Aluminum(III)-Malonate Equilibria: a Potentiometric Study

The aluminium(III)-malonic acid (H2L) equilibria have been studied by potentiometric titration in aqueous solution at 25°C (I = 0.10 M KCl ). Data were consistent with the formation of simple binary complexes AlL + (log K1 = 6.711), AlL2- (log K2 = 4.815) and AlL33- (logβ3 = 14.104) in the pH range 2.2-5.5. There was also evidence for a minor species AlL2(OH)2- at pH > 5.8 for solutions with [Al3+]:[LH2] < 3.0 (log KD= -6.68). The protonation constants determined for malonic acid were log K1 = 5.43 and log K2 = 2.60 (corrected for K+ ion pairing).