Complexation of copper(II) with 2,6-bis(dimethylaminomethyl)-4-methylphenol in the presence of surfactants

Complexation of copper(II) with 2,6-bis(dimethylaminomethyl)-4-methylphenol (HA) in water-alcohol solutions (40 vol % isopropanol) and in solutions of surfactants of different types is studied by potentiometric titration, spectrophotometry, and mathematical modeling of the equilibria. In the media studied (pH 5.5–10.5), nine copper(II) complexes with neutral and deprotonated ligands are found, that is, eight mononuclear complexes and one tetranuclear complex. The addition of surfactant affects both the composition and the stability of formed copper(II) complexes, although an unambiguous dependence of the composition of complex on the medium nature is not revealed. At equal and relatively low concentrations of complexing agent ( C_Cu2 + = 0.6 mM) and ligand (C HA = 1.6 mM), the formation of [Cu4A2]6+ complex is promoted by a nonionic surfactant Triton X-100 (TX) and a cationic surfactant cetyltrimethylammonium bromide. In water-alcohol solutions, this complex is formed at higher concentrations of reagents, i.e., at 1.94 and 5 mM, respectively. The [Cu(HA)2]2+ complex, which occurs in all of the four media studied, is the most stable in solutions of an anionic surfactant sodium dodecyl sulfate. In alkaline medium (pH ≈ 9–10), when concentration conditions are identical (C HA = 1.6 mM, C_Cu2 + = 0.58 mM), redox interactions take place only in the presence of a cationic surfactant (C CTAB = 0.5 and 5 mM) to form the copper(I) oxide precipitate. In solutions of nonionic surfactant, the precipitate is formed at higher concentrations of complexing agent ( C_Cu2 + = 1.9 mM) and ligand (C HA = 5 mM). When stored in air, copper(I) oxide precipitate is dissolved in mother liquor.