Molecular design and synthesis of a calix[6]crown-based lithium-selective ionophore

Several 1,4-bridged calix[6]arene tetraesters were prepared from 1,4-p-tert-calix[6]crown-4’s by etherifying with ethyl bromoacetate. It was found that the 1,4-p-tert-calix[6]crown-4 tetraethylester (3a) and the 1,4-p-tert-calix[6]benzocrown-4 tetramethylester (4b) exhibit very high selectivity toward lithium and sodium ions, respectively. The ion selectivity is very sensitive to the structure of polyoxyethylene spacer and the R in the ester moiety.