A very small kinetic salt effect for the reactions of CuEDTA with the hydrated electron

The reactivity of some metal ions towards the hydrated electron depends strongly on the ligands. Most of the aquo complexes are highly reactive and the rate constants approach the diffusion controlled limit. This also holds for the complex of Cu(II) with ethylenediaminetetraacetate, CuEDTA2-. This complex is known to be labile towards substitution: one coordination position can be occupied by NH3, ethylenediamine, CN-, or OH-. In this study the influence of the equilibrium: CuEDTA2- + H2O = CuEDTA(OH)3- + H+ on the reaction rate with e-sub(aq) has been measured for a series of ionic strengths. The equilibrium constant is defined by: Ksub(CuEDTA(OH)) = [CuEDTA(OH)3-][H+]/[CuEDTA2-]. Literature values for this constant are pKsub(CuEDTA(OH)) = 11.6 (μ = 1) and pKsub(CuEDTA(OH)) = 11.4. Consequently measurements were made in the pH range 7.5 to 11 and above pH 12. Experimental details are given. Kinetic salt effects for the reactions of e-sub(aq) with CuEDTA2- and CuEDTA(OH)3- are shown. The results are discussed. (U.K.)