Medium effects upon the kinetics of formation of nickel(II) and cobalt(II) pyridine 2-azo-p-dimethylaniline

Summary The kinetics of formation of the Ni^II and Co^II complexes of pyridine 2-azo-p-dimethylaniline have been studied in aqueous ethylene glycol, aqueous glycerol and in moderate (up to 2.5 mol dm^–3) concentrations of NaCl at 298.2K.Mole fractions of 0.24 and 0.12 respectively for ethylene glycol and glycerol effect a lowering of the formation rate constant K_f of Ni(PADA)²⁺ to about 50% of the value in water. A concentration of 2.0 mol dm^–3 NaCl doubles k_f for both the Ni and Co complexes. These findings are discussed within the framework of the dissociative interchange mechanism; the possible effects upon each step of the mechanistic pathway are considered.