Kinetics of the Reduction of Di-µ-oxo-Tetrakis (1,10-Phenanthroline)-Dimanganese (III,IV) Perchlorate by DL-Methionine in Acid Solution

Abstract

The kinetics of reduction of di-µ-oxo-tetrakis(12,10-phenatroline)-dimanganese (III,IV) perchlorate by DL-menthionine in acid solution as been studied. The data are consistent with the rate law: with a = 4.75 x 10-5 s-1, b = 1.55 x 10-3 M-1s-1, Ea = 74.1 kJ mol-1, H# = 72.0 kJ mol-1 and S# = -293 J K-1 mol-1 at I = 0.50 M (NaCl), T = 29.0oC and λ = 555 nm. There is no evidence for the formation of an intermediate complex of significant stability and free radicals are unimportant in the reaction. The reduction is rationalized in terms of a proton coupled electron transfer pathway (PCET).