COMPREHENSIVE EQUILIBRIUM-ANALYSIS OF THE COMPLEXATION OF CU(II) BY TETRATHIA-14-CROWN-4 IN A SYNERGISTIC EXTRACTION SYSTEM EMPLOYING DIDODECYLNAPHTHALENE SULFONIC-ACID

Liquid-liquid extraction experiments, UV/vis spectra, and equilibrium modeling by use of the program SXLSQA have been employed to reveal the origin of synergism in the extraction of CU(ll) from sulfuric acid by the tetradentate macrocycle tetrathia-14-crown-4 (TT14C4) combined wi th the cation exchanger didodecylnaphthalene sulfonic acid (HDDNS) in toluene. The key feature of the system is the 1.1 complexation of Cu(l l) by TT14C4. HDDNS functions both as a source of exchangeable protons and as a solvating agent that promotes the formation of small, hydrat ed aggregates. In the absence of the cation-exchange vehicle provided by HDDNS, the macrocycle does not extract Cu(ll) detectably. Combined with HDDNS, however, TT14C4 significantly enhances the extraction of t he metal by HDDNS. Comparative UV/vis spectrophotometry indicates the formation of the deep-blue chromophore attributed to the complex ion C u(TT14C4)(2+), wherein the planar set of four endo sulfur donor atoms of TT14C4 circumscribes the metal cation. Modeling of the extraction a nd spectral absorbance data by use of the program SXLSQA supports the conclusion that this 1.1 complex accounts for essentially ail of the e xtracted Cu(ll) in excess of that extracted by HDDNS alone. The best m odel includes HDDNS aggregates incorporating Cu(TT14C4)(2+)) or Cu2+ i ons. In the analysis, activity effects in both aqueous and organic pha ses have been taken into account by the Fitter and Hildebrand-Scott tr eatments, respectively, with explicit inclusion of the formation of aq ueous hydrogen sulfate ion. The model accounts for the effect of varia tion of the solute components CuSO4, H2SO4, HDDNS, and TT14C4.