Kinetics and Mechanism of the Chlorate–Bromide Reaction

Abstract

The chlorate-bromide reaction, ClO3(-) + 6Br(-) + 6H(+) → 3Br2 + Cl(-) + 3H2O, was followed at the Br3(-)/Br2 isosbestic point (446 nm). A fifth-order rate law was found: (1)/3 d[Br2]/dt = k[ClO3(-)][Br(-)][H(+)](3) (k = 5.10 × 10(-6) s(-1) L(4) mol(-4)) at 25 °C and I = 2.4 mol L(-1). At high bromide concentrations, the bromide order becomes close to zero, indicating a saturation profile on bromide concentration, similar to the chloride saturation profile observed in the chlorate-chloride reaction. A mechanism is proposed that considers the formation of the intermediate BrOClO2(2-), similar to the intermediate ClOClO2(2-) proposed in the mechanism of the chlorate-chloride reaction.

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

“…Step is the other rate-determining step of the proposed model, producing OClOIO 3 , a key intermediate of the reaction. Similar oxyhalogen intermediates have already been well-established in the case of the Dushman reaction, as well as those of the chlorite–hypochlorous acid, chlorate–chloride, periodate–bromide, and chlorate–bromide reactions. By an analogy, we therefore propose here OClOIO 3 .…”

“…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.…”

“…Cl 2 O 3 was established as a key intermediate in the decomposition of chlorous acid in driving the reaction to stoichiometrically different pathways . Very recently mixed halogen oxides (BrIO 3 and BrOClO) were reported to participate in the periodate–bromide and chlorate–bromide reactions. , …”

Kinetics and Mechanism of the Chlorate–Nitrous Acid Reaction

“…The model results were compared to the absorbance versus time curves obtained experimentally using different concentration of the reactants. The entire procedure is analogous to that used in the similar kinetic study of chlorate–bromide reaction made recently by our group …”

“…The entire procedure is analogous to that used in the similar kinetic study of chlorate−bromide reaction made recently by our group. 16 ■ RESULTS AND DISCUSSION…”