Formation and stability of gas-phase o-benzoquinone from oxidation of ortho-hydroxyphenyl: A combined neutral and distonic radical study

Prendergast, Matthew B., Kirk, Benjamin B., Savee, John D., Osborn, David L., Taatjes, Craig A., Masters, Kye-Simeon, Blanksby, Stephen J., Da Silva, Gabriel, & Trevitt, Adam J. (2016) Formation and stability of gas-phase o-benzoquinone from oxidation of ortho-hydroxyphenyl: A combined neutral and distonic radical study. Physical Chemistry Chemical Physics, 18(6), pp. 4320-4332.

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Abstract

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.

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ID Code: 96424
Item Type: Journal Article
Refereed: Yes
DOI: 10.1039/c5cp02953h
ISSN: 1463-9076
Subjects: Australian and New Zealand Standard Research Classification > CHEMICAL SCIENCE (030000) > ANALYTICAL CHEMISTRY (030100)
Divisions: Current > Schools > School of Chemistry, Physics & Mechanical Engineering
Current > Institutes > Institute for Future Environments
Current > QUT Faculties and Divisions > Science & Engineering Faculty
Funding:
Copyright Owner: Copyright 2016 Royal Society of Chemistry
Deposited On: 30 Jun 2016 02:11
Last Modified: 19 Jul 2016 04:42

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