Formation and stability of gas-phase o-benzoquinone from oxidation of ortho-hydroxyphenyl: a combined neutral and distonic radical study.
Gas-phase product detection studies of o-hydroxyphenyl radical and O2 are reported at 373, 500, and 600 K, at 4 Torr (533.3 Pa), using VUV time-resolved synchrotron photoionisation mass spectrometry. The dominant products are assigned as o-benzoquinone (C6H4O2, m/z 108) and cyclopentadienone (C5H4O, m/z 80). It is concluded that cyclopentadienone forms as a secondary product from prompt decomposition of o-benzoquinone (and dissociative ionization of o-benzoquinone may contribute to the m/z 80 signal at photon energies ≳9.8 eV). Ion-trap reactions of the distonic o-hydroxyphenyl analogue, the 5-ammonium-2-hydroxyphenyl radical cation, with O2 are also reported and concur with the assignment of o-benzoquinone as the dominant product. The ion-trap study also provides support for a mechanism where cyclopentadienone is produced by decarbonylation of o-benzoquinone. Kinetic studies compare oxidation of the ammonium-tagged o-hydroxyphenyl and o-methylphenyl radical cations along with trimethylammonium-tagged analogues. Reaction efficiencies are found to be ca. 5% for both charge-tagged o-hydroxyphenyl and o-methylphenyl radicals irrespective of the charged substituent. G3X-K quantum chemical calculations are deployed to rationalise experimental results for o-hydroxyphenyl + O2 and its charge-tagged counterpart. The prevailing reaction mechanism, after O2 addition, involves a facile 1,5-H shift in the peroxyl radical and subsequent elimination of OH to yield o-benzoquinone that is reminiscent of the Waddington mechanism for β-hydroxyperoxyl radicals. These results suggest o-hydroxyphenyl + O2 and decarbonylation of o-benzoquinone serve as plausible OH and CO sources in combustion.
School of Chemistry, University of Wollongong, Wollongong, NSW 2522, Australia. adamt@uow.edu.au.
Matthew B
MB
Prendergast
Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
Benjamin B
BB
Kirk
Combustion Research Facility, Sandia National Laboratories, Livermore, CA 94551-0969, USA.
John D
JD
Savee
Combustion Research Facility, Sandia National Laboratories, Livermore, CA 94551-0969, USA.
David L
DL
Osborn
Combustion Research Facility, Sandia National Laboratories, Livermore, CA 94551-0969, USA.
Craig A
CA
Taatjes
School of Chemistry, Physics and Mechanical Engineering, Faculty of Science and Engineering, Queensland University of Technology, Brisbane, QLD 4001, Australia.
Kye-Simeon
KS
Masters
Central Analytical Research Facility, Queensland University of Technology, Brisbane, QLD 4001, Australia.
Stephen J
SJ
Blanksby
Department of Chemical and Biomolecular Engineering, The University of Melbourne, Melbourne, VIC 3010, Australia.
Gabriel
G
da Silva
School of Chemistry, University of Wollongong, Wollongong, NSW 2522, Australia. adamt@uow.edu.au.
Adam J
AJ
Trevitt