EXTRACTION OF MN(II) FROM NITRIC-ACID BY CROWN ETHER-SYNERGIZED CATION-EXCHANGE - EXTENDED EQUILIBRIUM AND INFRARED-ANALYSIS

By use of the modeling program SXLSQA, it has been possible to perform an extensive equilibrium analysis of the extraction of Mn(II) from nitric acid by didodecylnaphthalene sulfonic acid (HDDNS) in combination with either t-butylbenzo-15-crown-5 (tBB15C5) or t-butylcyclohexano-15-crown-5 (tBC15C5) in toluene. Overall, only 1:1 metal:crown ether interactions have been found, and HDDNS acts both as a cation exchanger and as a solvating agent leading to small aggregates. Used alone, HDDNS exists in the form of the fourfold aggregate (HA)4 in equilibrium with the monomer HA (HA represents HDDNS with its acidic proton; associated water is omitted) and extracts Mn(II) to form the species MnH2A4. The crown ethers used alone extract Mn(II) weakly. When combined with HDDNS, tBB15C5 depresses the extraction of the metal compared with HDDNS used alone. In this case, the apparent antagonism is attributed to the interaction of HDDNS with tBB15C5 to give the adducts (HA)B and (HA)2B (B represents the crown ether). No complex of Mn(II) with tBB15C5 and HDDNS was found. However, tBC15C5 synergizes the extraction of Mn(II) by HDDNS with formation of a family of 1:1 metal:crown ether complexes of the form MnBH(a-2)A(a) (a = 2 to 4). Opposing the synergistic effect was the solvation of the crown ether by HDDNS to give a family of species of the form (HA)(a)'B (a' = 1, 2, and 4). In the analysis, activity effects in both aqueous and organic phases have been taken into account. Infrared spectra of the extraction complex MnBA2 (B = tBC15C5) in CCl4 were compared with infrared spectra of the crystalline model complex [Mn(C15C5)(DtBNS)(H2O)](DtBNS).C7H8 (where C15C5 = cyclohexano-15-crown-5 and DtBNS = 3,7-di-t-butylnaphthalene-1-sulfonate), whose structure was known from X-ray diffraction. The spectral results indicate encirclement of the extracted Mn2+ ion by tBC15C5 in solution, and sulfonate anions probably compete weakly with water for the axial coordination sites.