Kinetic and Mechanism of Oxidation of Ethylenediaminetetraacetic Acid by Alkaline Hexacyanoferrate(III)

Department of Chemistry, University of Lucknow, Lucknow-226 007

Department of Phatmacokinetic Division, Central Drug Research Institute, Lucknow

Manuscript received 23 May 1994, accepted 5 July 1994

The kinetics of oxidation of ethylenediaminetetraacetic acid (EDTA) by hexacyanoferrate(m) have been studied spectrophotometrically (λ = 420 nm) at pll = 11.0, I = 0.5 mol dm^-3 (NaCIO₄) and temperature 45°. The examination of rate data shows that the rate law is d[Fe(CN) ]/dr = k_f [Fe(CN)] [EDTA^4- with a second order rate constant k_I = 4.5 x 10^-2 dm³ mol-^I s-^I. The rate of reaction has been followed as a function of pH in the range 7.5-12.0. The rate is found to increase. The reactive species of EDTA are H₂L^2-, HL^3- and L^4-. The resolved rate constants due to the reaction of [Fe(CN)₆]^3- with EDTA^4-, HEDTA ^3- and H₂EDTA^2- are calcu­lated. The effect of ionic strength is found to be positive. The activation parameters are also calculated from Arrhenius plots. An electron transfer mechanism is suggested for the reaction.