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 NaClO 4 . 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 Fe 3+ and Fe(OH) 2+ react with the enol tautomer of the ligand. 2,4‐Octanedione reacts with Fe 3+ and Fe(OH) 2+ with rate constants of 0.65 dm 3 mol −1 s −1 , and 14.07 dm 3 mol −1 s −1 , respectively. For 2,4‐nonanedione complexation the rate constants determined are 0.49 dm 3 mol −1 s −1 , and 11.39 dm 3 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.