EQUILIBRIA AND KINETICS OF ALUMINUM(III) COMPLEX FORMATIONS WITH SEMI-XYLENOL ORANGE AND SEMI-METHYLTHYMOL BLUE

The equilibria and kinetics of complex formations by Al(III) with Semi-Xylenol Orange (SXO) and Semi-Methylthymol Blue (SMTB) in aqueous solution have been investigated potentiometrically and spectrophotometrically. Al(III) forms three complex species, AlHL, AIL- and Al(OH)L2-. The stability constants were determined and their structures have been discussed. Kinetic results are interpreted in term of a two-step mechanism including a pre-equilibrium. Second order rate constants of the forward reaction between the Al(III) aquo ion and ligand acid species were determined from the dependence of the reaction rate on the hydrogen ion concentration. Substitution of the water in the Al(III) aquo ion by the ligand species is assumed to involve several water molecules including the outer sphere water and the removal of these is assumed to be the rate determining. The rate was accelerated by the addition of a polar organic solvent. © 1979.