Summary
Base hydrolysis of methyl ethylenediaminemonoacetate has been studied at I=0.1 mol dm−3 (NaClO4) over the pH range 7.4–8.8 at 25 °C. The proton equilibria of the ligand can be represented by the equations,
where E is the free unprotonated ester species. Values of pK1 and pK2 are 4.69 andca. 7.5 at 25° (I=0.1 mol dm−3). For base hydrolysis of EH+, kOH=1.1×103 dm3 mol−1 s−1 at 25 °C. The species E is shown to undergo lactamisation to give 2-oxopiperazine (klact ca. 1×10−3 s−1) at 25 °C. Formation of the lactam is indicated both by u.v. measurements and by isolation and characterisation of the compound.
Base hydrolysis of the ester ligand in the complex [CuE]2+ has been studied over a range of pH and temperature, k 25OH =9.3×104 dm3 mol−1 s−1 with ΔH≠=107 kJ mol−1 and ΔS ≠298 =209 JK−1 mol−1. Base hydrolysis of [CuE]2+ is estimated to be some 1055 fold faster than that of the free ester ligand. The results suggest that base hydrolysis occursvia a chelate ester species in which the methoxycarbonyl group of the ligand is bonded to copper(II).
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Hay, R.W., Basak, A.K. & Pujari, M.P. Kinetics and mechanism of the copper(II) promoted hydrolysis of the methyl ester of ethylenediaminemonoacetate. Transition Met Chem 11, 27–30 (1986). https://doi.org/10.1007/BF01064497
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DOI: https://doi.org/10.1007/BF01064497