Interfacial reaction in the synergistic extraction rate of Ni(II) with dithizone and 1,10-phenanthroline

The kinetic synergistic effect of 1,10-phenanthroline (phen) on the extraction rate of Ni(II) with dithizone (HDz) into chloroform was studied by means of a high-speed stirring method combined with photodiode-array spectrophotometry. The initial extraction rate of the adduct complex NiDz(2)phen depended upon the concentrations of both HDz and phen, suggesting the formation of NiDzphen(+) as the rate-controlling step. When [HDz] < [phen], the initial extraction of NiDz(2)phen competed with the formation of an intermediate complex, which was adsorbed at the interface and assigned most probably to NiDzphen(+)(2). The intermediate complex was gradually converted to NiDz(2)phen at a later stage of the extraction. The rate constants for the formation and consumption of the intermediate were determined, and the kinetic mechanism in the synergistic extraction was discussed.