Interaction of calix[4]arene and aliphatic amines: A combined NMR, spectrophotometric and conductimetric investigation

Abstract

The constants related to the equilibria between calix[4]arene and aliphatic amines in acetonitrile were measured by conductimetric and spectrophotometric methods, and the structures of the salts studied by NMR spectroscopy. In concentrations about 10-4 mol L-1, free ions are at higher proportion, whereas at 10-2 mol L-1 there is an increase of ion-pairs proportion. The values of the constants found for acid-base reactions allow an evaluation of the value of pKa for calix[4]arene in acetonitrile as 16.6 pKa units. The analysis of data agrees with a proposal of exo-calix ammonium ion.