title: Mechanism of Decarboxylation of Pyruvic Acid in the Presence of Hydrogen Peroxide.
abstract: The purpose of this work was to probe the rate and mechanism of rapid decarboxylation of pyruvic acid in the presence of hydrogen peroxide (H2O2) to acetic acid and carbon dioxide over the pH range 2-9 at 25 °C, utilizing UV spectrophotometry, high performance liquid chromatography (HPLC), and proton and carbon nuclear magnetic resonance spectrometry ((1)H, (13)C-NMR). Changes in UV absorbance at 220 nm were used to determine the kinetics as the reaction was too fast to follow by HPLC or NMR in much of the pH range. The rate constants for the reaction were determined in the presence of molar excess of H2O2 resulting in pseudo first-order kinetics. No buffer catalysis was observed. The calculated second-order rate constants for the reaction followed a sigmoidal shape with pH-independent regions below pH 3 and above pH 7 but increased between pH 4 and 6. Between pH 4 and 9, the results were in agreement with a change from rate-determining nucleophilic attack of the deprotonated peroxide species, HOO(-), on the α-carbonyl group followed by rapid decarboxylation at pH values below 6 to rate-determining decarboxylation above pH 7. The addition of H2O2 to ethyl pyruvate was also characterized.
authors.affiliation: Department of Pharmaceutical Chemistry, The University of Kansas, Lawrence, Kansas 66047.
authors.forename: Antonio
authors.initials: A
authors.lastname: Lopalco
authors.affiliation: Department of Pharmaceutical Chemistry, The University of Kansas, Lawrence, Kansas 66047.
authors.forename: Gautam
authors.initials: G
authors.lastname: Dalwadi
authors.affiliation: Department of Pharmaceutical Chemistry, The University of Kansas, Lawrence, Kansas 66047.
authors.forename: Sida
authors.initials: S
authors.lastname: Niu
authors.affiliation: Department of Pharmaceutical Chemistry, The University of Kansas, Lawrence, Kansas 66047.
authors.forename: Richard L
authors.initials: RL
authors.lastname: Schowen
authors.affiliation: Nuclear Magnetic Resonance Laboratory, Lawrence, Kansas 66045.
authors.forename: Justin
authors.initials: J
authors.lastname: Douglas
authors.affiliation: Department of Pharmaceutical Chemistry, The University of Kansas, Lawrence, Kansas 66047. Electronic address: stella@ku.edu.
authors.forename: Valentino J
authors.initials: VJ
authors.lastname: Stella
mesh_terms: D002851:Chromatography, High Pressure Liquid / Q000379:methods; D003653:Decarboxylation; D006861:Hydrogen Peroxide / Q000032:analysis / Q000737:chemistry* / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D019289:Pyruvic Acid / Q000032:analysis / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D019289:Pyruvic Acid; D006861:Hydrogen Peroxide
keywords: NMR spectroscopy; UV/Vis spectroscopy; antioxidants; chemical stability; hydration; hydrogen peroxide; kinetics; mathematical model; peroxide scavenger; pyruvic acid