Further relaxation kinetic investigations of iron(III) chelation. Data for diglycolic, tartaric, and citric acids

The kinetics of the reactions of iron(III) with diglycolic, tartaric, and citric acids have been studied in aqueous acid solutions by the temperature‐jump method at 25.0°C and at ionic strengths 1.0 (for tartaric and citric acids) and 0.50 mol/dm3 (for diglycolic acid). The experimental data indicate that iron(III) monochelate formation occurs by the same reaction mechanism for all three ligands examined and that only pathways involving the FeOH2+ ion contribute to the chelation process. The reacting species for citric acid is the undissociated ligand. For tartaric and diglycolic acids both the neutral ligands and the corresponding monoanions react significantly under the experimental conditions used. Kinetic evidence for the contribution of intermediate steps to the limiting rate in the overall chelate‐formation process has been obtained and discussed.