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 degreesC by potentiometric measurements. For the dependence on ionic strength of protonation constants two approaches were used: a Debye-Huckel 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) less than or equal to 1, and the relative formation constants are reported.