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

Abstract

Kinetics ef the substitution reactions ef the lead(ll) complexes of ethylenediamineN, N, N', N'-tetraacetate(EDTA), N-(hydroxyethyl)ethylenediamine-N, N', N'-triacetate(EDTAeOH), 1, 2-cyclohexanediaminetetraacetate(CyDTA) and diethylenetriamine-N, N, N', Nt', N"-pentaace-tate (DTPA) with gallium(III) In have been studiedover a pH range 2 0-4 0 at 200C and an ionic strength of O, 1 in the presence of an excess of lead(ll) ions.
The reacVtions were follow5d spectrophotometrically at the maximum absorPtion wavelengths of the lead complexes. The initialrate of the reaction (R) was expressed as
R=(k1+k4[Pb2+])/[H+]+(k2+k5/[Pb2+]+(k3+k6/[Pb2+][H+])[Pbx](Ga3+)
for the EDTA and EDTA e OH systems,
R=(k5+k6[H+])EPbX)[Ga3+]/[Pb2+]
for the CyDTA system, and
R=((k3+k6/[Pb2+])/[H+]+(k7+k8/[Pb2+]))[PbH2x](Ga3+)
for the DTPA system.
Contribution of each reaction path to the over-all rate of the reaction was estimated. The reactions for the EDTA, EDTAeOH and DTPA systems seemed to proceed through both stepsforming binuclear intermediate complexes PbXtGa and the dissociative paths in wbich the rapid dissociitive equilibria of lead complexes proceeded to form the gallium complexes, and the reaction for the CyDTA system proceeded through the disseciativepaths.
In addition, sinde it was estimated that in the dissociative path the reaction. s-pr-o-ggedeq through the bath involving GaOH2', the rate constants for the formation of G4X. GeHXAand GaH, X couldM be calculated For EDTA, EDTA.OH orCyDTA kG.x w-as 1-3xIP, 1, 5x196 gr 2.7x107mo1-1 l sec-1, and kG0Hx was 1.0x10, , 7, 8x103 r 2 9x10 mo1-1 se-1 espectively and for DTPA kgx or kG H2x was 2.4x106 or 4, 0x104 mor1, 1 sec-1 again respectively.