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

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-degrees-C and l = 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 = k(obs) = (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.