Abstract
The kinetics of the disproportionation reaction of bromine(III), 2Br(III) -* Br(I) + Br(V), was studied in phosphate buffer, in the pH range 5.9-8.0, by monitoring optical absorbance at 294 nm using stopped-flow. The dependences on <Jh+ and [Br(III)] were of order 1 and 2, respectivley, and no dependence on [Br~] was found. The reaction was also studied in acetate buffer, in the pH range 3.9-5.6. Within experimental error, no evidence was found for a direct reaction between two 03~ ions. This study yields rate constants 39.1 ± 2.6 M"1 sTM1 for the reaction HBrC>2 + BrCV -* HOBr + Br03 and 800 ± 100 M-1 sTM1 for the reaction 2HBr03 -* HOBr + Br03" + H+ and an equilibrium quotient for HBr03 «=* H+ + Br03" of 3.7 ± 0.9 X Kh4 M (pATa = 3.43) at ionic strength 0.06 M and 25.0 ± 0.1 °C. The bromous acid dissociation constant is essentially identical to the value previously obtained from a kinetics study of the bromine(III)-I~ reaction (/. Phys. Chem. 1992, 96, 6861).