Kinetics and Mechanism of the Oxidation of Iminodiacetate, Nitrilotriacetate and Ethylenediaminetetraacetate by trans-Cyclohexane-1,2-diamine-N,N,N',N'-tetraacetatomanganate(III) in Aqueous Media

Article abstract of DOI:10.1039/DT9910002729

Kinetic studies of the oxidation of iminodiacetate (ida), nitrilotriacetate (nta) and ethylenediaminetetraacetate (edta) by trans-cyclohexane-1,2-diamine-N,N,N',N'-tetraacetatomanganate(III), III(cdta)>(1-), have been made in aqueous solution in the range pH 3.0-10.0 with varying reductant concentrations at constant ionic strength, I = 0.50 mol dm^-3 (NaClO4), and temperature, 30 deg C.All the reactions are first order in complex and reductant concentration, and follow the general rate law -dIII>/dt = k_obsIII> = (k_d + k_s)III>, where k_d denotes the autodecomposition rate of the complex, k_s the electron-transfer rate and R is the reductant irrespective of the nature and type of the reacting species.The complex III(cdta)>(1-) showed an interesting behaviour in acidic and alkaline media.For ida oxidation both the aqua- and hydroxo-forms of the complex are reactive and an inner-sphere mechanism has been proposed.However, for nta and edta oxidations, the aqua form is the sole reacting species and an outer-sphere mechanism has been proposed.The rate parameters and proton equilibrium constant of the complex and reductants were obtained by fitting of the experimental data by appropriate rate equations using computer-fit programs.Thus the reactivities of all the species of the polycarboxylates available in the reaction solutions have been evaluated individulally.The reactivity orders are Hida(1-) < ida(2-), H2nta(1-) < Hnta(2-) < nta(3-) and H3edta(1-) < H2edta(2-) < Hedta(3-) < edta(4-).

Full text of DOI:10.1039/DT9910002729

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