Synthesis and extracting abilities of calix [4]resorcinarene-based Schiff base derivatives

Two noval calix[4]resorcinarene-based Schiff bases, 4a and 4b, which contain eight or twelve long salicylideneimine chains were easily synthesized by treating the corresponding calix[4]resorcinarenes bearing amine chains with different lengths, 3a and 3b, and salicylaldehyde in alcohol. These two amides, 3a and 3b, were obtained in a high yield by treating activated ethoxycarbonylmethoxy substituted derivatives 2a and 2b with excess 1, 6-hexanediamine. All the organic compounds were characterized by IR and H-1 NMR spectroscopy. It was found that the functional salicylideneimine arms appended to the peripheries of calix[4]resorcinarenes can fine-adjust the size and shape of the cavity upon complexation with metal ions, which significantly enhances the cation extractability.