Submitted on March 21, 2005
Accepted on April 29, 2005
Enols Are Common Intermediates in Hydrocarbon Oxidation
Craig A. Taatjes 1*,
Nils Hansen 2,
Andrew McIlroy 2,
James A. Miller 2,
Juan P. Senosiain 2,
Stephen J. Klippenstein 2,
Fei Qi 3,
Liusi Sheng 4,
Yunwu Zhang 4,
Terrill A. Cool 5,
Juan Wang 5,
Phillip R. Westmoreland 6,
Matthew E. Law 6,
Tina Kasper 7,
Katharina Kohse-Höinghaus 7
1 Combustion Research Facility, Mail Stop 9055, Sandia National Laboratories, Livermore, CA 94551-0969 USA; JILA, National Institute of Standards and Technology and University of Colorado, 440CB, Boulder CO, 80309-0440 USA.
2 Combustion Research Facility, Mail Stop 9055, Sandia National Laboratories, Livermore, CA 94551-0969 USA.
3 Combustion Research Facility, Mail Stop 9055, Sandia National Laboratories, Livermore, CA 94551-0969 USA; National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230026, China.
4 National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230026, China.
5 School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853 USA.
6 Department of Chemical Engineering, University of Massachusetts, Amherst, MA 01003-9303 USA.
7 Physikalische Chemie I, Universität Bielefeld, Universitätsstraße 25, 33615 Bielefeld, Germany.
* To whom correspondence should be addressed.
Craig A. Taatjes , E-mail: cataatj{at}sandia.gov
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. Here we observe significant quantities of 2, 3, and 4-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.
