Metal extraction in micellar media: a comparison of copper complexation rates and ultrafiltration yields of two isomeric (E)-1-(2′-hydroxy-5′-alkylphenyl) 1-alkanone oximes

Abstract

Copper(II) complexing and extracting properties in micellar media of two isomeric hydroxyoximes differing in the location of their hydrophobic alkyl chain [(E)-1-(2′-hydroxy-5′-nonylphenyl)-1-ethanone oxime (1) and (E)-1-(2′-hydroxy-5′-methylphenyl)-1-decanone oxime (2)] are compared. Stopped-flow kinetic measurements were conducted in cetyltrimethylammonium bromide (CTAB) and n-dodecyl hexa(ethylene glycol) ether (C₁₂EO₆) micelles and in methanol. The rates of complexation were very similar in methanol, while complexation in micellar solutions at pH 5 was faster with 2 than with 1. The pH dependence of the observed rate constants was consistent with a Hague–Eigen type mechanism. The practical removal of copper from dilute aqueous solutions was investigated using micellar extraction coupled with ultrafiltration. Close to 100% removal was achieved with both surfactant systems at pH 6.2, with a ligand : metal ration of 5. Ligand 2 appeared to be slightly more efficient than ligand 1. The effect of pH on extraction yield was studied in more detail with 1. The results of both the micellar extraction and kinetic studies have been discussed in relation to previous experiments involving classical extraction using water/xylene biphasic systems.