COMPLEX-FORMATION BETWEEN THE MACROCYCLIC LIGAND 18-CROWN-6 AND UNPROTONATED AMINES IN METHANOL

The complexation reactions between different amines and the macrocycli c ligand 18-crown-6 have been studied in methanol. Calorimetric titrat ions have been performed in order to obtain the stability constants an d the reaction enthalpies and entropies for these reactions. The stabi lity constants of all amines studied are within the same order of magn itude. However, alkyl and aryl substituents strongly influence the val ues of the reaction enthalpies and entropies. In contrast, for all sec ondary and tertiary amines examined nearly identical values for the re action enthalpies and entropies are observed. As a result, the number of hydrogen bonds formed between the crown ether and these amines is n ot the most important factor.