The Belousov-Zhabotinsky oscillating reaction (BZR) is the model oscillating reaction in the field of non-linear chemical dynamics. The BZR consists of the metal-catalyzed bromate oxidation of a dicarboxylic acid in dilute sulfuric acid. We study the bromate oxidation of malonic acid (MA) catalyzed by the Fe(II)/Fe(III) couple. Oscillations are visible because of the colors associated with the different oxidation states of the metal species: Red Fe(II) and blue Fe(III). We have been studying the BZR with experimental measurements, mathematical modeling, and mechanistic analysis. In the laboratory, we found experimental conditions that allowed for the reliable reproduction of BZ reactions with variations of selected parameters (sulfuric acid concentration and pH) and the video-recording of the reactions. The analysis of the videos involves several layers of mathematical modeling. Color analysis of the video frames as a function of time gives time traces associated with characteristic colors (Fig. 1). Extrema analysis of the time traces allowed for the extraction of timing information and, specifically, the period times PT(ti), oxidation times OT(ti), and reduction times RT(ti) over time. The results of the kinetic analysis allow for a refinement the mechanistic understanding of the oscillating reactions. Kinetic simulations implicate the oxidation of bromomalonic acid (BMA), that is, the step returning bromide ions, as the cause of the acidity dependence of the oscillation parameters. Ligand dissociation of the catalyst and protonation of free phenanthroline and of the organic substrates MA and BMA determine the rate of this step. We will highlight new results on the acidity dependence of key parameters describing the oscillating reactions catalyzed by the Fe(II)/Fe(III) redox couple.

Confronting the complexity of nonlinear systems. Acid-dependency of the Fe-catalyzed Belousov-Zhabotinsky oscillating chemical reaction

255th National Meeting (2018)

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