Catalytic Effect of N,N-Dimethyl-4-(2-pyridylazo)aniline on the Extraction Rate of Ni(II) with 1-(2-Pyridylazo)-2-naphthol: Ligand-Substitution Mechanism at the Liquid-Liquid Interface

摘要

The catalytic effect of N,N-dimethyl-4-(2-pyridylazo)aniline (PADA) on the extraction rate of Ni(II) with 1-(2-pyridylazo)-2-naphthol (Hpan) in toluene was investigated by the high-speed stirring method. The extracted species was only Ni(pan)_2 under the highly stirred system. The extraction rate of Ni(pan)_2 was proportional to both concentrations of Ni(pada)~(2+) adsorbed at the liquid-liquid interface and Hpan in the toluene phase, suggesting that the rate-determining step was the reaction between Ni(pada)~(2+) and Hpan at the interface, followed by a successive fast ligand-substitution reaction with another Hpan. The rate constant for the rate-determining step was estimated as 90 ± 6 M~(-1) S~(-1). That the value was rather smaller than the ordinary formation rate constants of Ni(II) complex was explained by the ring-closure mechanism in the coordination of Hpan.