Chemical Equilibria and Kinetics in Aqueous Solutions of Zymonic Acid

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.