Di-ionizable p - tert -butylcalix[4]arene-1,2-crown-5 ligands in the cone conformation: effect of acidic side arm length for solvent extraction of divalent metal ions

Abstract Several new di-ionizable p - tert -butylcalix[4]arene-1,2-crown-5 compounds were prepared in the cone conformation. For comparison with reported ligands, the systematic structural variation was a change of the pendent acidic groups from two adjacent –OCH 2 CO 2 H or –OCH 2 C(O)NHSO 2 Z (with Z=–Me, –Ph, –C 6 H 4 –4-NO 2 , –CF 3 ) units to two adjacent –O(CH 2 ) 4 CO 2 H or –O(CH 2 ) 4 C(O)NHSO 2 Z groups. Competitive solvent extractions of alkaline earth metal (AEMC) cations from aqueous solutions into chloroform by these ligands were performed. Also single species solvent extractions were conducted for the divalent heavy metal cations of Pb 2+ and Hg 2+ . Comparison of the extraction data for the new ligands with those reported reveal that the ligands with shorter proton-ionizable side arms are more effective divalent metal ion extractants.