Mono-complex formation kinetics of iron(III) with nonsubstituted octane and nonane 2,4-dicarbonyl ligands in aqueous solution

The kinetics and mechanism of the reaction of complexation of iron(III) with 2,4-octanedione and 2,4-nonanedione have been investigated spectrophotometrically in aqueous solution at 10°C and ionic strength 0.5 mol dm^?3 NaClO₄. The equilibrium constants of the mono-complexes have been determined. The mechanism proposed to account for the kinetic data involves a double reversible pathway where both Fe³⁺ and Fe(OH)²⁺ react with the enol tautomer of the ligand. 2,4-Octanedione reacts with Fe³⁺ and Fe(OH)²⁺ with rate constants of 0.65 dm³ mol^?1 s^?1, and 14.07 dm³ mol^?1 s^?1, respectively. For 2,4-nonanedione complexation the rate constants determined are 0.49 dm³ mol^?1 s^?1, and 11.39 dm³ mol^?1 s^?1, respectively. Some discussions are made on the basis of Eigen-Wilkins theory considering the effect of solvent exchange on the complex formation. © 1993 John Wiley & Sons, Inc.