Gamma radiolysis of copper (II) nitrilotriacetate in aqueous solution

Abstract

Aqueous solutions of copper (II) nitrilotriacetate (Cu^IINTA) were irradiated with ⁶⁰Co-gamma rays in deaerated conditions as well as in the presence of various scavengers such as O₂, N₂O, NO^–₃, HCOO^– and aliphatic alcohols. Both e^–_aq and H were found to reduce the metal ion directly. In the presence of scavengers such as HCOO^– the reduced complex decomposes to yield Cu₂O. The reaction of OH with the complex leads to the production of iminodiacetic acid (IDA) and the carbonyl compounds, formaldehyde and glyoxalic acid. It is argued that HCHO is formed in the system by the decomposition of transient Cu^IIINTA formed by oxidation of the metal ion by OH; CHOCOOH, on the other hand, is produced from the radical formed by hydrogen abstraction by OH from the α-carbon atom of the ligand. The rate constants for the two reactions have been evaluated by competition kinetic studies as (1.02 ± 0.06)× 10⁹ dm³ mol^–1 s^–1 and (3.3 ± 0.3)× 10⁸ dm³ mol^–1 s^–1 respectively. In the presence of the scavengers, N₂O or NO^–₃ the metal ion is ultimately reduced to Cu₂O. However, in the presence of aliphatic alcohols and in the absence of any scavenger, Cu^IINTA solutions acquired a red colour on radiolysis which was highly sensitive to oxygen. These red solutions were found to have characteristic broad absorption spectra, and these are ascribed to the presence of copper–carbon linkages. When the radiolysis was carried out in presence of oxygen neither the red coloration nor precipitation of Cu₂O was observed.