A Pulse Radiolysis Investigation of the Reactions of BrO2. with Fe(CN)64-, Mn(II), Phenoxide Ion, and Phenol

Article abstract of DOI:10.1021/j100210a040

The single-electron reductions of BrO2^. by Fe(CN)6^4-, phenoxide ion, Mn(II), and phenol have been investigated.The BrO2^. was produced by pulse radiolysis of aqueous solutions of BrO3^- which also contained one of these reductants.All experiments were carried out at pH 6-12.The reductions by Fe(CN)6^4- and phenoxide ion were rapid and clean and led to the products Fe(CN)6^3- and phenoxy radical.The rate constants for these reductions were found to be, respectively, (1.9+/-0.1)E9 and (2.6+/-0.2)E9 M^-1 s^-1.The reductions of BrO2^. by Mn(II) and phenol were found to be much slower as well as more complex than the reductions by Fe(CN)6^4- and phenoxide ion.The products were, as expected, Mn(III) and phenoxy radical.However, there was a component of BrO2^. reduction by Mn(II) whose rate did not depend upon .Furthermore, the rate of BrO2^. reduction by phenol did not depend at all upon the concentration of phenol.It is suggested that these slower reductions were complicated by the well-known dimerization equilibrium between BrO2^. and Br2O4.If the rate of reduction of this dimer by Mn(II) or phenol is comparable to or faster than the rate of its return to BrO2^., then the dimerization process itself will become partially or completely rate determining; thus the less than expected dependence of the rates of these reductions on reductant concentrations may be rationalized.Regardless of the exact mechanism of the process, it was shown that the reduction of BrO2^. by Mn(II) and phenol proceeds with the stoichiometry and overall time scale inferred from studies of the reduction of BrO3^- by some weak metal-ion reductants and of catalyzed (Belousov-Zhabotinsky reaction) and uncatalyzed bromate-driven chemical oscillators.