A Kinetic Study of the Isotopic Exchange of Indium in Indium N-2-Hydroxyethylethylenediamine-N,N',N'-triacetate Complex in Water

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1) The kinetics of the isotopic exchange of the indium EDTA-OH complex with uncomplexed indium has been studied in neutral and basic solutions, with 114mIn as tracer. 2) The exchange rate is independent of the concentration of uncomplexed indium and proportional to that of the EDTA-OH complex, giving the relationship R=k·b. 3) In a basic solution buffered by barbiturate, p-hydroxybenzoate, or ammonia, the k value is proportional to the concentration of hydroxide ions and is little affected by the buffer. The Arrhenius activation energy is 25 kcal. per mol., and a mechanism involving the dissociation of hydroxo complex [InZ·OH]− as the rate-determining step was postulated. The exchange is accelerated by glycine. 4) In a neutral solution with a pH value below 8, the rate is small but measurable. It is independent of the pH value and is little affected by barbiturate or p-hydroxybenzoate, and the activation energy is 19 kcal. per mol. The dissociation of a mixed complex containing tartrate as one of the ligands, [InZ·C4H4O6]2−, appears to be the rate-determining step. Glycine accelerates the exchange reaction. 5) The feature of the isotopic exchange of the indium EDTA-OH complex is quite different from that of the EDTA complex; the former seems to be much more labile than the latter and similar gallium complexes.
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