Protonation of polyamines in NaCl aqueous solution and binding of Cl- by polyammonium cations

Equilibrium constants relative to the binding of Cl- by nine open chain polyammonium cations (di, tri and tetra) were determined by potentiometric measurements (H+-glass electrode), at T = 25 degrees C. To this end the protonation constants of these amines were measured in NaCl aqueous solutions, in the ionic strength range 0.1 < I less than or equal to 1 mol dm(-3). The different amines (some of which are N-alkyl substituted) were chosen in order to consider several factors affecting the values of protonation constants, the chloride complex formation constants and the dependence on ionic strength of apparent protonation constants. As concerns these last two points, it was found that fully N-alkyl substituted amines behave in a very similar way, with respect to partially or non-substituted ones. Simple linear relationships are reported involving chloride formation constants, parameters for the dependence on ionic strength of protonation constants and charges in polyammonium cations. The complexes formed by two linear polyamines with NO3- have also been studied for comparison. Literature data are examined. (C) 2000 Elsevier Science B.V. All rights reserved.