Complexation rate of vanadium(V) with 1-(2-pyridylazo)-2-naphthol solubilized on the surface of positively charged micelle

The kinetics has been investigated for the complexation reaction between vanadium(V) and 1-(2-pyridylazo)-2-naphthol in the presence of charged micelle by means of stopped-flow method. The complexation rate depends on the concentration of the surfactant in solutions containing micelle ion formed from tetradecyl dimethyl benzyl ammonium chloride. The complexation of vanadium(V) with PAN proceeds through the following two pathways; PAN + V(V) → V(V)(PAN) and (PAN)sub(s) + V(V) → V(V)(PAN). From the solubilization curve of PAN, it was shown that PAN solubilized in the tetradecyl dimethyl benzyl ammonium chloride is presumed to be existent in the neighborhood of the charged micelle surface. In addition, as the kinetic constants of complexation depend on the quaternary ammonium salt concentration, it is assumed that the chelating group of ligand is directed to the surface of micelle. Complexation rate of vanadium(V) with such ligand is affected by the hydrophilic head structure of quaternary ammonium salt, and the complexation rate at the surface of micelle formed from hexadecylpyridinium chloride is larger than the system containing tetradecyl dimethyl benzyl ammonium chloride. It is deduced that the main reactant of vanadium(V) is a neutral species, HVO3, from the observation about the pH dependence of the rate constant and the electrostatic effect of the micelle charges for the complexation rate. (auth.)