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 reacti on system BrO3--SO32--H+ with Mn2+ as a proton-consuming species. The syste m exhibits large-amplitude pH oscillations typically between pH = 2.8 and p H = 7.3 at 45 degrees C in a continuous-flow stirred tank reactor. The osci llatory waveform is similar to that of a pulse wave, and the duration of bo th high-pH and low-pH stages can be changed in a wide range by controlling the input concentrations of BrO3- and Mn2+. The state diagram spanned by th e input concentrations of BrO3- and Mn2+ takes the form of a cross-shaped d iagram. It has been found that MnO4-, in place of Mn2+, is also effective i n 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 HSO3- to give HS2O6-. This properly accounts for the stoichiomet ry for both the Mn2+ and MnO4- systems. The proposed reaction scheme is uni que among pH oscillators reported so far in that the sulfite ion plays a ke y role in both the nonlinear production and consumption of protons.