Dependence on Ionic Strength of Polyamine Protonation in NaCl Aqueous Solution

The protonation constants of several N -alkyl-substituted and unsubstituted polyamines (eight diamines, eight triamines, and four tetraamines) were determined at different ionic strengths in NaCl aqueous solutions and at 25 °C by potentiometric measurements. For the dependence on ionic strength of protonation constants two approaches were used: a Debye−Hückel type equation and Pitzer equations. The empirical parameters calculated for the two models are very similar for the same class of amines, that is, N -alkyl-substituted, partially substituted, and unsubstituted. Therefore, some general parameters and relationships that have quite good predictive value were obtained. A number of literature protonation constants were also examined in NaClO 4 at different ionic strengths using the same procedure and gave results similar to those obtained in this work. The general tertiary > secondary > primary amino group trend was observed for the dependence on ionic strength of protonation constants. The formation of polyammonium cation−Cl - ion pairs was considered in the range 0 < I /mol L -1 ≤ 1, and the relative formation constants are reported.