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

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[CuI]/dt =kaKa[Cu(Bipy)2+2]+kbKb[Cu(Bipy)2+2][Cu(Bipy)+2]/[H+]+kcKc[Cu(Bipy)+2][H+]–kd[Cu(Bipy)+2]PO2.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.