PROTONATION OF NONCYCLIC AND CYCLIC DIAMINES IN AQUEOUS-SOLUTION

Potentiometric and calorimetric methods were used to determine the pro tonation constants and thermodynamic values of the protonation of diff erent noncyclic 1,5-diamines, noncyclic 1,8-diamines and cyclic 1,8-di amines in aqueous solution. The ligands were modified by oxygen and su lfur atoms at the 3- and 6-position. The measured values of the stabil ity constants and reaction enthalpies are compiled with data from the literature. The protonation constants of the alkyl diamines exceed tho se of the alkyl diamines containing oxygen or sulfur atoms by more tha n one order of magnitude. The main contribution to the protonation con stants of the noncyclic ligands is the reaction enthalpy. The values o f the reaction entropies of the noncyclic diamines are nearly constant and close to zero. No intramolecular stabilization of the protonated amines by hetero atoms could be observed in aqueous solution. (C) 1997 Elsevier Science B.V.