H2O/Triton X-100 solvent effect in the micellar catalysis of the aquation of tris-(3,4,7,8-tetramethyl-1, 10-phenanthroline)iron(II)

Abstract

The effect of triton X-100 micelles on the aquation of Fe(Me4phen)2+3 has been investigated with triton X-100 as solvent. In liquid triton X-100, over a range of [H2O]T(0.2–2.0 mol dm–3), significant rate enhancement factors of 35–140 are observed. Acid inhibits the rate of aquation at fixed [H2O]T. A mechanism based on effective solvent participation in a chemical environment similar to that in reversed micelles is proposed in liquid triton X-100 with dispersed water pockets. This mechanism predicts direct H2O substitutions into the coordination sphere of Fe(Me4Phen)2+3 in the highly polar water pockets or cavities where the FeII complex molecules are solubilized. Changes in the tumbling rate, mobility, structure, nucleophilicity and activity of water are suggested to account for the observed changes in the rate of aquation as a function of [H2O]T, in the peculiar chemical environment of the water pockets. All kψ–[H2O]T profiles are structured and exhibit maxima with kψ(max) shifted to progressively higher [H2O]T as the fixed concentration of [H+]T is increased.