NONMETAL REDOX KINETICS - HYPOBROMITE AND HYPOBROMOUS ACID REACTIONS WITH IODIDE AND WITH SULFITE AND THE HYDROLYSIS OF BROMOSULFATE

The pulsed-accelerated-flow method is used to study the reactions of OBr- with I- and with SO3(2-) (25.0-degrees-C, mu = 0.50 M). Pseudo-first-order rate constants for the OBr- with I- reaction are measured in the range 5930-12900 s-1. The even faster reaction between OBr- and SO3(2-) is studied under second-order conditions. The proposed mechanism includes parallel paths with Br+ transfer to the nucleophile (X = I-, SO3(2-)) via solvent-assisted reaction with OBr- as well as diffusion-controlled reactions between [GRAPHICS] HOBr (pK(a) = 8.80) and these nucleophiles. The second-order rate constants (M-1 s-1) are as follows: k(OBr) = 6.8 (+/- 0.4) x 10(5) and k(HOBr) = 5.0 (+/- 0.3) x 10(9) with I-; k(OBr) = 1.0 (+/- 0.1) x 10(8) and k(HOBr) = 5 (+/- 1) x 10(9) with SO32-. The intermediate IBr(aq) is unstable with respect to hydrolysis, and it readily forms OI-. The BrSO3- that is formed in the OBr- and HOBr reactions with SO32- hydrolyzes with a rate constant k(h) = 230 (+/- 20) s-1 at 0.0-degrees-C to give SO42- and Br-. The relative hydrolysis rate constants (25-degrees-C) for the halosulfates are in the order BrSO3- >> ISO3- congruent-to ClSO3- >> FSO3-.