Outer sphere catalysis of cerium(IV)-iron(II) electron transfer reactions by pyridine derivatives

Abstract

The kinetics of the electron transfer reactions between Ce^IV and the Fe^II compounds [Fe(H₂O)₆]²⁺ and [Fe(phen)₃]²⁺ in sulphuric acid media in the presence and absence of several aromatic amines as possible electron transfer catalysts, has been investigated. In uncatalyzed as well as in catalyzed reactions two Ce^IV species, viz. [Ce(SO₄)₂] and [Ce(SO₄)₃]^2–, participated. The experimental data for the catalyzed reaction paths could be explained by a mechanism involving a bimolecular reaction between Fe^II and an ion pair consisting of [Ce(SO₄)₃]^2– and a protonated catalyst molecule, and/or a reaction via a termolecular collision of [Ce(SO₄)₂], Fe^II, and catalyst. The catalyzed reaction paths were analyzed on the basis of recently developed quantum mechanical theories for bridge electron transfer reactions.