Substitution Reactions of Cobaltic Complexes catalysed by Adsorption

Abstract

THE rate of the reduction of the complexes [Co(NH₃)₅ X] at the dropping mercury electrode depends on the nature of the supporting electrolyte and increases in the order: SO₄ = ≪ ClO₄− <NO³− <Cl−<Br− as is manifested by the shift of the half-wave potential of the reduction wave with the change of the supporting electrolyte. The halides Cl−, Br− (and under suitable conditions also I−) cause a further, quite different effect: at a certain concentration of the halide ion a new reduction wave appears which starts from the potential of the dissolution of mercury. The relative height of this wave (that is, the ratio of the positive wave to the total diffusion current) increases non-linearly with increasing concentration of the anion until all the complex is reduced in this positive wave (Fig. 1).