Synthesis and Alkali Metal Picrate Extraction Studies of p-tert-Butylcalix[4]arene Crown Ethers Bridged at the Lower Rim with Pyridyl Units

The syntheses of pyridyl containing calix[4]arene receptors (4, 5, and 11) that adopt the cone conformation are reported. The complexation properties of these host molecules were estimated via the results of alkali metal picrate extraction experiments. A singly-bridged bis-calix[4]arene, i.e. 4 does not appear to be an efficient alkali metal picrate extractant. A doubly-bridged bis-calix[4]arene, i.e. 5, displays elevated extraction avidity toward Rb+ and Cs+ picrates when compared with that of 4. A pyridyl containing calix[4]arene-crown-5, i.e. 11, shows improved avidity and selectivity toward extraction of K+ and Rb+ picrates vis-a-vis the corresponding behavior of 4 and 5.