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Title: Low temperature (550-700 K) oxidation pathways of cyclic ketones: Dominance of HO 2-elimination channels yielding conjugated cyclic coproducts

The low-temperature oxidation of three cyclic ketones, cyclopentanone (CPO; C 5H 8O), cyclohexanone (CHO; C 6H 10 O), and 2-methyl-cyclopentanone (2-Me-CPO; CH 3–C 5H7 O), is studied between 550 and 700 K and at 4 or 8 Torr total pressure. Initial fuel radicals R are formedvia fast H-abstraction from the ketones by laser-photolytically generated chlorine atoms. Intermediates and products from the subsequent reactions of these radicals in the presence of excess O 2 are probed with time and isomeric resolution using multiplexed photoionization mass spectrometry with tunable synchrotron ionizing radiation. For CPO and CHO the dominant product channel in the R + O 2 reactions is chain-terminating HO 2-elimination yielding the conjugated cyclic coproducts 2-cyclopentenone and 2-cyclohexenone, respectively. Results on oxidation of 2-Me-CPO also show a dominant contribution from HO 2-elimination. Moreover, the photoionization spectrum of the co-product suggests formation of 2-methyl-2-cyclopentenone and/or 2-cyclohexenone, resulting from a rapid Dowd–Beckwith rearrangement, preceding addition to O 2, of the initial (2-oxocyclopentyl)methyl radical to 3-oxocyclohexyl. Cyclic ethers, markers for hydroperoxyalkyl radicals (QOOH), key intermediates in chain-propagating and chain-branching low-temperature combustion pathways, are only minor products. The interpretation of the experimental results is supported by stationary point calculations on the potential energy surfaces ofmore » the associated R + O 2 reactions at the CBS-QB3 level. Furthermore, the calculations indicate that HO 2-elimination channels are energetically favored and product formation via QOOH is disfavored. Lastly, the prominence of chain-terminating pathways linked with HO 2 formation in low-temperature oxidation of cyclic ketones suggests little low-temperature reactivity of these species as fuels in internal combustion engines.« less
Authors:
 [1] ;  [2] ;  [3] ;  [1] ;  [1]
  1. Sandia National Lab. (SNL-CA), Livermore, CA (United States)
  2. Sandia National Lab. (SNL-CA), Livermore, CA (United States); Univ. of Central Florida, Orlando, FL (United States)
  3. Sandia National Lab. (SNL-CA), Livermore, CA (United States); Univ. of Duisburg-Essen, Duisburg (Germany)
Publication Date:
OSTI Identifier:
1188580
Report Number(s):
SAND-2014-20722J
Journal ID: ISSN 1463-9076; 553953
Grant/Contract Number:
AC04-94AL85000
Type:
Accepted Manuscript
Journal Name:
Physical Chemistry Chemical Physics. PCCP (Print)
Additional Journal Information:
Journal Name: Physical Chemistry Chemical Physics. PCCP (Print); Journal Volume: 17; Journal ID: ISSN 1463-9076
Publisher:
Royal Society of Chemistry
Research Org:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; cyclic ketones; biofuels; low-temperature oxidation; cyclopentanone; cyclohexanone; chain-termination; photoionization mass spectrometry