RATE CONSTANTS FOR REACTIONS BETWEEN IODINE-CONTAINING AND CHLORINE-CONTAINING SPECIES - A DETAILED MECHANISM OF THE CHLORINE DIOXIDE CHLORITE-IODIDE REACTION/

The chlorite-iodide reaction is unusual because it is substrate-inhibi ted and autocatalytic. Because analytically pure ClO2- ion is not easi ly 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 p arts are the (a) chlorine dioxide-iodide, (b) chlorine(III)-iodide, (c ) chlorine(III)-iodine, and (d) hypoiodous and iodous acid disproporti onation reactions. The overall reaction has been studied experimentall y and by computer simulation by breaking it down into a set of kinetic ally active subsystems and three rapidly established equilibria: proto nations of chlorite and HOI and formation of I-3(-). The subsystems wh ose kinetics and stoichiometries were experimentally measured, remeasu red, or which were previously experimentally measured include oxidatio n 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 determine d by sensitivity analysis and parameter fitting of differential equati on systems. Rate constants determined for simpler reactions were fixed in the more complex systems. A 1S-step model with the three above-men tioned rapid equilibria fits the overall reaction and all of its subsy stems 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 degrees C. The derived model wit h all experimentally determined rate and equilibrium constants fits bo th the overall reaction and all of its subsystems within 1% relative a ccuracy.