Decomposition of Pyruvic Acid on the Ground-State Potential Energy Surface

Abstract

A potential energy surface is reported for isomerization and decomposition of gas-phase pyruvic acid (CH3C(O)C(O)OH) in its ground electronic state. Consistent with previous works, the lowest energy pathway for pyruvic acid decomposition is identified as decarboxylation to produce hydroxymethylcarbene (CH3COH), with overall barrier of 43 kcal mol(-1). This study discovers that pyruvic acid can also isomerize to the α-lactone form with a barrier of only 36 kcal mol(-1), from which CO elimination can occur at 49 kcal mol(-1) above pyruvic acid. An additional novel channel is identified for the tautomerisation of pyruvic acid to the enol form, via a double H-shift mechanism. The barrier for this process is 51 kcal mol(-1), which is around 20 kcal mol(-1) lower than the barrier for conventional keto-enol tautomerization via a 1,3-H shift transition state. Rate coefficients are calculated for pyruvic acid decomposition through RRKM theory/master equation simulations at 800-2000 K and 1 atm, showing good agreement with the available experimental data. The dissociation of vibrationally excited pyruvic acid produced through photoexcitation and subsequent internal conversion to the ground state is also modeled under tropospheric conditions and is seen to produce appreciable quantities of CO (∼1-4%) in addition to CH3COH via the dominant CO2 loss channel.

Photoisomerization of Methyl Vinyl Ketone and Methacrolein in the Troposphere: A Theoretical Investigation of Ground-State Reaction Pathways

“…In addition to the dissociation channels, two tautomerization pathways exist for MVK, which produce the enols 1-hydroxymethylallene (1-HMA) and 2-hydroxybutadiene (2-HBD) through 1,3-H shifts via TS3 and TS4 respectively. The formation of 2-HBD through keto–enol tautomerization has a particularly low barrier (63.8 kcal mol –1 ), − which we attribute to the conjugated structure of the enol product (a similar enol form has recently been reported for pyruvic acid) . This low barrier, coupled with the relatively small reaction endothermicity (9.4 kcal mol –1 ), makes 2-HBD a likely candidate for isomerization with subsequent collisional deactivation.…”

Gas-Phase Photolysis of Pyruvic Acid: The Effect of Pressure on Reaction Rates and Products

“…Further, although both CO and 13 CO were produced, 13 CO was present in approximately equal concentration to acetic acid (Table ). While these results are not unequivocally conclusive, they are consistent with the mechanism described by Da Silva …”

“…Yamamoto and Back (1983) imply the major process is on the S 1 surface, but they do not explicitly consider the possibility of decarboxylation on S 0 . Experimental and computational work regarding vibrational overtones of pyruvic acid demonstrate that S 0 chemistry can yield CO 2 and acetaldehyde. − , …”

Infrared spectroscopy of 2-oxo-octanoic acid in multiple phases

“…6,16 Its photochemical products, reaction rates, and reaction mechanisms have been determined. 3,4,[16][17][18][19][20][21][22][23][24][25][26][27] The effect of water on its conformer distribution has also been experimentally and computationally investigated and its effect on PA's chemistry reported. 1,[28][29][30][31][32][33] Oxoacids are also found in oceans and aerosol particles, and their aqueous phase photochemistry has been extensively investigated.…”