The ferroin-catalyzed Belousov-Zhabotinskii system with a “clock” behaviour

The Autocatalytic Reduction of Ferriin by Malonic Acid with Regard to the Ferroin-Catalyzed Belousov-Zhabotinsky Reaction

The reduction of ferriin ([Fe(phen)3]3+, phen = 1,10-phenanthroline) by malonic acid (MA) differs from the reduction of Ce(IV) or Mn(III) ions by MA in its autocatalytic character and in a pregnant influence of oxygen, which behaves obviously as a catalyst. The time dependence of the ferroin-ferriin redox potential at the last stage of this reaction has a sigmoidal shape, which indicates autocatalysis. Under anaerobic conditions, the inflection time is of the order of several tens of minutes, since autocatalysis cannot proceed unless a sufficient amount of oxygen is produced via oxidation of water (OH- ions) with Fe(IV) formed by the ferriin dismutation. Under aerobic conditions, the inflection time decreases to a value of a few seconds. The probable reaction mechanism is discussed in detail.