Hydroxyl radical formation in the gas phase oxidation of distonic 2-methylphenyl radical cations

Prendergast, M. B., Cooper, P. A., Kirk, B. B., da Silva, G., Blanksby, S. J., & Trevitt, A. J. (2013) Hydroxyl radical formation in the gas phase oxidation of distonic 2-methylphenyl radical cations. Physical Chemistry Chemical Physics, 15(47), pp. 20577-20584.

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The reactions of distonic 4-(N, N, N-trimethylammonium)-2-methylphenyl and 5-(N, N, N-trimethylammonium)-2-methylphenyl radical cations (m/z 149) with O-2 are studied in the gas phase using ion-trap mass spectrometry. Photodissociation (PD) of halogenated precursors gives rise to the target distonic charge-tagged methylphenyl radical whereas collision-induced dissociation (CID) is found to produce unreactive radical ions. The PD generated distonic radicals, however, react rapidly with O-2 to form [M + O2](center dot+) and [M + O-2 - OH](center dot+) ions, detected at m/z 181 and m/z 164, respectively. Quantum chemical calculations using G3SX(MP3) and M06-2X theories are deployed to examine key decomposition pathways of the 5-(N, N, N-trimethylammonium)-2-methylphenylperoxyl radical and rationalise the observed product ions. The prevailing product mechanism involves a 1,5- H shift in the peroxyl radical forming a QOOH-type intermediate that subsequently eliminates (OH)-O-center dot to yield charge-tagged 2-quinone methide. Our study suggests that the analogous process should occur for the neutral methylphenyl + O-2 reaction, thus serving as a plausible source of (OH)-O-center dot radicals in combustion environments.

Grants: ARC/DP0986738, ARC/DP130100862

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ID Code: 68932
Item Type: Journal Article
Refereed: Yes
Keywords: trap mass-spectrometer, quadrupole ion-trap, charged phenyl radicals, o-quinone methide, plus o-2 reaction, thermal-decomposition, unimolecular decomposition, phenylperoxyl radicals, molecular-oxygen, atom abstraction, ARC
DOI: 10.1039/c3cp53690d
ISSN: 1463-9076
Subjects: Australian and New Zealand Standard Research Classification > CHEMICAL SCIENCE (030000)
Divisions: Current > QUT Faculties and Divisions > Science & Engineering Faculty
Copyright Owner: Royal Society of Chemistry
Deposited On: 20 Mar 2014 03:57
Last Modified: 24 Jan 2016 09:20

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