Kinetic Study of the Reduction of Bromate Ion by Tris(1,10-Phenanthroline)Iron(II) and Aquoiron(II) Ions — Implication for the Bromate-Gallic Acid Oscillating Reaction

The kinetics of the bromate oxidation of tris(1,10-phenanthroline)iron(II) (Fe(phen)₃²⁺) and aquoiron(II) (Fe²⁺ (aq)) have been studied in aqueous sulfuric acid solutions at μ = 1.0M and with Fe(II) complexes in great excess. The rate laws for both reactions generally can be described as -d Fe(II)]/6dt = dBr^?]/dt = kFe(II)] BrO^?₃] for H⁺]₀ = 0.428–1.00M. For BrO^?₃]₀ = 1.00 × 10^?4M. Fe²⁺]₀ = (0.724–1.45)x 10^?2 M, and H⁺]₀ = 1.00M, k = 3.34 ± 0.37 M^?1s^?1 at 25°. For BrO^?₃]₀ = (1.00–1.50) × 10^?4M, Fe²⁺]₀ = 7.24 × 10^?3M (phen]₀ = 0.0353M), and H⁺]₀ = 1.00M, k = (4.40 ± 0.16) × 10^?2 M^?1s^?1 at 25°. Kinetic results suggest that the BrO^?₃-Fe²⁺ reaction proceeds by an inner-sphere mechanism while the BrO^?₃-Fe(phen)₃²⁺ reaction by a dissociative mechanism. The implication of these results for the bromate-gallic acid and other bromate oscillators is also presented.