The reaction of aquomanganese(III) ions with bromide ions in perchlorate media

Abstract

The rapid reaction of Mn(III) ions with bromide ions is retarded by decrease in [HClO₄]. Mn(II) and molecular bromine are the final products, with Δ[Mn(III)]/Δ[Br^–]= 1·0 and Δ[Mn(III)]/Δ[Br₂]= 0·5, and the reaction proceeds by way of bromine atoms. At high [Br^–], the initial rate is first-order in [Mn(III)] and second-order in [Br^–]; at low [Br^–], the initial rate is first-order in [Mn(III)] and first-order in [Br^–]. The kinetics show that the hexa-aquomanganese(III) ion is reactive and the hydroxopenta-aquomanganese(III) ion is unreactive towards Br^– ions, and the electron-transfer proceeds in the inner sphere of Mn³⁺_aq. The reaction is retarded by the addition of cations owing to the formation of inert 1:1 cation + bromide ion complexes.