Decomposition of <i>N</i>‑Chloroglycine in Alkaline Aqueous Solution: Kinetics and Mechanism

Abstract

The decomposition kinetics and mechanism of <i>N</i>-chloroglycine (MCG) was studied under very alkaline conditions ([OH^–] = 0.01–0.10 M). The absorbance change is consistent with two consecutive first-order processes in the 220–350 nm wavelength range. The first reaction is linearly dependent on [OH^–] and interpreted by the formation of a carbanion from MCG in an equilibrium step (<i>K</i>_OH) and a subsequent loss of chloride ion from this intermediate: <i>k</i>_obs1 = <i>K</i>_OH <i>k</i>₁ = (6.4 ± 0.1) × 10^–2 M^–1 s^–1, <i>I</i> = 1.0 M (NaClO₄), and <i>T</i> = 25.0 °C. The second process is assigned to the first-order decomposition of <i>N</i>-oxalylglycine, which is also formed as an intermediate in this system: <i>k</i>_obs2 = (1.2 ± 0.1) × 10^–3 s^–1. Systematic ¹H and ¹³C NMR measurements were performed in order to identify and follow the concentration changes of the reactant, intermediate, and product. It is confirmed that the decomposition proceeds via the formation of glyoxylate ion and produces <i>N</i>-formylglycine as a final product. This compound is stable for an extended period of time but eventually hydrolyses into formate and glycinate ions. A detailed mechanism is postulated which resolves the controversies found in earlier literature results