Abstract
Three new hydrazones, in which the hydrogen at the 5-position of the pyridine ring in the hydrazine moiety of 2- pyridinecarbaldehyde 2-pyridylhydrazone was substituted by a methyl, chloro or nitro group, have been synthesized and their chromogenic properties, reactivities with metal ions and extractabilities of the metal complexes studied. The acid dissociation constants (ka) of the synthesized hydrazones were determined spectrophotometrically. These values obeyed Hammett′s law, the inductive effect of the substituents being found to reflect the pka values. Of the synthesized hydrazones, 2-pyridinecarbaldehyde 2-(5-nitro)pyridylhydrazone (PANPH), in which a electron-withdrawing nitro group was introduced, was most sensitive for metal ions. Its copper and nickel complexes showed molar absorptivities of the order of 105. A highly sensitive and selective extraction-spectrophotometric method for the determination of nickel with PANPH is proposed and has been successfully applied to the determination of nickel in steel samples. The method has been further sensitized by employing analogue derivative spectrophotometry.
