Discovery of Novel Bromate−Sulfite pH Oscillators with Mn2+ or MnO4- as a Negative-Feedback Species

A novel pH oscillator has been constructed by combining the pH clock reaction system BrO 3 - −SO 3 2- −H + with Mn 2+ as a proton-consuming species. The system exhibits large-amplitude pH oscillations typically between pH = 2.8 and pH = 7.3 at 45 °C in a continuous-flow stirred tank reactor. The oscillatory waveform is similar to that of a pulse wave, and the duration of both high-pH and low-pH stages can be changed in a wide range by controlling the input concentrations of BrO 3 - and Mn 2+ . The state diagram spanned by the input concentrations of BrO 3 - and Mn 2+ takes the form of a cross-shaped diagram. It has been found that MnO 4 -, in place of Mn 2+, is also effective in consuming H + to give large-amplitude pH oscillations. A possible reaction mechanism for the removal of H + has been discussed in which MnO(OH) + is reduced by HSO 3 - to give HS 2 O 6 - . This properly accounts for the stoichiometry for both the Mn 2+ and MnO 4 - systems. The proposed reaction scheme is unique among pH oscillators reported so far in that the sulfite ion plays a key role in both the nonlinear production and consumption of protons.