The reaction of dicarboxylic acids containing ether linkages with alkaline earth metals

Abstract

Four dicarboxylic acids (Reagents I, II, III and IV) containing ether linkages, HOOCCH 2O-(CH 2CH 2O) n CH 2COOH ( n = 0–3), were synthesized. The acid dissociation constants and their chelate stability constants with alkaline earth metals were measured by pH titration method at an ionic strength μ = 0·10 and at 25·0 ± 0·1°C. As the total sum of the number of oxygen atoms of ether linkages and carbon atoms approaches infinity, the value of the ratio of the first to the second acid dissociation constant comes near to four. Therefore, it indicates that the molecules behave statistically, when the number of atoms between two carboxyl groups approaches infinity. The decreasing order of the stability constants of those chelates with alkaline earth metals is as follows: Reagents I and II ( n = 0 and 1; Ca < Sr < Ba < Mg Reagents III ( n = 2; Ca < Sr < Ba < Mg Reagents IV ( n = 3; Sr = Ba < Ca < Mg.