Interaction of Calix[4]arene and Aliphatic Amines: A Combined NMR, Spectrophotometric and Conductimetric Investigation

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.