Potentiometric Studies on the Complexation Reactions of N-(2,2-[1-(3-Aminophenyl)ethylidene]hydrazino-2-oxoethyl)benzamide with Ni~(2+), Cu~(2+), and Cd~(2+) Ions in Aqueous Dioxane and Micellar Media

摘要

N-(2,2-[1-(3-Aminophenyl)ethylidene] hydrazino-2-oxoethyl)benzamide, aehb, was prepared by condensation of N-benzoyl glycine hydrazide with 3-aminoacetophenone and characterized on the basis of elemental and spectral data. Potentiometric studies of the Ni(II), Cu(II), and Cd(II) complexes of aehb were carried out at a constant ionic strength (I, mol · dm~(-3) = 0.10 M KNO3) at different temperatures, T = (290, 300, and 310) K, in aqueous dioxane (40 %) and in nonionic and anionic micellar media. The ligand accepted one proton in the pH range of 5.0 to 11.0 and reacted with the Ni~(2+), Cu~(2+), and Cd~(2+) ions in all media to form only 1:1 metal—ligand complexes. The protonation constant of aehb and the stability constants of the complexes had been evaluated from the pH metric titration curves employing Irving and Rossotti's pH metric titration technique. The stability constant of the complexes was in the following order: Cu(II) > Ni(II) > Cd(II). Thermodynamic parameters associated with the protonation and complexation reactions of aehb were also calculated. The values of ΔG and ΔH were negative for all of the systems in all of the media, which suggested that all of the reactions were exothermic and enthalpy-driven. The presence of surfactants in the media resulted in a decrease of the protonation constant of the ligand and stability constants of the complexes due to the compartmentalizing action of the micelles on the reacting species, and the values in different media followed this trend: aqueous > Triton X-100 (Tx-100) > Labs.