Some General Features in the Autocatalytic Reaction between Sulfite Ion and Different Oxidants


  • Contract grant sponsor: Hungarian Scientific Research Fund.

  • Contract grant numbers: OTKA 77986, 100891.

Correspondence to: István Szalai; e-mail:


The autocatalytic oxidation of a weak acid is a common building block of the pH oscillators. These reactions can be described by a simple general scheme that includes a protonation equilibrium and the oxidation of the protonated form of the weak acid. Here we show that independently from the chemical nature of the oxidizing agent, these reactions bear some general features, namely (1) the change in pH (ΔpH) observed during the reaction is determined by the acidity constant (KHA) and by the initial concentration of the unprotonated form of the weak acid (A): math formula, (2) the inflection time of the autocatalytic reaction (ti) depends reciprocally on KHA and on the initial hydrogen ion concentration, and (3) in the presence of a competitive reversible proton-binding component (D), that is not involved in the oxidation process, ΔpH follows a titration-like curve as the concentration of D is increased, ti is only slightly affected but the maximum rate of the autocatalytic process is significantly reduced. The slowing of the overall reaction is proportional to the acidity constant of the proton-binding component.