Relaxation kinetic study of iron(III) chelation with glycolic and lactic acids. Contribution of intermediate steps to the limiting rate in the overall process

The kinetics of formation of iron(III) monochelates with glycolic and lactic acids have been investigated by the temperature-jump method at 25.0°C and ionic strength 1.0 M over the acidity range 0.0200 – 0.900 M. The kinetic data indicate that two reaction paths, involving the FeOH²⁺ ion and the neutral and anionic (HL-L⁻) forms of the ligands, lead to the iron(III) chelate formation and that the monodentate complex Fe(OH)L-LH⁺ is formed as an intermediate compound. Moreover the observed [H⁺]-dependence of the forward rate constants permits us to estimate the contribution of intermediate steps to the limiting rate in the overall chelate formation process.