Reactions of co-ordinated ligands. Hydrolysis of tetramethyl ethylenediaminetetra-acetate and its copper(II) complexes
- 1 January 1975
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in J. Chem. Soc., Dalton Trans.
- No. 13,p. 1348-1351
- https://doi.org/10.1039/dt9750001348
Abstract
Tetramethyl ethylenediaminetetra-acetate, Me4edta, interacts with copper(II) ions to give the complex [Cu(Me4edta)]2+ in which probably two ester groups of the ligand are bonded to the metal ion in conjunction with the two nitrogen donors. Base hydrolysis of two ester groups occurs in the pH range 4·1–5·4 with kOH= 3·23 × 105 and 7·02 × 104 I mol–1 s–l at 25 °C and I= 0.lM. These constants apply to the hydrolysis of [Cu(Me4edta)]2+ and [Cu(Me3edta)]+, respectively. Hydrolysis by water also occurs in this pH range. Hydrolysis of the second pair of ester groups takes place in the pH range 7·2–9·0 with KOH= 1·54 × 103 and 7·47 × 10 I mol–1 s–1 at 25 °C. Base hydrolysis of the first ester groups of [Cu(Me4edta)]2+ is ca. 105 times faster than in the free ligand. The observed rate acceleration, and the results of solution i.r. studies, are consistent with a weak interaction between the metal ion and the carbonyl group of the ester. Base hydrolysis involves nucleophilic attack by ‘ external ’ hydroxide rather than attack by a hydroxide ion co-ordinated to CuII. The preparation of sodium salts of the partial esters Me3edta–, Me2edta2–, and Meedta3– is described.Keywords
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