Chemical Equilibria and Kinetics in Aqueous Solutions of Zymonic Acid

Abstract

The chemistry of pyruvic acid is of great interest due to its essential role in metabolism for all life and its role in atmospheric chemistry. Pyruvic acid under a wide range of conditions, including normal storage conditions, will spontaneously dimerize to form zymonic acid. We isolated zymonic acid and, using a variety of 1D and 2D NMR techniques, identified it as a single structure as a solid or dissolved in DMSO. When in aqueous solution, however, we identified a mixture of five different tautomers and hydrates in equilibrium with each other with no single dominant form. The kinetics of this conversion were studied in situ via NMR. The reactivity of the tautomers and hydrates in aqueous solution is investigated and discussed in terms of aqueous reaction mechanisms. There is strong evidence for a direct, reversible conversion from an enol to a geminal diol without passing through a ketone intermediate, which implies the reversible addition of water across a double bond under ambient conditions. Additionally, there is evidence for a base catalyzed lactone ring formation, which is in essence a base catalyzed esterification reaction. The equilibrium between pyruvic acid and its oligomers in aqueous solution is of consequence in the natural environment.

Mechanistic Description of Photochemical Oligomer Formation from Aqueous Pyruvic Acid

“…Of the equilibrium species of zymonic acid in aqueous solution, these structures are the favored species. 66 In our analysis of the MS data (see Table 1 and Supporting Information, Table S1), we applied a conservative intensity threshold of 10 4 counts for analyte identifications to avoid incorrect ion assignments to noise peaks (see Experimental Section for more detail). The ions that correspond to parapyruvic acid and the closed zymonic diol are consistently observed above this threshold for the 10 mM pyruvic acid solutions before irradiation.…”

Environmental Processing of Lipids Driven by Aqueous Photochemistry of α-Keto Acids

“…Pyruvic acid was distilled at <55 °C and used within one month of distillation to ensure oligomers from dark processes were minimized. 77 Hexanol was heated to ∼50 °C, hexanoic acid to ∼80 °C, and nonanoic acid and nonanol were heated to ∼180 °C during distillation. In each case noticeable yellow impurities were removed upon distillation, leaving a clear, colorless liquid.…”

Electrochemistry for the Generation of Renewable Chemicals: One‐Pot Electrochemical Deoxygenation of Xylose to δ‐Valerolactone

“…The products can also undergo av ariety of ester formations through their hydroxyl,aldehyde, and acid groups. [41][42][43][44] To ascertain that the observed product selectivities result from the electro-generated oxidant, the oxidation of 1,2-propanediolw as repeated using HCl and H 2 SO 4 as electrolyte. The product profile obtained with HCl was nearly identicalt ot hat of NaCl but different from that obtained using H 2 SO 4 as electrolyte (see the Supporting Information).…”