Thermal Decomposition Mechanisms of the Methoxyphenols: Formation of Phenol, Cyclopentadienone, Vinylacetylene, and Acetylene

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

Research output: Contribution to journalArticlepeer-review

82 Scopus Citations

Abstract

The pyrolyses of the guaiacols or methoxyphenols (o-, m-, and p-HOC 6H 4OCH 3) have been studied using a heated SiC microtubular (μ-tubular) reactor. The decomposition products are detected by both photoionization time-of-flight mass spectroscopy (PIMS) and matrix isolation infrared spectroscopy (IR). Gas exiting the heated SiC μ-tubular reactor is subject to a free expansion after a residence time of approximately 50 - 100 μs. The PIMS reveals that, for all three guaiacols, the initial decomposition step is loss of methyl radical: HOC 6H 4OCH 3 → HOC 6H 4O + CH 3. Decarbonylation of the HOC 6H 4O radical produces the hydroxycyclopentadienyl radical, C 5H 4OH. As the temperature of the μ-tubular reactor is raised to 1275 K, the C 5H 4OH radical loses a H atom to produce cyclopentadienone, C 5H 4≥O. Loss of CO from cyclopentadienone leads to the final products, acetylene and vinylacetylene: C 5H 4≥O → [CO + 2 HC≡CH] or [CO + HC≡C - CH≥CH 2]. The formation of C 5H 4≥O, HCCH, and CH 2CHCCH is confirmed with IR spectroscopy. In separate studies of the (1 + 1) resonance-enhanced multiphoton ionization (REMPI) spectra, we observe the presence of C 6H 5OH in the molecular beam: C 6H 5OH + λ 275.1nm → [C 6H 5OH A] + λ 275.1nm → C 6H 5OH +. From the REMPI and PIMS signals and previous work on methoxybenzene, we suggest that phenol results from a radical/radical reaction: CH 3 + C 5H 4OH → [CH 3 - C 5H 4OH]* → C 6H 5OH + 2H.

Original languageAmerican English
Pages (from-to)13381-13389
Number of pages9
JournalJournal of Physical Chemistry A
Volume115
Issue number46
DOIs
StatePublished - 2011

NREL Publication Number

  • NREL/JA-5100-53724

Keywords

  • combustion
  • gas phase
  • gasification
  • thermochemical decomposition

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