Reactions of triethylenetetramine with protons and bivalent zinc, cadmium, and lead in aqueous solution and aqueous dioxane (50% v/v)

The reactions of triethylenetetramine with protons and with bivalent Zn, Cd, and Pb have been studied in aqueous solution and in 50% (v/v) aqueous 1,4-dioxane, 25 °C, I = 0.10 M KNO 3 . log K (potentiometric) and ΔH (calorimetric) data are interpreted in terms of electrostatic effects and solvation effects operative in the two solvents.Protonation constants are higher by 0.2–0.6 log units in aqueous solution. Stepwise enthalpies of protonation −ΔH n (n = 2,3,4) are significantly higher, and the corresponding entropies lower, in aqueous solution. The complexes [ML] 2+ are of similar stability in the two solvents but −ΔH is ca. 10–20% lower in aqueous dioxane.