KINETICS OF MONOMER-DIMER INTERCONVERSION OF IRON(3)-ETHYLENEDIAMINETETRAACETATE AND RELATED CHELATES

The kinetics of formation and decomposition of the Fe(III) dimers of EDTA, HEDTA, and CyDTA have been determined in aqueous solution by temperature-jump and stopped-flow methods. For the formation of the dimer, designated Fe2L2O, from the monomeric species, in labile equilibrium FeL(OH) and FeL(H2O), d[Fe2L2O]/dt = k2[FeL(OH)]2 + k12′[FeL-(H2O)] [FeL(OH)] – k21[Fe2L2O] – k21′[Fe2L2O] [H+], For the three systems the values of the rate constants at 25° and I = 1.0 M with NaNO3 are, respectively: k12 = 6.0 × 102, 9.0 × 102, and 90 M-1 sec-1; k12′ = 2.0 × 104, 6.0 × 104, and ~102 M-1 sec-1; k21 = 1.2, 4.0, and 9.0 sec-1; k21′ = 5.0 × 108, 3.0 × 106, and ~1010 M-1 sec-1. The values are discussed. © 1969, American Chemical Society. All rights reserved.