Rate constants and equilibria of monochelate formation of iron(III) with 2-acetylcyclohexanone

Abstract

Kinetics and equilibria in aqueous 1:1 chelation of iron(III) by 2-acetylcyclohexanone have been investigated spectrophotometrically in aqueous solution at 25°C and 0.5 mol dm-3 NaClO4. In conjunction with earlier work, the results suggest that the deprotonation rate of the keto tautomer of 2-acetylcyclohexanone has a minimum value when compared with 1,3-dicarbonylic ligands of similar structure. The mechanism proposed to account for the kinetic data involves pathways in which both Fe3+ and Fe(OH)2+ react with the enol tautomer of the ligand. The relative rates of complex formation are shown to depend not only on the metal species involved but also on ligand structure factors such as steric hindrances, ring strain and intramolecular hydrogen bonding.