Hydrogen Peroxide at Low pH

Article abstract of DOI:10.1021/j150644a024

A stopped-flow kinetic study of the oxidation of sulfur dioxide by hydrogen peroxide was performed over the pH range 0.0-4.5.A rate expression of the following form was verified experimentally: d/dt = k₁K_a1(k₂+> + k₃)/<(k_-1 + k₂+> + k₃)(K_a1 + +>)>.The following kinetic parameters at 15 deg C were determined: k₁ = (2.6 +/- 0.5)*10⁶ M^-1 s^-1, k₂/k_-1 = 16 +/- 4 M^-1, k₂/k₃ = (5 +/- 1)*10² (HA = acetic acid), ΔH(excit.)₁ = 37 +/- 2 kJ mol^-1, and ΔS(excit.)₁ = 4 +/- 4 J K^-1 mol^-1.The reaction proceeds via a nucleophilic displacement of HSO3^-1 by H2O2 to which undergoes sulfurous acid intermediate which undergoes acid-catalyzed rearrangement to form product: SO2*H2O <-> HSO3^- + H⁺(K_a1), H2O2 + HSO3^- <-> HOOSO2^- (k₁, k_-1), HOOSO2^- + H⁺ -> H⁺ + HSO4^- (k₂), HOOSO2^- + HA -> HA + HSO4^- (k₃).Application of the above rate expression to reactions occuring in hydrometeors is discussed.