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

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 ex tracted species was only Ni(pan)(2) under the highly stirred system. T he extraction rate of Ni(pan)(2) was proportional to both concentratio ns 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 r ate 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(ll) complexes was explained by the ring-closure m echanism in the coordination of Hpan.