Copper(II) complexation by 6-(alkylamino)methyl-2-hydroxymethylpyridines with varying alkyl chain length in aqueous solutions. Kinetics and thermodynamics

Abstract

Kinetic parameters have been obtained from stopped-flow experiments for the complexation of copper(II) by a series of 6-(alkylamino)methyl-2-hydroxymethylpyridines with alkyl chains varying from C₁ to C₁₄, in aqueous solutions (T= 25 °C, pH 2.0–5.0). The apparent rate constants for complex formation at pH 3.5 were found to be weakly dependent on the alkyl chain length. A kinetic model has been proposed which is in excellent agreement with the experimental data, especially the change of the reciprocal relaxation time (or observed rate constant) with pH. Even in a fairly acidic pH range, the contribution of the unprotonated ligand species cannot be neglected. Equilibrium measurements were carried out in parallel using UV–visible spectrophotometry and potentiometric titrations in order to determine the values of thermodynamic parameters such as ionization and stability constants.