Guzmán, M. I. and Colussi, A. J. and Hoffmann, M. R. (2006) Photoinduced Oligomerization of Aqueous Pyruvic Acid. Journal of Physical Chemistry A, 110 (10). pp. 3619-3626. ISSN 1089-5639. https://resolver.caltech.edu/CaltechAUTHORS:20150623-154754586
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Abstract
The 320 nm-band photodecarboxylation of aqueous pyruvic acid (PA), a representative of the α-oxocarboxylic acids widely found in the atmospheric aerosol, yields 2,3-dimethyltartaric (A) and 2-(3-oxobutan-2-yloxy)-2-hydroxypropanoic (B) acids, rather than 3-hydroxy-2-oxobutanone as previously reported. A and B are identified by liquid chromatography with UV and ESI-MS detection, complemented by collisionally induced dissociation and ^2H and ^(13)C isotope labeling experiments. The multifunctional ether B gives rise to characteristic δ ∼ 80 ppm ^(13)C NMR resonances. Product quantum yields are proportional to [PA](a + [PA])^(-1) in the range [PA] = 5−100 mM. CO_2(g) release rates are halved, while A and B are suppressed by the addition of >1.5 mM TEMPO. A and B are only partially quenched in air-saturated solutions. These observations are shown to be consistent with an oligomerization process initiated by a bimolecular reaction between ^3PA* and PA producing ketyl, CH_3Ċ(OH)C(O)OH, and acetyl, CH_3C(O)·, radicals, rather than by the unimolecular decomposition of ^3PA* into 1-hydroxyethylidene, ^3HO(CH_3)C: (+CO_2), or [CH_3C(O)· + ·C(O)OH] pairs. A arises from the dimerization of ketyl radicals, while B ensues the facile decarboxylation of the C_8β-ketoacid formed by association of acetyl radicals with the ketyl radical adduct of PA. Since the radical precursors to A and B are scavenged by O2 with a low probability per encounter (ksc ∼ 1 × 10^6 M^(-1) s^(-1)), PA is able to accrete into multifunctional polar species in aerated aqueous media under solar illumination.
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Additional Information: | © 2006 American Chemical Society. Received: October 24, 2005; In Final Form: January 10, 2006. This work was financed by NSF Grant ATM-0228140. This project benefited from the use of instrumentation made available by the Caltech Environmental Analysis Center. N. Dalleska provided valuable assistance with chromatographic analysis. | |||||||||
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Issue or Number: | 10 | |||||||||
Record Number: | CaltechAUTHORS:20150623-154754586 | |||||||||
Persistent URL: | https://resolver.caltech.edu/CaltechAUTHORS:20150623-154754586 | |||||||||
Official Citation: | Photoinduced Oligomerization of Aqueous Pyruvic Acid M. I. Guzmán, A. J. Coluss, and M. R. Hoffmann The Journal of Physical Chemistry A 2006 110 (10), 3619-3626 DOI: 10.1021/jp056097z | |||||||||
Usage Policy: | No commercial reproduction, distribution, display or performance rights in this work are provided. | |||||||||
ID Code: | 58472 | |||||||||
Collection: | CaltechAUTHORS | |||||||||
Deposited By: | George Porter | |||||||||
Deposited On: | 28 Jul 2015 21:55 | |||||||||
Last Modified: | 09 Mar 2020 13:18 |
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