Diphenylpyrrole-Strapped Calix[4]pyrrole Extractant for the Fluoride and Chloride Anions

Abstract

The anion binding features of diphenylpyrrole-strapped calix[4]pyrrole 1 have been investigated by means of 1H NMR spectroscopy and ITC (isothermal titration calorimetry), as well as single crystal X-ray diffraction analyses. Receptor 1 bearing an auxiliary pyrrolic NH donor and solubilizing phenyl groups on the strap was found to bind F-, Cl-, and Br- as their tetrabutylammonium salts with high affinity in DMSO-d6. In addition, receptor 1 was found to extract the fluoride anion (as both its tetraethylammonium (TEA+) and tetrabutylammonium (TBA+) salts), as well as the chloride anion into chloroform-d from an aqueous source phase. Cation metathesis using TBAI or the use of a dual host approach involving crown ethers enabled receptor 1 to extract simple alkali metal fluoride or chloride salts from water. Quantitative binding of NaF by receptor 1 was observed in 20 % D2O-DMSO-d6 allowing for the direct determination of the NaF concentration in an unknown sample. Extractants: The diphenylpyrrole-strapped calix[4]pyrrole and its dual host systems involving crown ethers enable the extraction of various fluoride and chloride salts from water.image