Formic acid catalyzed keto-enol tautomerizations for C2 and C3 enols: Implications in atmospheric and combustion chemistry

Enols are important species in atmospheric and combustion chemistry. However, their implications in these environments are not well established due to a lack of accurate rate constants and mechanisms to determine their fate. In this work, we investigate the formic acid catalyzed keto-enol tautomerizations converting vinyl alcohol, propen-2-ol and 1-propenol into acetaldehyde, acetone and propanal, respectively. High-level ab initio and multistructural torsional variational transition state theory calculations are performed with small-curvature tunneling corrections to obtain rate constants in the temperature range 200 K-3000 K. Tunneling is shown to be pronounced as a consequence of very narrow adiabatic potential energy curves, and indicates a need to revisit previous calculations. We show the implications of the studied reactions on the fate of enols under combustion relevant conditions by detailed kinetic modeling simulations. The yield of vinyl alcohol predicted by our calculated rate constants may be useful to lessen the underestimation of organic acids concentrations in current atmospheric models.