Kinetic investigation of formation and dissociation of iron(III) monophenolate complexes

Abstract

The temperature-jump method has been used to investigate the kinetics of formation and dissociation of monocomplexes of iron(III) with some substituted phenols (HA) in aqueous solution at 25° and ionic strength 0·10M over the acidity range 0·010—0·090M. The only reaction observed is FeOH²⁺+ HA ⇄ FeA²⁺+ H₂O. All the estimated rate constants for the forward reaction are of the same order of magnitude as those found for other analogous reactions previously studied. This result is consistent with a mechanism in which release of a co-ordinated water molecule from the inner sphere of the cation is rate-determining. The rates for the reverse process decrease with decreasing base strength of the ligands and follow the Hammett relationship with a reaction constant ρ=–0·33.