Abstract
The synthesis of [N,N'-bis(acetic)-N,N' bis(acetanilide)]ethylenediamine (EDDADA) and its characterisation by 1H and 13C NMR, IR and elemental analysis are reported. The interaction of this ligand with metal cations (Cu2+, Co2+, Ni2+, Cd2+, Hg2+ and Pb2+) in butan-1-ol was investigated spectrophotometrically and the stoichiometry (1:1) of the complexes was derived. Potentiometric titration curves of eddada with hydrochloric acid in water at 298.15 K show two inflection points corresponding to the protonation of the amino nitrogens of the ligand. The derived dissociation constants (expressed as pKa values) are much lower than corresponding data for EDTA. These results are in agreement with the dramatic decrease previously observed for EDTA derivatives containing acid carbonyl groups attached to the nitrogen donor atoms through a methylene spacer. Stability constants of eddada and metal cations (Cu2+, Co2+, Ni2+, Zn2+, Cd2+, Hg2+ and Pb2+) in water at 298.15 K were determined potentiometrically. These data were used to calculate the selectivity increase of mercury relative to other cations in water. Based on stability constant data, six metal-ion complexes were isolated and characterized by microanalysis and infrared spectroscopy. Thermodynamic data for the complexation of eddada with metal cations in N,N-dimethylformamide at 298.15 K show poor selective properties of this ligand for metal cations in this solvent. In fact, the similar Gibbs energies calculated are the result of an enthalpy-entropy compensation effect. Extraction experiments in the water-butan-1-ol solvent system show that eddada extracts selectively metal cations from the aqueous solution to the organic phase. The most efficient behavior for metal-ion extraction by this ligand occurs at approximately pH 4. Attempts to introduce eddada into a polymeric framework were successful. It is concluded that the new polymeric material behaves not only as an extracting agent, but also as an ion exchanger. This is confirmed by the presence of sodium ions in the aqueous solution at equilibrium. The polymeric material is easily recycled. Suggestions for further work in this area are given.