Behaviour of the copper chelate of ethylenediamine tetra-acetic acid

Abstract

The copper chelate of ethylenediamine tetra-acetic acid is studied polarographically, potentiometrically and spectrophotometrically over the pH range 3-5-1 3.5 in various high concentrations of sulphate. A marked change in the polarographic reduction of the chelate is observed in strongly alkaline solutions and this is shown to be associated with an acidic ionization, CuY2-+ OH-+ Cu(OH)Y3-, in which it is suggested that the co-ordination number of copper increases from 4 to 5. The significance of observed changes in the polarographic reduction of the chelate is discussed.The copper chelate of ethylenediamine tetra-acetic acid (EDTA) is stable over a very wide pH range (above pH 2.5) and, having a high stability constant (PK 18.4), provides a suitable form in which to determine EDTA, particularly in the presence of other metallic ions. The polarographic reduction of Cu2+ to Cu in aqueous solutions of EDTA has been studied by Pecsok,l who has suggested various electrode reactions for the reduction at different pH values. A polarographic method for the determination of EDTA as its copper chelate has been described by Furness, Crawshaw and Davies,2 the method requiring the removal of excess cupric ions.

Kinetics and mechanisms of the cleavage of the chromium-carbon bond in (ethylenediamine-N,N,N',N',-tetraacetato)(hydroxyalkyl)chromium(III) complexes

“…[Crn(EDTA)(H20)]2" + -OH + H+ [Crni(EDTA)(H20)]" + H20 (12) [Cr(EDTA)(H20)]-/2-+ -OH [Cr(EDTA•)(H20)]+ H20 (13) of reaction 2 has been determined to be 5 X 10s-2 X 109 M"1 s"1.16 Therefore, the contribution of the reactions 10 and 11 to the reaction 2 may be small under the present experimental conditions because the concentrations of the alcohols are 1000-10000 times higher than [H2O2]0 and 3-30 times higher than [EDTA]0. The rate constant of the oxidation of [Cr-(H20)6]2+ by • radicals is known to be 1.2 X 1010 M"1 s"1.18 Therefore, the fc12 value may be estimated to be ~1010 M"1 s-1.…”

Ligand substitution of (ethylenediaminediacetate)vanadium(V) or (ethylenediaminetetraacetate)vanadium(V) with nitrilotriacetate ions

“…We can define new experimental values C'for each studied pH (eq 12). C'is a linear function C = C0?, + ft[H+])(l + (K0 + A:oh)[H+]) (12) of [H+] (Figure 1) with 0 ^ = 9.7 X 109 mol"2 dm6 and + 02ß2 = 7.55 X 1013 mol'3 dm9.…”