EXTRACTION EQUILIBRIA OF NICKEL(II) WITH SEVERAL HETEROCYCLIC SUBSTITUTED-HYDRAZONES

The extraction of nickel(II) with seven N,N,N-tridentate heterocyclic hydrazones, a neutral form of which is abbreviated as HL, using chloro form or benzene as an extraction solvent has been studied, the extract ion equilibria being analyzed on the basis of the data for the proton dissociation of H3L2+, the formation of Ni(HL)2+ and Ni(HL)22+ complex es and the proton dissociation of Ni (HL)22+ complexes in aqueous solu tion. Nickel(II) is extracted as NiL2, although it forms such complexi ng ions as Ni(HL)2+ or Ni(HL)22+ in the aqueous phase. The distributio n constants of HL and NiL2 (the abbreviations of which are K(d) and K( dm), respectively) have been determined under the same condition as in aqueous solution. The logarithmic plots of K(dm) vs. K(d) displayed t wo straight lines with slopes of 1.9; one is for hydrazones bearing on e pyridyl or one quinolyl ring in the aldehyde moiety and the other fo r hydrazones bearing another pyridyl ring introduced to the aldehyde m oiety. This is attributed to an intramolecular hydrogen bond between t he imino hydrogen and the nitrogen of pyridine of the latter hydrazone s,