The dependence on ionic strength of enthalpies of protonation for polyamines in NaCl(aq)

Enthalpies of protonation of some polyamines [N ,N ,N' ,N' -tetramethylethylenediamine, bis(3-aminopropyl)-amine, bis(6-aminohexyl)amine, 4-aminomethyl-1,8-octanediamine, 3,3'-diamino-N-methyldipropylamine, N ,N ,N ',N ',N "-pentamethyldiethylenetriamine, 1,1,4,7,10,10-hexamethyltriethylenetetraamine, and tris-(2-aminoethyl)amine] were determined by calorimetric titrations in NaCl((aq)) in the ionic strength range 0 < I /(mol kg(-1)) less than or equal to 3 [0 < I/(mol kg(-1)) less than or equal to 5 for bis(6-aminohexyl)amine and tris(2-aminoethyl)amine] and at t = 25 degreesC. The dependence on ionic strength was considered by using two different models. Both DeltaH(0) values and their dependence on I are affected by N-alkyl substitution. Parameters for the dependence on I are very similar for all unsubstituted or partially substituted polyamines, and common parameters are proposed. Analogously, for fully methyl-substituted polyamines, strong similarities were found in the dependence on 1, and also in this case, common empirical parameters are given. Previous data from this laboratory for the protonation of some unsubstituted diamines were also considered in the analysis of the results. An attempt to calculate enthalpy changes for the interaction of Cl(-) with polyammonium. cations was made.