Reduction of bromine(V) by tris(1,10-phenanthroline)-iron(II) in aqueous sulfuric acid

The kinetics and mechanism of the reduction of bromate by Fe(phen) 3 2+ depend upon the concentration ratio of the reactants. At [Fe(phen) 3 2+ ]≶[BrO 3 − ] the rate-determining step is the dissociation of Fe(phen) 3 2+ ; at [Fe(phen) 3 2+ ]≪[BrO 3 − ] the reaction is autocatalytic. A duality in the behaviour of Fe(phen) 3 2+ is pointed out.