Protolytic and Complexing Properties of N-(2-Hydroxyethyl)-Iminodipropionic Acid in Aqueous Solution

Acid dissociation constants of functional groups in N-(2-hydroxyethyl)iminodipropionic acid have been determined by alkalimetric titration in aqueous solution with pH-potentiometric indication at I = 0.1 mol/L (KCl/KNO3) and t = 25 ± 1°C: pKa0 = 2.87 ± 0.02, pKa1 = 4.00 ± 0.02, and pKa2 = 9.25 ± 0.01. Complex formation of the compound with transition metal ions has been studied. It has been shown that the presence of 2-hydroxyetyl substituent in iminodipropionic acid leads to considerable decrease of stability of complexes with copper(II) and nickel(II), whereas the stability of coordination compounds with cobalt(II), zinc(II), and cadmium(II) slightly increases. Complexes with silver(I) cations exhibit relatively high stability. Assumptions on the structure of the studied complexes has been made on the basis of the data obtained.