Batch pH Oscillations in the Belousov-Zhabotinsky Reaction

No single-phase system has been previously reported to give significant pH oscillations in a closed (batch) reactor. We report here sustained pH oscillations in batch for the Belousov-Zhabotinsky reaction using much lower [H⁺]₀ and much higher [BrO₃^-]₀ than in traditional studies of this reaction. In fact, pH oscillations were obtained in the presence of only BrO₃^-, malonic acid (MA), and Mn²⁺. The amplitude, frequency, and duration of oscillations tend to depend primarily on the ratio of [BrO₃^-]₀ to [MA]₀. A critical part of the proposed mechanism involves the reversible formation of a manganese(III) complex with bromomalonic acid, followed by two-electron oxidation to tartraric acid and Mn²⁺. Estimates of the corresponding rate constant values for these reactions have been obtained by simulation. It is suggested that the presence of a supercatalytic reaction in H⁺ may be a sufficient, if not necessary, requirement for the occurrence of pH oscillations in a batch system.