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 pol yammonium cations (di, tri and tetra) were determined by potentiometric mea surements (H+-glass electrode), at T = 25 degrees C. To this end the proton ation 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 d ifferent amines (some of which are N-alkyl substituted) were chosen in orde r to consider several factors affecting the values of protonation constants , the chloride complex formation constants and the dependence on ionic stre ngth 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 rela tionships are reported involving chloride formation constants, parameters f or the dependence on ionic strength of protonation constants and charges in polyammonium cations. The complexes formed by two linear polyamines with N O3- have also been studied for comparison. Literature data are examined. (C ) 2000 Elsevier Science B.V. All rights reserved.