Spectrophotometric investigations in aqueous solution at elevated temperatures. Kinetics of the reduction of copper(II) to copper(I) at 473 K in aqueous solution in the presence of 2,2′-bipyridyl

Abstract

The kinetics of reduction of the aqueous bis(2,2′-bipyridyl) copper(II) cation by water to the corresponding copper(I) cation have been investigated spectrophotometrically at 473 K in the concentration ranges (0.2–2.5)× 10^–3 mol dm^–3 copper perchlorate, (0.2–1.8)× 10^–2 mol dm^–3 2,2′-bipyridyl and (0–2)× 10^–2 mol dm^–3 perchloric acid.

The results have been shown to be consistent with the following rate law for the reaction: d[Cu^I]/dt =k_aK_a[Cu(Bipy)²⁺₂]+k_bK_b[Cu(Bipy)²⁺₂][Cu(Bipy)⁺₂]/[H⁺]+k_cK_c[Cu(Bipy)⁺₂][H⁺]–k_d[Cu(Bipy)⁺₂]P_O2.

At low acid concentrations the reaction proceeds by two pathways: one independent of the copper(I) species and the other autocatalysed by them in a mechanism exhibiting inverse dependence on the acid concentration. A third, acid catalysed pathway becomes significant at greater acid concentrations. In all cases the results are consistent with a rate-determining step involving the homolytic cleavage of copper–oxygen bonds. The relative amounts of the copper(I) and copper(II) species at equilibrium are strongly dependent on the concentration of oxygen initially present.