Study of Equilibria in the Aluminium(III)‐Glycine and ‐Alanine Systems

The formation of various hydrolytic and mixed hydrolytic complexes of the aluminium(III) ion in the presence of glycine and L‐alanine, has been studied in 0.5 mol dm −3 (Na)NO 3 medium at 25deg;C, by emf method. The concentration ratios of amine acids to aluminium(III) were varied from 1 : 1 to 10 : 1. The least‐squares treatment of the data obtained, in the absence of the amino acids, indicates the formation of the dimer, [Al 2 (OH) 2 ] 4+ , and monomer, [AlOH] 2+ , with the stability constants log β 22 = −7.03 ± 0.03 and log β 11 = −5.65 ± 0.09, respectively. At pH values higher then ∼4.0 formation of the trimer [Al 3 (OH) 4 ] 5+ (log β 34 = −12.60 ± 0.08) becomes significant. In the presence of amino acids the evidence has been found for the formation of [Al 2 (OH) 4 ] 2+ (log β 24 = −15.65 ± 0.09). Besides the formation of the pure hydrolytic complexes, equilibria in the title systems can be explained by assuming the main reaction products to have the compositions [Al(OH) 3 Gly] (log β 131 = −7.53 ± 0.04), [Al 2 (OH) 2 (Gly) 2 ] (log β 222 = 6.56 ± 0.09) and [Al(OH) 3 Ala] (log β 131 = −7.70 ± 0.03), [Al 2 (OH) 2 Ala 2 ] (log β 222 = 7.23 ± 0.07).