Kinetics and thermodynamics of complex formation between aluminium(III) and citric acid in aqueous solution

By stopped-flow and pressure-jump relaxation measurements, equilibrium and rate constants for the formation of aluminium citrate complexes have been determined at 293.7 K. For the monodentate complex, AlH2Cit2+, the bidentate complex, AlHCit+, and the tridentate complex, AlCit, the stability constants are (8.2 ± 1.5)× 102, (3.6 ± 1.6)× 106 and (5.3 ± 2.3)× 1010 dm3 mol–1, respectively. The rate constants for the formation of the monodentate and the bidentate complexes are (5.4 ± 0.5)× 103 and 80 ± 10 dm3 mol–1 s–1, respectively.