Substitution Reactions of Some Lead(II)-Polyamine-N-polyacetate Complexes with Aluminium(III) Ions

Abstract

Kinetics of the substitution reactions of lead (II) complexes of ethylenediaminetetraacetate (edta) N- (2-hydroxyethyl) ethylenediamine-N, N', N'-triacetate (edtaoh), 1, 2-cyclohexanediaminetetraacetate (cydta), and diethylenetriamine-N, N, N', N", N"-pentaacetate (dtpa) with aluminium (f) ions have been studied in the pH range 2.4∼4.4, at 20° C, with an ionic strength of 0.1, and in the presence of excess lead(II) ions ((0.2∼2.0) x 10^-4 moledm^-3). Similarly, the reverse reactions have also been kinetically studied in the presence of excess aluminium(II) ions (1.0 X 10^-3 mol dm^-3).
The forward reactions proceed through the paths involving the species of Al0H²⁺ and Al₂(OH)₂⁴⁺ in the case of edta and edtaoh in the pH range 2.6-4.4. The initial rate equations of the forward and reverse reactions have been obtained by observing the change in absorbance in the region 240∼250 nm. Contribution of each reaction path to the over-all rate of the reactions was estimated. The forward reactions seem to proceed merely through the dissociative path liberating the ligands from the metal complexes in the case of edta, edtaoh and cydta and in the case of dtpa mainly through the dissociative path. The reverse reactions in the case of edta, edtaoh and cydta seem to proceed mainly through the dissociative path, but also proceed slightly through the path forming binuclear intermediate complexes.