Kinetics and mechanism of the oxidation of tris(1,10-phenanthroline)iron(II) by peroxomonosulphate (oxone) ion

The oxidation of tris(1,10-phenanthroline)Fe(II) with peroxomonosulphate (oxone) ion is first order with respect to both the substrate and the oxidant. The rate is accelerated by the alkali metal ion and the plot of k0 against [M+] indicates that a part of the rate is independent of [alkali metal ion] where k0 is the true rate constant for the reaction and is equal to kobs − kh. The rate constant kh refers to the hydrolysis of [Fe(phen)3]2+ ion. It is explained by assuming the formation of an ion pair between M+ and SO52-ions whereas a similar ion pair between M+ and HSO5- ions is not favoured in view of the slope value of the Davies plot for the effect of ionic strength which has a slope of −2.02. There is spectral evidence for the formation of an intermediate and accordingly the intermediates [Fe(phen)3⋯HSO5]+ and [Fe(phen)3⋯M⋯SO5]+ are assumed to be formed in the proposed mechanism where M+ ion acts as a bridge. The disproportionation of the intermediates is considered to be rate determining. The H+ ions retard the rate and the plot of k0[H+] against [H+] has an intercept on the rate ordinate.

The oxidation of tris(1,10-phenanthroline)Fe(II) with peroxomonosulphate (oxone) ion is first order with respect to both the substrate and the oxidant. The rate is accelerated by the alkali metal ion and the plot of k0 against [M+] indicates that a part of the rate is independent of [alkali metal ion] where k0 is the true rate constant for the reaction and is equal to kobs − kh. The rate constant kh refers to the hydrolysis of [Fe(phen)3]2+ ion. It is explained by assuming the formation of an ion pair between M+ and SO52- ions whereas a similar ion pair between M+ and HSO5- ions is not favoured in view of the slope value of the Davies plot for the effect of ionic strength which has a slope of −2.02. There is spectral evidence for the formation of an intermediate and accordingly the intermediates [Fe(phen)3⋯HSO5]+ and [Fe(phen)3⋯M⋯SO5]+ are assumed to be formed in the proposed mechanism where M+ ion acts as a bridge. The disproportionation of the intermediates is considered to be rate determining. The H+ ions retard the rate and the plot of k0[H+] against [H+] has an intercept on the rate ordinate.Figure optionsDownload as PowerPoint slide