Synthesis, conformational analysis and extraction studies of p-isopropylcalix[n]arene derivatives (n=4, 6, 8). A new family of molecular receptors

Ethers, esters and ketones, derivatives of p-isopropylcalix[n]arenes (n = 4, 6, 8), have been prepared; 33 new molecular receptors have been isolated and fully characterized. H-1 NMR and C-13 NMR measurements reveal that tetraester and tetraketone derivatives are in cone conformation at room temperature when hexa and octa derivatives look like flexible flattened cones. Extraction studies with metal picrates from aqueous solution into dichloromethane were used to assess the ionophoric activity of the p-isopropylcalix[n]arene derivatives. The better E% are obtained with tetrameric derivatives in cone conformation, fully functionalized on the phenolic oxygens by ester or ketonic groups. The tetraamide derivative is the most efficient binder; the E% values are around 100 for Li, Na, K, Rb, Cs, Ca and Ba.