Cinétique et mécanisme des réactions bromate–chlorite et bromate – dioxyde de chlore

Abstract

In an acidic solution, containing initially chlorous acid and bromate in excess, two consecutive reactions are observed, the oxidation of chlorous acid to chlorine dioxide followed by the oxidation of chlorine dioxide: BrO3− + 4ClO2 + 2H2O = 4ClO3− + 3H+ + HOBr. The kinetics of this reaction has been studied and a mechanism proposed. It agrees with the one accepted for the related reaction between bromate and Ce(III). Extended by reactions of chlorous acid, the mechanism reproduces the experimental curves of chlorine dioxide evolution in chlorous acid – bromate solutions. The values of the equilibrium and kinetic constantes are discussed.

Kinetics and mechanism of formation of chlorate ion from the hypochlorous acid/chlorite ion reaction at pH 6-10

“…Our results are consistent with their observations. However, the results presented here are in contrast to the published facts (17,20,21) for the H0C1/HC102 reaction at pH <5.0, where it is reported that the reaction produces both chlorine dioxide and chlorate ion. In this context, from the earlier reports, it is not clear whether the two products are formed in parallel or consecutive reactions.…”

“…However, no detailed mechanistic information appears to be available in the literature for reactions 1 and 4. Our observation that the contribution of reaction 1 increases with decreasing pH values in the reaction between free chlorine and C102' in the pH 6.4-10.0 range is consistent with previous reports (8,20,21,31) that C102 formation is dominant only at low pH values.…”

“…This means that the production of chlorine dioxide and chlorate ion are independent of each other in solutions above pH 6. In the experiments reported here, no detectable chlorine dioxide formation was observed during the latter part of the reaction even in the presence of hypochlorous acid/ hypochlorite ion and chlorite ion, which were continuing to react to form chlorate ion at pH 6.4-10.0. This suggests that the observed C102 formation at the initial stage of the reaction was caused by rapid reactions at concentration gradients due to incomplete mixing and/or by the adventitious presence of impurities such as metal ions (17,20,21).…”

Bromite Ion Catalysis of the Disproportionation of Chlorine Dioxide with Nucleophile Assistance of Electron-Transfer Reactions between ClO2 and BrO2 in Basic Solution

“…Bromine dioxide is a highly reactive compound that is capable of disproportionating to form BrO 2 - and BrO 3 - . − However, this does not take place because the concentration of BrO 2 is very low compared to ClO 2 so that the reactions in eqs 3 and 4 generate ClO 3 - and regenerate BrO 2 - . The reaction between BrO 2 and ClO 2 has been proposed as an intermediate step in the reduction of bromate ion by chlorous acid. , The rate constant for the BrO 2 /ClO 2 reaction at 1.0−2.0 M [H + ] has been estimated to be 1.2 × 10 5 M -1 s -1 . Thermodynamically, eqs 3 and 4 are very favorable and overcome the unfavorable step in eq 2.…”

Kinetics and Mechanism of the Chlorite–Periodate System: Formation of a Short-Lived Key Intermediate OClOIO3 and Its Subsequent Reactions

“…As a result the last couple of decades have witnessed intense studies of various oxyhalogen-based systems via monitoring the reactants, intermediates, and/or products by different spectroscopic techniques such as UV–vis and stopped-flow technique in order to establish reliable kinetic models and to obtain thorough insight into their mechanisms. The list, of course, does not end here; further examples of such systems as the bromate–chlorite, hypochlorous acid–chlorite, chlorate–bromide, chlorate–chloride, iodide–iodate, and periodate–bromide reactions may also be provided after a survey of the literature. Checking the reported mechanisms of these systems has revealed that crucial short-lived intermediates (halogen oxides with different compositions) are considered to be involved for explanation of the kinetic behaviors.…”