A STUDY ON APPLICATIONS OF HETEROCYCLIC H YDRAZONES IN ANALYTICAL-CHEMISTRY

Although a large number of nitrogen-heterocyclic hydrazones have been used as chromogenic reagents in the spectrophotometric determination o f divalent transition metal ions, there is only a little information o n the complexation behavior of these hydrazones in terms of thermodyna mics and kinetics. In order to increase sensitivity or solubility, bul ky substituents such as pyridyl and quinolyl groups are often introduc ed into extractive-spectrophotometric reagents. However, application o f linear free energy relationship (LFER) to formation of metal-multide ntate ligand complexes has been scarcely discussed. In this study, the extractive-spectrophotometric determination of trace metal ions and a nions with hydrazones were established. The extraction behavior was in terpreted in terms of complexation parameters in aqueous or aqueous-di oxane solution and LFER. The extraction mechanisms were confirmed by e quilibrium and kinetic experiments. First, the acid-base equilibria we re discussed in connection with the ligand structures with the aid of several spectrometric (NMR, X-ray etc.) results. Second, the formation constants of the Ni(II), Cu(II) and Fe(II) complexes with a series of hydrazones were determined. The LFER between formation and proton dis sociation constants showed several structural effects, in addition to the effect of basicity, which were caused by the N,N,N-heterocyclic st ructure. The LFER obtained were discussed in connection with thermodyn amic and ligand field parameters and were reasonably explained by the additivity of the structural effects on the formation constants. Third ly, the extraction equilibria of nickel(II) were elucidated based on t he results of the second study. The extraction kinetics was discussed in conjunction with the rate constants of formation of nickel(II)-hydr azone complexes. Finally, a method for the determination of trace elem ents with hydrazones having a di-2-pyridyl ketone moiety was proposed and some favourable effects of the ketone moiety were discussed.