Enols Are Common Intermediates in Hydrocarbon Oxidation
Craig A. Taatjes,1,2*
Nils Hansen,1
Andrew McIlroy,1
James A. Miller,1
Juan P. Senosiain,1
Stephen J. Klippenstein,1
Fei Qi,1,3
Liusi Sheng,3
Yunwu Zhang,3
Terrill A. Cool,4
Juan Wang,4
Phillip R. Westmoreland,5
Matthew E. Law,5
Tina Kasper,6
Katharina Kohse-Höinghaus6
Models for chemical mechanisms of hydrocarbon oxidation rely on spectrometric identification of molecular structures in flames. Carbonyl (keto) compounds are well-established combustion intermediates. However, their less-stable enol tautomers, bearing OH groups adjacent to carbon-carbon double bonds, are not included in standard models. We observed substantial quantities of two-, three-, and four-carbon enols by photoionization mass spectrometry of flames burning representative compounds from modern fuel blends. Concentration profiles demonstrate that enol flame chemistry cannot be accounted for purely by keto-enol tautomerization. Currently accepted hydrocarbon oxidation mechanisms will likely require revision to explain the formation and reactivity of these unexpected compounds.
1 Combustion Research Facility, Mail Stop 9055, Sandia National Laboratories, Livermore, CA 94551–0969, USA.
2 JILA, National Institute of Standards and Technology and University of Colorado, 440CB, Boulder CO, 80309–0440 USA.
3 National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230026, China.
4 School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853, USA.
5 Department of Chemical Engineering, University of Massachusetts, Amherst, MA 01003–9303, USA.
6 Physikalische Chemie I, Universität Bielefeld, Universitätsstraße 25, 33615 Bielefeld, Germany.
* To whom correspondence should be addressed. E-mail: cataatj{at}sandia.gov
