THERMODYNAMIC STUDIES OF ALKALINE-EARTH-METAL CATION COMPLEXATION BY LIPOPHILIC DIOXA, TRIOXA, AND DITHIA DICARBOXYLIC-ACIDS

Five new lipophilic dicarboxylic acids with systematic structural vari ation in the bridge which joins the two lipophilic carboxylic acid uni ts have been synthesized. Potentiometric equilibrium measurements of h ydrogen ion concentrations have been employed to determine the protona tion constants for these lipophilic di-ionizable acyclic ligands in 90 % methanol-10% water (v/v) at 25.0 degrees C and an ionic strength of 0.10 M and the stability constants for their complexes with Mg2+, Ca2 and Sr2+. Although all five ligands exhibit the highest stability con stants for Ca2+ the magnitude of the differences between the stability constants for complexation of Ca2+ versus Mg2+ or Sr2+ is found to va ry widely depending upon the identity of the bridging unit which joins the two carboxylic acid end groups.