Kinetics and mechanism of the multi-step oxidation of ethylenediaminetetraacetate by [Ag(OH)4]- in alkaline media

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Alkaline solutions of [Ag(OH)4]- oxidise ethylenediaminetetraacetate (edta) in a multistep sequence which produces iminodiacetate (ida), glycinate and glycolate ions, and eventually ammonia, formaldehyde, carbon dioxide and water. The reaction shows changing stoichiometry and product distribution. At [edta]0/[Ag(OH)4-]0 = 1:1, glycinate and ida are produced in similar amounts with detectable ammonia and formaldehyde. When [edta]0/[Ag(OH)4-]0 = 200:1, very little glycinate is produced with no ammonia or formaldehyde detected. The kinetics of the oxidation was studied by the stopped-flow method at high excesses of edta and 25 °C and I = 1.2 mol dm-3. The overall rate is as in equation (i), where the coefficients, obtained by non-linear least-square analysis, are A = kobs = (A + B[OH-])[edta4-]/[OH-] + C[edta4-] (i) 4.38 ± 0.57 s-1, B = 34.8 ± 1.1 dm3 mol-1 s-1 and C = 26.3 ± 2.1. A multi-step electron-transfer mechanism is proposed involving initial C-N bond cleavage at the ethylenediamine group.

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Journal of the Chemical Society, Dalton Transactions