<b>The Photochemistry of α-Keto Acids and α-Keto Esters. I. Photolysis of Pyruvic Acid and Benzoylformic Acid</b>

Leermakers, Peter A.; Vesley, George F.

doi:10.1021/ja00906a013

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“…In addition to acetoin and lactic and acetic acids, small oligomers (dimers) were observed in this work, in the previous work by Guzman et al (13) in aqueous solution, and by Leermakers and Vesley (37) in organic solvents. Reaction 5 of Scheme 1 shows the generation of 2,3-dimethyltartaric acid, presumably in both meso-and DL diastereomers, from the reaction between two molecules of the prevalent radical intermediate (PA•).…”

Section: Discussionsupporting

confidence: 78%

“…Photodecarboxylation of aqueous PA is facilitated through excitation of its n→π* band, with an absorption maximum of 321 nm (37). This decarboxylation has been known for many years, but the mechanism and resulting products have been controversial (13,(37)(38)(39).…”

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confidence: 99%

“…This decarboxylation has been known for many years, but the mechanism and resulting products have been controversial (13,(37)(38)(39). Earlier studies performed by Leermakers and Vesley (37,38) report 3-hydroxy-2-butanone (acetoin) as the only isolable product from the aqueous photolysis of PA.…”

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Photochemistry of aqueous pyruvic acid

Griffith

Carpenter

Shoemaker³

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

125

289

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The study of organic chemistry in atmospheric aerosols and cloud formation is of interest in predictions of air quality and climate change. It is now known that aqueous phase chemistry is important in the formation of secondary organic aerosols. Here, the photoreactivity of pyruvic acid (PA; CH 3 COCOOH) is investigated in aqueous environments characteristic of atmospheric aerosols. PA is currently used as a proxy for α-dicarbonyls in atmospheric models and is abundant in both the gas phase and the aqueous phase (atmospheric aerosols, fog, and clouds) in the atmosphere. The photoreactivity of PA in these phases, however, is very different, thus prompting the need for a mechanistic understanding of its reactivity in different environments. Although the decarboxylation of aqueous phase PA through UV excitation has been studied for many years, its mechanism and products remain controversial. In this work, photolysis of aqueous PA is shown to produce acetoin (CH 3 CHOHCOCH 3 ), lactic acid (CH 3 CHOHCOOH), acetic acid (CH 3 COOH), and oligomers, illustrating the progression from a three-carbon molecule to four-carbon and even six-carbon molecules through direct photolysis. These products are detected using vibrational and electronic spectroscopy, NMR, and MS, and a reaction mechanism is presented accounting for all products detected. The relevance of sunlight-initiated PA chemistry in aqueous environments is then discussed in the context of processes occurring on atmospheric aerosols.

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confidence: 78%

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Photochemistry of aqueous pyruvic acid

Griffith

Carpenter

Shoemaker³

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

125

289

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“…Although triplet pyruvic acid has been found to abstract hydrogen with a rate similar to benzophenone triplet in various alcohols (12) and thus hydrogen abstraction from ascorbate anion could account for the reaction leading to CIDEP of the primary radicals, it must be recognized that the reaction could also proceed rapidly via an electron-transfer mechanism: In the initial series of experiments the pH of the solutions was at 3.5, so that appreciable concentrations of both the unionized pyruvic acid and the pyruvate anion could be involved in the photooxidation of vitamin C. The triplet property of the unionized pyruvic acid is not expected to be different from that of the triplet pyruvate anion. By adjusting the pH of the solution to 10.2 using KOH, the concentrations of the pyruvate anion and the ascorbate anion would be greatly enhanced so that the actual photooxidation is now represented by the reaction This presents an interesting opportunity to study the photochemical reaction between two anions and at this time there is no compelling argument that reaction [7] should proceed via an electrontransfer from the ascorbate anion to the excited pyruvate anion as an efficient means to preserve the initial polarization later developed in the observed radicals.…”

Section: Resultsmentioning

confidence: 99%

An electron spin resonance and time-resolved CIDEP study of the oxidation of ascorbic acid by pyruvic acid, duroquinone, and vitamin K₁

Depew¹,

Adeleke²,

Wan³

1981

Can. J. Chem.

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. Can. J. Chem. 59,2708 (1981).The photooxidation of vitamin C by pyruvic acid and its derivatives, duroquinone, and vitamin K, is systematically studied by the combined esr and time-resolved CIDEP technique. Because of the unique property of the triplet pyruvic acid which is different from that of the duroquinone triplet, the choice of these model systems allowed the CIDEP observations of the initial polarization of the ascorbate radical anion and its counter primary radical in either the enhanced absorptive or the emissive mode. The results demonstrate the efficient photooxidation of vitamin C by the triplet vitamin K, and that the latter triplet possesses similar properties as the triplet quinones. In the photooxidation system involving vitamin C and pyruvic acid, the adjustment of the pH ofthe aqueous solution afforded an opportunity to observe the photochemical reaction between two anions, the pyruvate anion and the ascorbate anion. Arguments were made in favor of an electron transfer mechanism for the oxidation of vitamin C by triplet vitamin K, but against the electron transfer mechanism for the oxidation of vitamin C by triplet pyruvate anion. T, values of the primary radicals estimated from their CIDEP transient responses at low microwave power are reported and it was suggested that the hydrogenbonding capacity of the ascorbate radical anion in water does not contribute significantly to the relative difference of Ti's between itself and the counter pyruvic ketyl radical.M. CATHERINE DEPEW, BABATUNDE B. ADELEKE et JEFFREY K. S. WAN. Can. J. Chem. 59,2708 (1981). En faisant appel la rpe combinke a la technique de PEDIC resolue en fonction du temps, on Ctudie systkmatiquement la photooxydation de la vitamine C par l'acide pyruvique et ses derives, par la duroquinone et par la vitamine K,. Compte tenu de la propriete unique du triplet de I'acide pyruvique qui est differente de celle du triplet de la duroquinone, le choix de ces modeles permet des observations de PEDIC de la polarisation initiale de I'anion radical ascorbate et de son radical primaire oppose lors de I'absorption ou de I'emission. Les resultats demontrent I'efficacite de la photooxydation de la vitamine C par le triplet de la vitamine K, et que le dernier triplet possede des propriCtCs identiques a celles du triplet des quinones. Dans la photooxydation qui implique la vitamine C et I'acide pyruvique, I'ajustement du pH de la solution aqueuse fournit I'opportunitk d'observer la reaction photochimique entre deux anions, I'anion pyruvate et I'anion ascrobate. On suggere un mecanisme par transfec d'tlectrons pour I'oxydation de la vitamine C par le triplet de la vitamine K,, mais on n'admet pas ce mecanisme dans le cas de I'oxydation de la vitamine C par le triplet de I'anion pyruvate. On rapporte les valeurs de T, des radicaux primaires evalues a partir de leurs reponses intermediaires en PEDIC en microondes de faible puissance, et on suggere que la capacite en liaison hydrogenes de I'anion radical ascorbate dans I'eau ne contribue pas de f a~o ...

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“…When examined in its entirety, the evidence for the production of acetoin, lactic, and acetic acids in PA photolysis is irrefutable, and the mechanism presented is sound, being grounded in theoretical calculations as well as supported by the older literature (5,6), and providing an alternative explanation of Guzman et al's prior published results (3,4).…”

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Reply to Eugene et al.: Photochemistry of aqueous pyruvic acid

Griffith

Carpenter

Shoemaker³

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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The Photochemistry of α-Keto Acids and α-Keto Esters. I. Photolysis of Pyruvic Acid and Benzoylformic Acid

Cited by 121 publications

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Photochemistry of aqueous pyruvic acid

Photochemistry of aqueous pyruvic acid

An electron spin resonance and time-resolved CIDEP study of the oxidation of ascorbic acid by pyruvic acid, duroquinone, and vitamin K₁

Reply to Eugene et al.: Photochemistry of aqueous pyruvic acid

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The Photochemistry of α-Keto Acids and α-Keto Esters. I. Photolysis of Pyruvic Acid and Benzoylformic Acid

Cited by 121 publications

References 0 publications

Photochemistry of aqueous pyruvic acid

Photochemistry of aqueous pyruvic acid

An electron spin resonance and time-resolved CIDEP study of the oxidation of ascorbic acid by pyruvic acid, duroquinone, and vitamin K1

Reply to Eugene et al.: Photochemistry of aqueous pyruvic acid

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An electron spin resonance and time-resolved CIDEP study of the oxidation of ascorbic acid by pyruvic acid, duroquinone, and vitamin K₁