Radical Chemistry in the Thermal Decomposition of Anisole and Deuterated Anisoles: An Investigation of Aromatic Growth

Adam M. Scheer, Calvin Mukarakate, David J. Robichaud, G. Barney Ellison, Mark R. Nimlos

Research output: Contribution to journalArticlepeer-review

96 Scopus Citations

Abstract

The pyrolyses of anisole (C6H5OCH3), d3-anisole (C6H5OCD3), and d 8-anisole (C6D5OCD3) have been studied using a hyperthermal tubular reactor and photoionization reflectron time-of-flight mass spectrometer. Gas exiting the reactor is subject to an immediate supersonic expansion after a residence time of approximately 65 s. This allows the detection of highly reactive radical intermediates. Our results confirm that the first steps in the thermal decomposition of anisole are the loss of a methyl group to form phenoxy radical, followed by ejection of a CO to form cyclopentadienyl radical (c-C5H5); C 6H5OCH3 → C6H5O + CH3; C6H5O → c-C5H5 + CO. At high temperatures (Twall = 1200 °C 1300 °C) the c-C5H5 decomposes to propargyl radical (CH2CCH) and acetylene; c-C5H5 → CH2CCH + C 2H2. The formation of benzene and naphthalene is demonstrated with 1 + 1 resonance-enhanced multiphoton ionization. Propargyl radical recombination is a significant benzene formation channel. However, we show the majority of benzene is formed by a ring expansion reaction of methylcyclopentadiene (C5H5CH3) resulting from methyl radical addition to cyclopentadienyl radical; CH3 + c-C 5H5 → C5H5CH3 → C6H6 + 2H. The naphthalene is generated from cyclopentadienyl radical recombination; 2c-C5H5 → C5H5C5H5 → C10H 8 + 2H. The respective intermediate amu 79 and 129 species associated with these reactions are detected, confirming the stepwise nature of the decompositions. These reactions are verified by pyrolysis studies of cyclopentadiene (C5H6) and C5H 5CH3 obtained from rapid thermal dissociation of the respective dimer compounds, as well as pyrolysis studies of propargyl bromide (BrCH2CCH).

Original languageAmerican English
Pages (from-to)9043-9056
Number of pages14
JournalJournal of Physical Chemistry A
Volume114
Issue number34
DOIs
StatePublished - 2010

NREL Publication Number

  • NREL/JA-510-49111

Keywords

  • biomass gasification
  • pyrolysis
  • radical chemistry

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