Kinetics of the Oxidation of Bromopyrogallol Red by Nitrite Ion in Aqueous Acidic Medium

The kinetics of the electron transfer reaction between Bromopyrogallol (BPR^2-) and nitrite ion in aqueous acidic solution has been studied in the acid range 0.1 × 10^-4 ≤ [H⁺] ≤ 2 × 10^-4 mol dm^-3, ionic strength 0.01 ≤ ≤ 0.18 mol dm^-3 (NaCl) and T = 29 ± 1.°C. The reaction shows a first order dependence on oxidant and reductant concentration respectively. The rate of the reaction increases with increase in [H⁺]. Plot of k₂ versus [H⁺] was linear with a positive intercept. The overall reaction conforms to the rate law: -d[BPR^2-]/dt = (a + b[H⁺])[BPR²][NO₂^-]. The stoichiometry of the reaction is 1:1 (BPR^2- : NO₂^-). Added anions had no effect on the rate of the reaction. The results of spectroscopic investigation indicate that no intermediate complex is probably formed in the course of this reaction. The reaction is believed to proceed via the outersphere mechanistic pathway.