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] and much higher [BrO] than in traditional studies of this reaction. In fact, pH oscillations were obtained in the presence of only BrO, malonic acid (MA), and Mn. The amplitude, frequency, and duration of oscillations tend to depend primarily on the ratio of [BrO] to [MA]. 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 Mn. 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.