Hydration and interfacial activity of methyl 8-pyridyloctanoates and extraction of copper(II) from chloride solutions

The interfacial tension of individual methyl 8-pyridyloctanoates containing the hydrophobic group at different positions of the pyridine ring was measured at the tolune/water interface. The extraction of copper(II) fom chloride solutions with these reagents was studied. Considering solvent extraction, methyl 8-(2-pyridyl)octanoate had a worse orientation at the interface than methyl 8-(3-pyridyl)octanoate and methyl 8-(4-pyridyl)octanoate. PM3 semiempirical quantum chemical computing indicates that the oxygen of the carbonyl group forms hydrogen bonds with water molecules more easily than the second oxygen atom and the nitrogen in the pyridine ring. However, at the adsorption layer, this hydration is possible only for methyl 8-(2-pyridyl)octanoate. Methyl 8-(3-pyridyl)octanoate and methyl 8-(4-pyridyl)octanoate are strong copper extractants from chloride solutions, while extraction is not observed for methyl 8-(2-pyridyl)octanoate.