Extraction Equilibria of Nickel(II) with Several Heterocyclic Substituted-Hydrazones

Abstract

The extraction of nickel(II) with seven N, N, N-tridentate heterocyclic hydrazones, a neutral form of which is abbreviated as HL, using chloroform or benzene as an extraction solvent has been studied, the extraction 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⁺ complexes and the proton dissociation of Ni(HL)₂²⁺ complexes in aqueous solution. Nickel(II) is extracted as NiL₂, although it forms such complexing ions as Ni(HL)²⁺ or Ni(HL)₂²⁺ in the aqueous phase. The distribution 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 two straight lines with slopes of 1.9; one is for hydrazones bearing one pyridyl or one quinolyl ring in the aldehyde moiety and the other for hydrazones bearing another pyridyl ring introduced to the aldehyde moiety. This is attributed to an intramolecular hydrogen bond between the imino hydrogen and the nitrogen of pyridine of the latter hydrazones.