Effect of vanadium (IV, V) ions on the Belousov ? Zhabotinskii oscillating reaction

Abstract

Mechanistic features of the periodic oxidation reaction of malonie acid with bromate in the presence of cerium(m, IV) ions were studied quite thoroughly []-3]. Our earlier attempt [4] to carry out the periodic reaction in such systems by substituting cerium(HI, IV) ions with vanadium(IV, V) ions was not successful. However, it was found that addition of vanadium(IV) to the oscillating chemical systems, catalysts of which are ceriam(III, IV)ions or ferroin,* affects significantly the character of oscillations. Characteristics of oscillating reactions with participation of vanadium(IV, V) ions were obtained in this research and the probable mechanism of the joint effect of vanadium(IV, V) ions and ferroin was examined qualitatively. The optical density [a light filter with a region of transmission of 640-750 nm was used for the system containing cerium(HI, IV)], redox potential, and potential of the bromide-selectiv e electrode were recorded to observe the course of reaction using the earlier described apparatus [5] constructed on the basis of an instrument for automatic recording of optical density [6]. Recording of the changes in redox potential was carried out on a smooth platinum electrode and the bromide-ion concentration was recorded on a Radelkis bromideselective electrode. The reaction was run in a glass cell with a thickness of the absorbing layers of 3 cm and a volume of the reaction mixture of 14 ml with intense stirring and a constant temperature of 20  0.1~ Spectra of the colored compounds were taken on a Specord UV-Vis spectrophotomete r. Pure grade malonic acid was recrystallized before use from a 1:1 acetone:benzene mixture (mp 136~ The remaining reagents were either cp or analytical grade. The complex of iron(II) with 1,10-phenanthroline was prepared according to the instructions of [7]. The vanadyl sulfate solution was added to the reaction mixture containing ferroin both during oscillations and before their start. In the latter case this caused the appearance of an induction period, 4-6 min long, which was almost not observed in the absence of vanadium ions. The average period and average amplitudes of oscillation of optical density, redox potential, and potential of the bromide-selectiv e electrode were determined from the periods of the first 10 oscillations. It is seen from the dependence of these parameters on the concentration of vanadium ions in the system, presented in Table 1, that an increase in vanadium ion concentration leads to a significant decrease in the period of oscillation and amplitude of oscillattion of optical density. In this case the amplitude of oscillations of the redox potential and potential of the bromide-selectiv e electrode remains constant in the limits of measurement accuracy, due to the reproducibility of values of the measured quantities in parallel experiments.