Effect of the alkyl chain length in N,N-dialkylpyridine-3-carboxamides upon their extraction of copper(II) from aqueous chloride solutions

Three nicotinamide derivatives with two butyl, hexyl, or octyl alkyl chains at amide nitrogen were synthesized. These model individual compounds were used for copper(II) extraction from acidic chloride solutions at constant ionic strength I = 1.0. It was found that during the extraction N,N-dialkylpyridine-3-carboxamides form two complexes with copper(II) and chloride ions; these can transfer into the organic phase. In these complexes the molar ratio of copper: chlorine : extractant = 1 : 2 : 2 or 1 : 2: 3. The obtained stability constants of N,N-dihexyl- and N,N-dioctylpyridine-3-carboxamides complexes with copper(II) chloride in water are comparable, but N,N-dibutylpyridine-3-carboxamide complexes stability constants are significantly lower. The partition constants of these complexes in toluene-water system depend on amide hydrophobicity, increasing with increasing carbon chain length in N,N-dialkylpyridine-3-carboxamides.