Kinetic study of cobalt(II) and pyridine-2-azo-paradimethyl aniline in mixed solvents

The rate constants for the formation of the one-to-one complex of cobalt(II) and pyridine-2-azo-para-dimethylaniline were studied in water and in 4%, 7%, 10% and 30% methanol-water mixtures at 15[degrees]C, 25[degrees]C and 35[degrees]C. Formation rate constants were calculated from the relaxation data obtained by the temerature jump method. A pH range was maintained at which the ligand was electrically neutral. The rate constants and the activation parameters calculated from the rate data were interpreted in terms of Eigen's multi step mechanism for metal ion complex formation in solution. These results indicate that methanol has a considerable influence on the structure of the bulk solvent. It was concluded that in low concentrations, methanol imposes greater order in the bulk solvent up to about 4 mole percent concentration; beyond this concentration, it tends to decrease the order in the bulk solvent.