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

Abstract

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 firstmore » 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.« less

Authors:
ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1];  [2]; ORCiD logo [3];  [1]; ORCiD logo [1]
  1. Univ. of Colorado, Boulder, CO (United States)
  2. Kapteyn-Murnane Lab. Inc. (KMLabs Inc.), Boulder, CO (United States)
  3. Univ. of Colorado, Boulder, CO (United States); Kapteyn-Murnane Lab. Inc. (KMLabs Inc.), Boulder, CO (United States)
Publication Date:
Research Org.:
Univ. of Colorado, Boulder, CO (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
OSTI Identifier:
1778226
Alternate Identifier(s):
OSTI ID: 1777018
Grant/Contract Number:  
SC0018627; FG02-99ER14982; DGE-1650115; DGE-1144083
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Proceedings of the Combustion Institute
Additional Journal Information:
Journal Volume: 38; Journal Issue: 1; Journal ID: ISSN 1540-7489
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; VUV light source; Keto-enol tautomerization; Isomer detection; Tabletop tunable VUV; Enol intermediates

Citation Formats

Couch, David E., Nguyen, Quynh L. D., Liu, Allison, Hickstein, Daniel D., Kapteyn, Henry C., Murnane, Margaret M., and Labbe, Nicole J. Detection of the keto-enol tautomerization in acetaldehyde, acetone, cyclohexanone, and methyl vinyl ketone with a novel VUV light source. United States: N. p., 2020. Web. doi:10.1016/j.proci.2020.06.139.
Couch, David E., Nguyen, Quynh L. D., Liu, Allison, Hickstein, Daniel D., Kapteyn, Henry C., Murnane, Margaret M., & Labbe, Nicole J. Detection of the keto-enol tautomerization in acetaldehyde, acetone, cyclohexanone, and methyl vinyl ketone with a novel VUV light source. United States. https://doi.org/10.1016/j.proci.2020.06.139
Couch, David E., Nguyen, Quynh L. D., Liu, Allison, Hickstein, Daniel D., Kapteyn, Henry C., Murnane, Margaret M., and Labbe, Nicole J. 2020. "Detection of the keto-enol tautomerization in acetaldehyde, acetone, cyclohexanone, and methyl vinyl ketone with a novel VUV light source". United States. https://doi.org/10.1016/j.proci.2020.06.139. https://www.osti.gov/servlets/purl/1778226.
@article{osti_1778226,
title = {Detection of the keto-enol tautomerization in acetaldehyde, acetone, cyclohexanone, and methyl vinyl ketone with a novel VUV light source},
author = {Couch, David E. and Nguyen, Quynh L. D. and Liu, Allison and Hickstein, Daniel D. and Kapteyn, Henry C. and Murnane, Margaret M. and Labbe, Nicole J.},
abstractNote = {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.},
doi = {10.1016/j.proci.2020.06.139},
url = {https://www.osti.gov/biblio/1778226}, journal = {Proceedings of the Combustion Institute},
issn = {1540-7489},
number = 1,
volume = 38,
place = {United States},
year = {2020},
month = {9}
}

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