Kinetics of electrophilic substitution of erbium(III) by ytterbium(III) in an aqueous solution of ethylenediaminetetraacetate

Abstract

1. Electrophilic substitution in ethylenediaminetetraacetates of rare-earth(III) elements, independently of the nature of the leaving cation, is accomplished according to two competing mechanisms: an acid dissociation mechanism and an associative mechanism. 2. Exhange according to the acid dissociation mechanism is catalyzed by protons; and depending on the acidity of the medium, singly and doubly protonated intermediate complexes are formed. 3. The associative exchange mechanism predominates in less acid media and is realized by means of formation of intermediate binuclear complexes. The limiting step for exchange according to an associative mechanism is the breaking of the metal-nitrogen bond, formed by the leaving cation and the ligand in the intermediate binuclear complex.