Influence of the distance between ionizable groups on the protonation behavior of various hexaamines

A synthesis route for N,N,N',N'-tetraaminoethyl-1,2-ethylenediamine, N,N,N' ,N'-tetraaminopropyl-1,2-ethylenediamine, N,N,N',N'-tetraaminopropyl-1,3-pr opylenediamine and N,N,N',N'-tetraaminopropyl-1,4-butylenediamine is presen ted. These molecules differ from each other in the number of carbon atoms b etween the six amino groups. This results in different protonation behavior . Potentiometric titrations are performed in 0.1 M and 1.0 M KCl, and the s ix macroscopic protonation constants are obtained from these curves. An Isi ng model with a limited number of microscopic protonation constants and sho rt-ranged pair interactions describes the protonation behavior quantitative ly. The results are compared to those of other, similar molecules. The adva ntage of the Ising model over empirical relations such as the Taft equation s is the more systematic approach with which the titration curves of more c omplex molecules can be described. The values for the Ising model parameter s obtained here can be used to predict the protonation behavior of more com plex, in particular larger, polyamines.