New pyridinecarboxamides for rapid extraction of palladium from acidic chloride media

The extraction of palladium(II) from hydrochloric acid solutions of various concentrations in the presence of different amounts of sodium chloride with various defined alkylpyridinecarboxamides having one or two alkyl groups in the amide substituents at positions 2, 3 or 4 was studied. The hydrophobicity of the studied reagents was characterized by various parameters, including octanol/water distribution coefficient. It was found that the extraction of palladium(II) with monoalkylpyridinecarboxamides depends upon the number, length and position of the alkylamide group. Higher extractions are observed for the derivatives with the alkylamide group at position 3. The extraction of palladium(II) from aqueous 0.1 M HCl with N-dodecylpyridine-3-carboxamide (3-C12) is rapid and the equilibrium is achieved in 30–60 s. The replacement of HCl with NaCl has only a minor effect on the extraction of palladium(II). During the extraction of palladium(II) from acidic solutions, HCl is also transferred to the organic phase. High transfer of HCl is observed for N-dodecylpyridine-3-carboxamide. A spontaneous transfer of palladium(II) to the organic phase is observed. The Vosburgh and Cooper method and the Job method were used to determine the composition of the complexes formed. Complexes with the molar ratio of palladium(II) to the extractant equal to 1:2 (PdCl2L2) and 1:1 (Pd2Cl4L2) are extracted.