Experimental Study of a Closed System in the Chlorine Dioxide–Iodine–Ethyl Acetoacetate–Sulfuric Acid Oscillation Reaction by UV-vis and Online FTIR Spectrophotometric Methods

Abstract

The appearance of oscillations for the closed system ClO2–I2–ethyl acetoacetate depends critically on the pH in the absence of sulfuric acid, and was investigated by determining changes in the absorbance of $\mathrm{I}_{3}^{ -}$ with reaction time at the wavelength 280 nm. The pH should be 2.2–3.8 for this reaction. The initial concentrations of ethyl acetoacetate, chlorine dioxide, iodine and sulfuric acid have great influences on the oscillations observed at wavelengths of 280 nm or 350 nm. The oscillations at 280 nm occur as long as the reactants are mixed. However, at 350 nm the oscillation is preceded by a pre-oscillatory or induction period. The oscillation curve is more regular and smooth at 350 nm than that at 280 nm. The amplitude and the number of oscillations are associated with the initial concentration of each reactant. (1) The higher the initial concentration of ethyl acetoacetate, the greater is the amplitude while the number of oscillations becomes smaller. The amplitude is small at the beginning stage but increases with reaction time. An opposite influence exists for chlorine dioxide. Finally, the oscillation suddenly ceases. (2) When the initial concentration of iodine is higher, the amplitude is small at the beginning stage but then increases with reaction time. When the initial concentration of iodine is lower, the amplitude is large at the beginning stage and then decreases with reaction time. An opposite influence exists for sulfuric acid. Equations for the triiodide ion reaction rate were obtained as functions of reaction time and initial concentrations at the oscillation stage. The intermediates were detected by online FTIR analysis. Based upon the experimental data in this work and in the literature, a plausible reaction mechanism was proposed for the oscillation reaction.