Synthesis, characterization and use of imidazole and methyl-pyrazole based pyridine ligands as extractants for nickel(II) and copper(II)

[Display omitted] •High Nickel(II) extraction was obtained in combination with a novel synergist.•With competitive extraction, Cu(II) has the highest extraction followed by Ni(II).•Kinetic studies shows that after at most 4 h, extraction equilibrium is established. This work consists of the synthesis of seven pyridine based ligands, 2-(3-butyl-1H-pyrazol-5-yl)-pyridine (1), 2-[3-(tert-butyl)-1H-pyrazol-5-yl]-pyridine (2), 2-(3-octyl-1H-pyrazol-5-yl)-pyridine (3), 2-(1-octyl-1H-imidazol-2-yl)pyridine (4), 2-[(1H-pyrazol-1-yl)methyl]pyridine (5), 2-[(3,5-dimethyl-1H-pyrazol-1-yl)methyl]pyridine (6) and 2-[(3-methyl-1H-pyrazol-1-yl)methyl]pyridine (7) which have been made before. We modified some routes and obtained improved yields in most cases. The ligands were fully characterised using 1H and 13C NMR, infrared (IR) spectroscopy, mass spectrometry (ms), elemental analysis (EA) and melting point where appropriate. We managed to grow single crystals of the 2-[(1H-pyrazol-1-yl)methyl]pyridine copper(II) perchlorate complex and solved the structure using single crystal X-ray diffraction. Coordination around the copper(II) centre is pseudo square planar, having two ligands coordinated to the metal ion. Indications are that the extraction stoichiometry using this ligand for copper(II) is also 2:1, L:M. This indicates how these ligands are capable of coordinating to metal ions. All the ligands were then used for the extraction of Ni(II) with and without a synergist, viz., sodium p-dodecylbenzenesulfonate (SDBS). The solvent extraction of only Ni(II) in the absence of synergist produced values from 3% to 15% and values between 69% and 79% with synergist. The competitive extraction of metal ions from a base metal ion mix (Co2+, Ni2+, Zn2+, Cu2+, Pb2+ and Cd2+) produced extraction values of 15%−87% extraction of different metal ions with synergist. Finally, time dependent extraction studies with Ni(II) showed that after 4 h equilibrium was established and in some cases even after 1 h equilibrium had been reached.