STUDIES ON POLYFUNCTIONAL O-LIGANDS - PROTONATION IN DIFFERENT IONIC MEDIA AND ALKALI AND ALKALINE-EARTH METAL-COMPLEX FORMATION OF BENZENEHEXACARBOXYLATE

The protonation of benzenehexacarboxylate [mellitate, mit (6-)] has be en studied potentiometrically, using an H+-glass electrode, in differe nt background salts: Et(4)NI (0.75), NaCl (5.0), KCI (3.0) and LiCl (1 .0) (in parenthesis the maximum value of ionic strength in mot dm(-3) is reported), at 25 degrees C. Protonation constants at different ioni c strengths were fitted by different models. Differences in protonatio n constants in different media were also interpreted in terms of compl ex formation, and stability constants fdr alkali metal complexes were calculated. The Na+-mlt complex formation has been confirmed by ISE-Na measurements. By potentiometric measurements in the presence of Mg2(pH) and Ca2+ (pH and pCa) it was possible to obatin the formation con stants for alkaline earth metal complexes. The stability of alkali and alkaline earth metal complexes is discussed in comparison with analog ous carboxylic complexes.