Polarographic. Study of the Reaction of Ethylenediaminetetraacetate Ion with Metal Ions in N, N-Dimethylformamide

Ethylenediaminetetraacetic acid (H4 edta) has been widely used as a chelating reagent because of its excellent complexing ability with many metal ions. In aqueous solutions, however, its chelates of the alkali metal ions are not sufficiently stable as to be applicable to analytical purpose. In this paper, the reaction of edta4- [(Et4 N)4 (edta) or (Bu4 N)4 (edta)] with Li+, Na+, K+, Rb+, Cs+, Mg2+, Zn2+ and Pb2+ ions in N, N-dimethylf ormamide has been stu died by using the polarographic method. When edta4- was added to the solution of alkali metal ions (Mt), they were precipitated as slightly soluble salts, whose compositions were M4 (edta)as determined by the amperometric technique. When the mole ratio of edta4-/M+ became larger than 1/4, the precipitates were dissolved again, and in the cases of Rb+ and, Cs+ ions, two reduction waves were observed at potentials more negative than the original waves. The limiting current of the first wave of the two waves increased with the increase of the mole ratio of edta4-/M+ and then decreased: this is attributed to the reduction of M3 (edta) and M2 ( edta) 2- ions formed in the course of dissolution of M4(edta). The limiting current of the second wave of the two waves, on the other hand, increased with the increase of the mole ratio of edta4-/M+ and reached a constant value at edta4-/M+=1/1. These facts show that RV and Cs+ ions form 1: 1 chelates or compounds with edta4-. In the cases of Li+, Na+and K+ ions, no reduction wave of 1: 1 compounds appeared. As for the bivalent metal ions (M2+), the precipitates M2 (edta) were formed by the addition of edta4-. They were dissol ved again with the increase of edta4-, and the reduction wave due to 1: 1 chelates with edta4-was observed in the case of Pb2+ ion.