Aluminum(III)-Malonate Equilibria: a Potentiometric Study

Abstract

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 AlL₃^3- (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 K_D= -6.68). The protonation constants determined for malonic acid were log K₁ = 5.43 and log K₂ = 2.60 (corrected for K⁺ ion pairing).