Kinetics and equilibrium of the complexation of Al 3+ with poly(maleic, acrylic) acid

Autor: W. Knoche, H. D. Narres, M. J. Schwuger, C. Fenn-Barrabaß, A. Pohlmeier
Rok vydání: 1998
Předmět:
Zdroj: Colloid & Polymer Science. 276:627-637
ISSN: 1435-1536
0303-402X
DOI: 10.1007/s003960050290
Popis: Kinetics and equilibrium of the complexation of Al3+ with a polycarboxylic acid (PCA, random copolymer of maleic and acrylic acid with a mean molecular weight of 92 kDa) are investigated by the stopped flow technique and potentiometric titration. The complexation proceeds according to the Eigen–Tamm mechanism, i.e. in first diffusion-controlled step an outer sphere complex is formed. The second rate determining step is the formation of the inner sphere complex, controlled by the exchange rate of hydration water. For this second step the rate constant is k 1=3 s-1. It is in the order of magnitude of the water exchange at the Al3+ ion as expected for the Eigen–Tamm mechanism. The activation parameters are also determined. Parallel to this direct reaction path a base catalyzed path is found, typical for complexation reactions of hydrolyzable metal ions. Stable complexes are formed for which the overall association constant K ass=Q o(1+K i) is determined by two parts: a chemical (intrinsic) part, described by the inner sphere association constant K i=3 and an electrostatically controlled part described by the outer-sphere association quotient Q o. The evaluation of the kinetic experiments allows to determine the value of log(Q o) as a function of pH: 3.3
Databáze: OpenAIRE
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