Detection of the keto-enol tautomerization in acetaldehyde, acetone, cyclohexanone, and methyl vinyl ketone with a novel VUV light source

Couch, David E.; Nguyen, Quynh L. D.; Liu, Allison; Hickstein, Daniel D.; Kapteyn, Henry C.; Murnane, Margaret M.; Labbe, Nicole J.

doi:10.1016/j.proci.2020.06.139

Detection of the keto-enol tautomerization in acetaldehyde, acetone, cyclohexanone, and methyl vinyl ketone with a novel VUV light source

Journal Article · Wed Sep 09 00:00:00 EDT 2020 · Proceedings of the Combustion Institute

DOI:https://doi.org/10.1016/j.proci.2020.06.139· OSTI ID:1778226

^[1]; ^[2]; ^[2]; Hickstein, Daniel D. ^[3]; ^[4]; Murnane, Margaret M. ^[2]; ^[2]

Univ. of Colorado, Boulder, CO (United States); CU Boulder
Univ. of Colorado, Boulder, CO (United States)
Kapteyn-Murnane Lab. Inc. (KMLabs Inc.), Boulder, CO (United States)
Univ. of Colorado, Boulder, CO (United States); Kapteyn-Murnane Lab. Inc. (KMLabs Inc.), Boulder, CO (United States)

The discovery of enols in combustion environments and our atmosphere has garnered increasing attention to the many unanswered questions surrounding enol chemistry. The scarcity of experimental data concerning these enols renders combustion and atmospheric models with a lack of constraining parameters, leading to varying computational predictions. Experimental detection is difficult because mass spectrometry, a powerful tool for probing a wide variety of species, cannot distinguish between enols and their thermodynamically favorable ketone isomers. A solution to this ambiguity is to use tunable vacuum ultraviolet (VUV) light from a synchrotron to identify the presence of the enol by its lower ionization energy compared to the isomer. We present a tabletop-scale VUV light source that implements highly cascaded harmonic generation, a new regime of cascaded nonlinear optics, to provide a set of spectral lines spaced by 1.2 eV. We demonstrate that the variety of photon energies available allows us to detect the keto-enol tautomerization of four aldehydes and ketones. By combining this novel VUV light source with an established microreactor, we first revisit the formation of vinyl alcohol from acetaldehyde and confirm that the observed isomerization is indeed unimolecular. Secondly, we observe the thermal tautomerization of acetone to propen-2-ol for the first time. Finally, we observe the thermal tautomerization of cyclohexanone to 1-cyclohexenol and methyl vinyl ketone to 2-hydroxybutadiene, where the results are in good agreement with those reported at a synchrotron. Furthermore, our measurements can be used to constrain models, inform future experimental studies of enol reactivity, and potentially enhance current understanding of combustion and environmental chemistry.

View Accepted Manuscript (DOE)

Research Organization:: Univ. of Colorado, Boulder, CO (United States)

Sponsoring Organization:: USDOE Office of Science (SC), Basic Energy Sciences (BES)

Grant/Contract Number:: SC0018627; FG02-99ER14982

OSTI ID:: 1778226

Alternate ID(s):: OSTI ID: 1777018
OSTI ID: 1907677

Journal Information:: Proceedings of the Combustion Institute, Journal Name: Proceedings of the Combustion Institute Journal Issue: 1 Vol. 38; ISSN 1540-7489

Publisher:: ElsevierCopyright Statement

Country of Publication:: United States

Language:: English

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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
Enol intermediates
Isomer detection
Keto-enol tautomerization
Tabletop tunable VUV
VUV light source

Detection of the keto-enol tautomerization in acetaldehyde, acetone, cyclohexanone, and methyl vinyl ketone with a novel VUV light source

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