Low-Temperature NMR Characterization of Reaction of Sodium Pyruvate with Hydrogen Peroxide

It was proposed that the reaction of sodium pyruvate and H2O2 generates the intermediate 2-hydroperoxy-2-hydroxypropanoate, which converts into acetate, CO2, and H2O (Aleksankin et al. Kernenergie 1962, 5, 362-365). These conclusions were based on the products generated in O-18-enriched water and H2O2 reacting with pyruvic acid at room temperature; however, the lifetime of 2-hydroperoxy-2-hydroxypropanoate at room temperature is too short for direct spectroscopic observation. Therefore, we applied the combination of low-temperature and C-13 NMR techniques to verify, for the first time, the formation of 2-deuteroperoxy-2-deuteroxypropanoate in mixtures of D2O and methanol-d4 and to monitor directly each species involved in the reaction between D2O2 and C-13-enriched pyruvate. Our NMR results confirm the formation of 2-deuteroperoxy-2-deuteroxypropanoate, where the respective chemical shifts are supported by density functional theory (DFT) calculations. At near-neutral apparent pD (pD*) and -35 degrees C, the formation of 2-deuteroperoxy-2-deuteroxypropanoate occurred with k = 2.43 x 103 dm(-3)mol(-1)s(-1). The subsequent decomposition of 2-deuteroperoxy-2-deuteroxypropanoate into acetate, CO2, and D2O occurred with k = 2.58 x 10(-4) s(-1) at -35 degrees C. In order to provide a full kinetic analysis, we also monitored the equilibrium of pyruvate and methanol with the hemiacetal (2-deuteroxy-2-methoxypropanoate). The kinetics for the reaction of sodium pyruvate and D2O2 were fitted by taking into account all these equilibria and species.