Micellar Effect on Electron Transfer Reaction of 2-(hydroxyethyl)ethylenediaminetriacetatoiron(III) Complex with Thiocarbonate Ion: Kinetic Model

Abstract

2-(Hydroxyethyl)ethylenediaminetriacetatoiron(III) ion reduction with thiocarbonate (CO₂S²⁻) in the presence and absence of sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) micelles at 33 ± 1 °C, µ = 0.1 C² M and maximum absorption = 490 nm has been investigated spectrophotometrically. The redox reaction follows pseudo-first-order kinetics which resulted to first order with respect to concentration of the both redox species with a correlation coefficient R² = 0.944 and R² = 0.9753, respectively for the complex and thiocarbonate ion. The rate of reaction accelerated and decelerated with a change in salt concentration (KNO₃) and solvent polarity (water/acetone mixture), respectively. The reaction is catalysed and inhibited by the positive electrostatic charged (CTAB) and the negative electrostatic charged (SDS) surfactants, respectively. Catalysis results are explained following the hydrophobic and electrostatic interactions between micelle aggregates and redox species, the binding constant of the complex and the thiocarbonate ion of the two micelles, and the Berezin procedure. Approximately 1.935 M⁻¹ s⁻¹, 0.9686 M⁻¹ s⁻¹, 54.619 M⁻¹ s⁻¹ and a total of 0.00 M⁻¹ s⁻¹ are obtained for the complex/CTAB, thiocarbonate ion/CTAB, complex/SDS and binding thiocarbonate ion/SDS constants, respectively. The micellar effect on this bimolecular reaction is treated in a way similar to the enzymatic catalysis where in the model assumes association of the reactants (S) to the micellar molecular (Q) as shown below;