Abstract
In order to study the chemical oscillatory behavior and mechanism of a new chlorine dioxide-iodide ion-methyl acetoacetate reaction system, a series of experiments were done by using UV-Vis and online FTIR spectrophotometric method. The initial concentrations of methyl acetoacetate, chlorine dioxide, potassium iodide, and sulfuric acid and the pH value have great influence on the oscillation observed at wavelength of 289 nm. There is a preoscillatory or induction period, and the amplitude and the number of oscillations are associated with the initial concentration of reactants. The equations for the triiodide ion reaction rate changing with reaction time and the initial concentrations in the oscillation stage were obtained. Oscillation reaction can be accelerated by increasing temperature. The apparent activation energies in terms of the induction period and the oscillation period were 26.02 KJ/mol and 17.65 KJ/mol, respectively. The intermediates were detected by the 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.
Highlights
Chemical oscillations are systems of chemicals that exhibit time-based fluctuations when they are far from equilibrium
In previous papers we have studied the chlorine dioxideiodine-malonic acid-sulfuric acid oscillation reaction [22] and sodium chlorite-iodine-ethyl acetoacetate oscillation reaction [23]
In order to investigate the influence of the reactant concentrations on the oscillation, experiments were carried out by fixing [H2SO4]0 = 3.50 × 10−3 mol/L and [methyl acetoacetate (MAA)]0 = 6.29 × 10−3 mol/L keeping the molar ratio of [ClO2]0/[KI]0 = 0.115, and changing the initial concentrations of chlorine dioxide and potassium iodide at the same time
Summary
Chemical oscillations are systems of chemicals that exhibit time-based fluctuations when they are far from equilibrium. Illumination of the chlorine dioxide-iodine-malonic acid reaction with visible light suppresses oscillations and shifts the steady state of the reaction to lower concentrations of iodide ions [16]. In the system with starch, illumination results in a strong decrease of the steady-state concentration of the triiodide-starch complex They suggested a simple mechanism, in which iodine atoms produced by photodissociation of molecular iodine initiate reduction of chlorine dioxide to chlorite and oxidation of iodide ions to iodine. In order to study the chlorine dioxide-iodide-methyl acetoacetate oscillator reaction better, it is necessary to investigate all of the factors that influence the reaction Taking into account these factors, we found that oscillations can occur at 289 nm for the triiodide ion.
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