Kinetics and Mechanism of [Fe (bipy)(3)](2+) and [BrO3-] System in Aqueous Acidic Medium

摘要

The kinetics of the oxidation of tris (2,2'-bipyridine) iron(II) ([Fe(bipy)(3)](2+)) by bromate ion (BrO3-) in aqueous medium have been investigated. The reaction was probed spectrophotometrically in the pH range 3.5-5.0, and from 0.01 to 0.1 mol/dm(3) ionic strength. The kinetic runs were pursued to more than two half lives of the reaction. The pseudo first order rate constant was found independent of the concentration of tris (2, 2'-bipyridine) iron (II), and increases with increasing concentration of bromate ion in the reaction mixture. Protonation of BrO3- in the acidic medium yields monoprotonated (HBrO3) and diprotonated (H2BrO3+) species. The rising figure of the rate constant upon lowering the pH refers to the involvement of protonated species in the rate-determining step. A rise in the value of the rate constant with increasing ionic strength implies, however, the diprotonated species, H2BrO3+, as the reactive species among the two competing. Involvement of the other Br(V) species results in a complex reaction pathway, consequently. The rate law is suggested as follows: