Unimolecular Thermal Decomposition of Dimethoxybenzenes

David J. Robichaud, Adam M. Scheer, Calvin Mukarakate, Thomas K. Ormond, Grant T. Buckingham, G. Barney Ellison, Mark R. Nimlos

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30 Scopus Citations

Abstract

The unimolecular thermal decomposition mechanisms of o-, m-, and p-dimethoxybenzene (CH3O-C6H4-OCH3) have been studied using a high temperature, microtubular (μtubular) SiC reactor with a residence time of 100 μs. Product detection was carried out using single photon ionization (SPI, 10.487 eV) and resonance enhanced multiphoton ionization (REMPI) time-of-flight mass spectrometry and matrix infrared absorption spectroscopy from 400 K to 1600 K. The initial pyrolytic step for each isomer is methoxy bond homolysis to eliminate methyl radical. Subsequent thermolysis is unique for each isomer. In the case of o-CH 3O-C6H4-OCH3, intramolecular H-transfer dominates leading to the formation of o-hydroxybenzaldehyde (o-HO-C6H4-CHO) and phenol (C6H5OH). Para-CH3O-C6H4-OCH3 immediately breaks the second methoxy bond to form p-benzoquinone, which decomposes further to cyclopentadienone (C5H4=O). Finally, the m-CH 3O-C6H4-OCH3 isomer will predominantly follow a ring-reduction/CO-elimination mechanism to form C 5H4=O. Electronic structure calculations and transition state theory are used to confirm mechanisms and comment on kinetics. Implications for lignin pyrolysis are discussed.

Original languageAmerican English
Article number234302
Number of pages14
JournalThe Journal of Chemical Physics
Volume140
Issue number23
DOIs
StatePublished - 21 Jun 2014

NREL Publication Number

  • NREL/JA-5100-62380

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