Kinetic and Mechanistic Studies of the N-Bromosuccinimide-Promoted Oxidative Decarboxylation of Glycine, DL-Alanine, and DL-Valine

Article abstract of DOI:10.1021/jo00208a012

The kinetics of the oxidative decarboxylation of glycine (1a), DL-alanine (1b), and DL-valine (1c) promoted by N-bromosuccinimide (NBS) have been studied as a function of pH.The pH-rate profile for 1a is bell-shaped while those for 1b and 1c exhibit an inverted-bell shape.At pH 3.7, 1a exhibits Michaelis-Menten kinetic behavior but shows substrate inhibition at pH 5.0.Both 1b and 1c display zero-order dependence on substrate concentration at pH 3.7 but exhibit Michaelis-Menten behavior at pH 5.0.The oxidation of 1a is characterized by a solvent deuterium isotope effect of k(H2O)/k(D2O) = 2.0 and a secondary deuterium isotope effect (glycine-d₅) of k_H/k_D = 1.35.Proton inventories with glycine under two different sets of conditions both exhibit significant downward curvature with negative curvature parameters.A mechanism involving the formation of an acyl hypobromite of 1a, its slow decomposition to an imine, and subsequent rapid conversion of imine to products is proposed.Both 1b and 1c undergo oxidation by a mechanism involving the slow abstraction of the α hydrogen as hydride ion from the substrate as well as its acyl hypobromite to give the imine.