Rate Constants for Reactions between Iodine- and Chlorine-Containing Species:  A Detailed Mechanism of the Chlorine Dioxide/Chlorite-Iodide Reaction

Abstract

The chlorite-iodide reaction is unusual because it is substrate-inhibited and autocatalytic. Because analytically pure ClO2 - ion is not easily prepared, it was generated in situ from the rapid reaction between ClO2 and I-. The resulting overall reaction is multiphasic, consisting of four separable parts. Sequentially, beginning with mixing, these parts are the (a) chlorine dioxide-iodide, (b) chlorine(III)-iodide, (c) chlorine(III)-iodine, and (d) hypoiodous and iodous acid disproportionation reactions. The overall reaction has been studied experimentally and by computer simulation by breaking it down into a set of kinetically active subsystems and three rapidly established equilibria: protonations of chlorite and HOI and formation of I3 -. The subsystems whose kinetics and stoichiometries were experimentally measured, remeasured, or which were previously experimentally measured include oxidation of iodine(−1,0,+1,+3) by chlorine(0,+1,+3), oxidation of I- by HIO2, and disproportionation of HOI and HIO2. The final mechanism and rate constants of the overall reaction and of its subsystems were determined by sensitivity analysis and parameter fitting of differential equation systems. Rate constants determined for simpler reactions were fixed in the more complex systems. A 13-step model with the three above-mentioned rapid equilibria fits the overall reaction and all of its subsystems over the range [I-]0 < 10-3 M, [ClO2 -]0 < 10-3 M, [I-]0/[ClO2 -]0 = 3−5, pH = 1−3.5, and 25 °C. The derived model with all experimentally determined rate and equilibrium constants fits both the overall reaction and all of its subsystems within 1% relative accuracy.

Modelling iodide – iodate speciation in atmospheric aerosol: Contributions of inorganic and organic iodine chemistry

“…Aqueous phase iodine reactions. Differences to the mechanism used by Vogt et al (1999) and von Glasow et al (2002a) Lengyel et al (1996) I 18 HIO 2 +HOBr−→IO − 3 +Br − +2H + 2 1.0×10 6 Chinake and Simoyi (1996) Glasow et al (2002a) m, n give the order of the reaction. k 0 is the reaction rate constant for 298 K. K 0 is the equilibrium constant for 298 K. * Special rate law for reactions controlled by diffusion as explained in the text.…”

Diffusive Instabilities and Chemical Reactions

“…This reaction belongs to the family of the CIMA and CDIMA reactions that lead to Turing patterns, as seen above. It is a "minimal" nonlinear chemical system [Epstein & Orbán, 1985;De Kepper et al, 1990] for which a very comprehensive kinetic mechanism has been proposed [Lengyel et al, 1996] which quantitatively accounts for the batch and CSTR dynamical behaviors of the reaction. This prototypic bistable reaction system is less complex and has a much better established kinetic mechanism than that of the bistable FIS reaction which has led to the observation of labyrinthine and other interacting front patterns [Lee et al, 1993;Li et al, 1996] in a disc OSFR slightly more intricate than the one described in Fig.…”

Aqueous photochemical reactions of chloride, bromide, and iodide ions in a diode-array spectrophotometer. Autoinhibition in the photolysis of iodide ions

“…The formation equilibrium constants of trihalide ions (eqn (1)) have been reported in previous studies. 34,35 …”

“…34,35 For Cl − , K Cl is too low to be determined by the same method as the solubilities of chloride salts are insufficient to obtain high enough free chloride ion concentrations. This fact led us to conclude that K Cl < 1 M −1 .…”