Pyruvic acid (PA) is a key intermediate in the keto-acid chemistry of atmospheric aerosols. Currently, fundamental understanding of PA degradation in gas and aqueous phase is still lacking. In this work, the energetics of PA degradation pathways in gas and aqueous phase and the temporal dependence of each species were studied theoretically. The acetaldehyde production via PA decarboxylation is found to be the dominant channel. In the aqueous phase however, the absence of enol isomerization pathways to vinyl alcohol-CO2 complex reduces the available acetaldehyde channels. Also, the minor CO loss through acetic acid production in aqueous phase passes through a PA hydrogen-transferred tautomer instead of going directly to α-lactone. Methylhydroxycarbene (MHC)-CO2 complex formation is the least hindered channel as confirmed by the temporal dependence calculation using RRKM where the initial abrupt decay of PA is caused by rapid MHC-CO2 accumulation. One hundred percent degradation of PA at 100 fs requires higher energy in the aqueous phase. Consequently, the exit channel ratio of acetaldehyde to acetic acid decreased in aqueous phase at reaction completion, assumed to be within 1 s. The calculated RRKM rates of PA decomposition agree with the previous gas-phase experiments. Slower rates are observed for aqueous phase due to higher energy barriers. PA degradation is also faster than methylglyoxal (MGY) decomposition and 2,2-dihydroxypropionic acid (DHPA) formation in gas phase, calculated using TST between 400-1000 K. The unsymmetrical Eckart tunneling is only significant in DHPA formation and MGY production. In aqueous phase, DHPA formation becomes competitive with PA degradation at lower temperatures while MGY decomposition rate rapidly increases with temperature, surpassing DHPA formation and approaching PA degradation at 1000 K.

Ground state potential energy surface and statistical kinetics of pyruvic acid degradation in gas and aqueous phase

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.