On N-acetylcysteine. Part II. Oxidation of N-acetylcysteine by hydrogen peroxide: Kinetic study of the overall process

Article abstract of DOI:10.1139/v94-267

The oxidation kinetics of N-acetylcysteine (RSH) by hydrogen peroxide has been studied at neutral pH at different concentration ratios from 0.2 to 20 (4 x 10^-4 mol L^-1 ≤ [RSH]₀ ≤ 2 x 10^- mol L^-1, 10^-4 mol L^-1 ≤ [H₂O₂]₀ ≤ 10^-2 mol L^-1). In all the cases studied, N-acetyleystine (RSSR) is the only oxidized product formed. Our kinetic data have focused on the importance of the concentration ratio to reach the stoichiometric oxidation of N-acetylcysteine by hydrogen peroxide. Indeed non-stoichiometric oxidation of RSH occurs at relatively low concentration ratios (R < 2.5) whereas stoichiometric oxidation is observed when R > 2.5. Moreover, it has been shown that in the first minutes of the reaction there is the formation of a complex between RSH and H₂O₂, the stoichiometry of the complex being RSH concentration-dependent for a given R (R > 2.5). Reaction mechanisms have been quantitatively established and the k values of each step determined.