Abstract
The interaction of excess hydrolyzed aluminum(III) cation in mildly acid aqueous media with ferron (7-iodo-8-hydroxyquinoline-5-sulfonic acid) has been studied unsing stopped-flow. Three distict transients are observed. The shortest-lived, which is largest in amplitude, has been assigned to mono-complex formation. The other two transients, which are much smaller in amplitude, are interpreted as reactions of dimeric and other polymeric aluminum(III) species.
The hydrogen ion dependences of the observed rate constants for mono-complex formation indicate participation of Al(OH)+2 in the dominant pathway. Analysis of these results, using the Eigen model of complexation, leads to a water exchange rate constant of(4.0 ± 0.4) × 107 sec−1 for Al(OH)−2.
The slower transients could not be adequately explained by formation of bis and tris-complexes. Assignment of these transients to reactions of μ-hydroxy-bridged aluminum dimer with ferron, coupled to mono-complex formation leads to an adequate data fit. The polyphasic nature of the aluminum-ferron interaction over the pH range 2–5 can be understood as showing different groups of reactions, rahter than differently reacting metal-containing species.