New di-ionizable p-tert-butylcalix[4]arene-1,2-crown-4 ligands: synthesis and divalent metal ion extraction

New di-ionizable p-tert-butylcalix[4]arene-1,2-crown-4 ligands with elongated side arms in cone, partial-cone, and 1,2-alternate conformations of the calixarene scaffold are prepared and characterized. The acidic groups on the side arms include carboxylic acid and N-(X)sulfonyl carboxamide with X variation of –Me, –Ph, –C6H4–4-NO2, and –CF3. Solvent extractions of alkaline earth metal cations, Hg2+, and Pb2+ from aqueous solutions into chloroform are employed to probe the effects of these structural modifications on the divalent metal ion complexation behavior of the new ligands.