New 5,17-(di-ionizable)-25,26,27,28-tetraalkoxycalix[4]arene ligands: synthesis and selected divalent metal ion extractions

Four new series of 5,17-(di-ionizable)-25,26,26,28-tetraalkoxycalix[4]arene ligands are prepared. The ionizable groups are carboxylic acid and N-(Z)sulfonyl formamide functions with Z = –Me, –Ph, –C6H4–4-NO2, and –CF3. When the four alkoxy groups are methoxy, the ligand conformation is flexible. With four butoxy groups, the ligands are locked in cone, partial-cone, or 1,3-alternate conformations. Complexation abilities of the new ligands are evaluated in solvent extractions of selected divalent metal ions from aqueous solutions into chloroform. Both the conformation of the calix[4]arene unit and identity of the acidic group are found to influence the divalent metal ion extraction selectivity and efficiency.