ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

New complexons. XIII. Potentiometric and electrophoretic study of ethylenediamine-N,N'-disuccinic acid and its metal chelates

J. Majer, V. Jokl, E. Dvořáková, and M. Jurčová

Department of Analytical Chemistry, Faculty of Pharmacy, Komenský University, Bratislava

Abstract: The chelate-forming properties of the ethylenediamine-N'-disuccinic acid (C₁₀H₁₆O₈N₂) (EDDJ) with the aid of potentiometry and of paper electrophoresis are studied. From the Potentiometrie measurements both acidity constants and stability constants of EDDJ chelates with bivalent ions Ca, Mg, Sr, Ba, Cu, Zn, Cd, Mn, Pb, Co for the ionic strength I = 0.1 (KN0₃); t = 20 °C were derived. The assumed composition (1:1) and the charge of the named complexes has been proved by the electrophoretic mobility curves analysis. On the basis of this curves the approximative stability constants of the chelates with the above ions as well as those of chelates with Ni(II), Fe(III), Al(III), and La(III) were graphically evaluated. The stability of EDDJ metal chelates is compared with the ethylenediamine-.N,N'-diacetic-N,N'-dipropionic acid (EDDADP), which, similarly to EDDJ and in contrast to EDTA, can form three five-dentate and two six-dentate rings. The presence of secondary amino-groups in the EDDJ molecule influences the acidity constants values k_H2А and k_HA which are lower than those of EDDADP. The stability of the EDDJ chelates is — in spite of the shift k_HA — on the average lower by the unit log K_MA with the exception of Сu and Ni chelates. This lowering by log K_MA in the EDDJ is ascribed to the deformation of six-dentate rings which is due to different structure of chelates. In comparison with EDTA, a greater decrease of Cd, Pb and alkali earths complexes stability was observed. The relatively lowest depresion of the stability constant was found to be that of Ca-complex (decrease by 6 units log K_MA), SO that the stability decreases in the following order: Mg > Ca > Sr > Ba. Finally, it can be stated, that the EDDJ has certain selectivity power in comparison with EDTA.

Full paper in Portable Document Format: 226a415.pdf (in Slovak)

Chemical Papers 22 (6) 415–423 (1968)