Substitution Reactions of Some Lead(II)-Polyamine-N-polyacetate Complexes with Yttrium(III) Ion

Abstract

Kinetics of the substitution reactions of the lead (II) complexes of ethylenediamine-N, N, N', N'-tetraacetic acid (EDTA), N- (hydroxy ethyl) ethylenediamine-N, N', N'-triacetic acid (EDTAH), 1, 2-cyclohexanediamineteraacetic acid (CyDTA) and dietylenetriamine-N, N, N', N", N" -pentaacetic acid (DTPA) with yttrium (W) ion have been studied in the pH range 2.5-, 5.6, at 20° C and an ionic strength of 0.1 in the presence of excess lead (II) ion.
The inital rate equations of the forward and reverse reactions were obtained by observing the change in absorbance. Contribution of each reaction path way to over-all rate of the reaction was estimated. The reactions for the EDTA, EDTAH and DTPA systems seemed to proceed through two path ways: (1) forming binuclear intermediate complexes and (2) dissociating metal complexes. In the forward reactions the rapid dissociation of lead complexes precedes the formation of yttrium complexes, and in the reverse reactions the dissociation of yttrium complexes is the rate-determining step. The reactions for the CyDTA systems proceed merely through the dissociation of the metal complexes.
The rate constants for the formation of YHX (kyllx) were found to be 1.0 x109, 1.9 x 107, 2.4 X 107 and 4.3 x 10mol-sec for EDTA, EDTA H, CyDTA and DTPA (H, X), respec- tively, where HnX represents the polyamine-N-polyacetic acids.