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Photoinduced Oligomerization of Aqueous Pyruvic Acid

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.

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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.

Item Type:Article
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URLURL TypeDescription
Guzmán, M. I.0000-0002-6730-7766
Colussi, A. J.0000-0002-3400-4101
Hoffmann, M. R.0000-0001-6495-1946
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
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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
Deposited By: George Porter
Deposited On:28 Jul 2015 21:55
Last Modified:09 Mar 2020 13:18

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