Micellar catalysis of metal-complex formation. Kinetics of the reaction between NiII and pyridine-2-azo-p-dimethylaniline (PADA) in the presence of sodium dodecylsulphate micelles; a model system for the study of metal ion reactivity at charged interfaces

Abstract

The kinetics of the reaction between Ni²⁺(aq) and the bidentate ligand pyridine-2-azo-p-dimethyl-aniline have been investigated in sodium dodecylsulphate micellar solutions. Considerable catalysis effects (up to 10³) are observed on the rate of complexation. The rate dependence on pH and micelle concentration can be quantitatively explained, the former in terms of the surface potential of the micelle. The reaction occurs in the region of the micelle surface, over the detergent concentration range studied, and rate constants appropriate to a surface reaction are derived. The catalysis effect resides in the concentrative effect of the micelle surface on the reagents, since the rate of water loss from Ni²⁺ at the surface of the micelle is little changed from that in bulk water. The effect of added electrolyte on the micelle-catalysed rate has also been investigated.