Unimolecular Decomposition of Pyruvic Acid: An Experimental and Theoretical Study

Photochemistry of aqueous pyruvic acid

“…Assuming these calculations to be at least qualitatively correct, it seems likely that the UV photochemistry of PA with light of λ > 300 nm proceeds according to the sequence S 0 → S 1 → T 2 → T 1 . This intersystem crossing to the triplet surface is markedly different from the gas phase photochemistry, which occurs solely on the singlet surface to generate methylhydroxycarbene (28)(29)(30)54). However, in the aqueous study presented here, PA is seen to react from its T 1 state to produce acetoin, lactic and acetic acids, and oligomers, as described below and depicted in Scheme 1.…”

“…PA undergoes decarboxylation in the gas and aqueous phases by means of different mechanisms. Decarboxylation of gas phase PA has been seen to occur thermochemically, through IR multiphoton pyrolysis, as well as through UV and visible excitation (13,(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36). The main removal pathway of gas phase PA from the troposphere is UV photolysis, with reaction with OH radical providing a minor contribution (31).…”

A potential energy profile of the catalytic cycle of pyruvate decarboxylase

“…The rate-determining step for this process is clearly the loss of CO 2 from reagent cluster 1 u , requiring at least 52.94 kcal•mol -1 , and making the rate for the uncatalyzed decarboxylation of pyruvic acid virtually negligible. Saito [32] reports an experimental decarboxylation barrier for pyruvic acid in the gas phase at 850 -1000 K of 40.0 kcal•mol -1 . The corresponding calculated barrier at the HF/6-3lG**//HF/ 3-21G level of theory is 40.8 kcal•mol -1 .…”

Evolution of Selected Isoprene Oxidation Products in Dark Aqueous Ammonium Sulfate

“…Moreover, we did not observe any significant decarboxylation with any of the sodium salts, therefore, the documented mechanism for gas phase decarboxylation [Takahashi et al, 2008] is unlikely to be applicable to the aqueous phase decarboxylation in the presence of the ammonium salts. One of the studies of gas phase thermal dissociation of pyruvic acid showed that decarboxylation happens through a transition state with a 5-member ring formation [Saito et al, 1994], but it is not very clear how ammonium/ammonia can contribute to that kind of pathway. However the observations of CO2 production from pyruvic acid and glyoxylic shows a potential concerted pathway of the transfer of hydrogen and cleavage of the carbon-carbon bond.…”

“…Similar results are anticipated for glyoxylic acid. In addition, the fragmentation (carbon-carbon bond cleavage) of pyruvic acid in the gas and aqueous phases has been studied widely, including: thermal decarboxylation [Saito et al, 1994;Yamamoto and Back, 1985], infrared and near infrared multiphoton photolysis [Larsen and Vaida, 2012;Plath et al, 2009;Takahashi et al, 2008], UV-Vis induced photolysis [Griffith et al, 2013;Guzmán et al, 2006aGuzmán et al, , 2006bLeermakers and Vesley, 1963;Reed Harris et al, 2014;Yamamoto and Back, 1985] and oxidation by hydroxyl radical [Boris et al, 2014;Mellouki and Mu, 2003]. However, neither pyruvic acid nor glyoxylic acid was studied in the dark aqueous phase in the presence of atmospherically relevant inorganic salts.…”