title: Unimolecular thermal decomposition of dimethoxybenzenes.
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-CH3O-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-CH3O-C6H4-OCH3 isomer will predominantly follow a ring-reduction/CO-elimination mechanism to form C5H4=O. Electronic structure calculations and transition state theory are used to confirm mechanisms and comment on kinetics. Implications for lignin pyrolysis are discussed.
authors: National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, USA.
authors: David J
authors: DJ
authors: Robichaud
authors: National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, USA.
authors: Adam M
authors: AM
authors: Scheer
authors: National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, USA.
authors: Calvin
authors: C
authors: Mukarakate
authors: National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, USA.
authors: Thomas K
authors: TK
authors: Ormond
authors: National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, USA.
authors: Grant T
authors: GT
authors: Buckingham
authors: Department of Chemistry and Biochemistry, University of Colorado-Boulder, Boulder, Colorado 80309-0215, USA.
authors: G Barney
authors: GB
authors: Ellison
authors: National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, USA.
authors: Mark R
authors: MR
authors: Nimlos
mesh_terms: D001547:Benzaldehydes / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry*; D007700:Kinetics; D008031:Lignin / Q000737:chemistry; D013058:Mass Spectrometry; D015394:Molecular Structure; D010636:Phenols / Q000737:chemistry
chemical_list: D001547:Benzaldehydes; D010636:Phenols; C538871:o-hydroxybenzaldehyde; D006859:Hydrogen; D008031:Lignin