SALT EFFECTS ON THE PROTONATION OF DIETHYLENETRIAMINE - A COMPLEX-FORMATION MODEL

Protonation constants of diethylenetriamine (dien) have been determined potentiometrically, using (H+)/glass electrode in different aqueous media (NaCl, KCl, NaClO4, NaI, NaNO3, MgCl2, CaCl2 and tetraethylammonium iodide) at 25-degrees-C and 0 < I less-than-or-equal-to 1 mol l-1. Measurements at very low ionic strength and in KCl (0 < I less-than-or-equal-to 1 mol l-1) were also carried out at different temperatures (10 less-than-or-equal-to T less-than-or-equal-to 40-degrees-C). The differences in lg K(j)H values are explained using a complex formation model by taking into account the formation of (dien)H(q)X(p) and M(dien)H(q) weak species (X = Cl-, ClO4-, I-, NO3-; M = Ca2+, Mg2+, tetraethylammonium cation). Formation thermodynamic parameters are given. The speciation of diethylenetriamine in mixed electrolytes is discussed in relation to the real composition of natural fluids.