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Title: The thermal decomposition of the benzyl radical in a heated micro-reactor. II. Pyrolysis of the tropyl radical

Authors:
; ORCiD logo; ORCiD logo; ; ; ; ; ; ORCiD logo
Publication Date:
Sponsoring Org.:
USDOE
OSTI Identifier:
1260286
Grant/Contract Number:
AC02- 05CH11231; AC36-99GO10337
Resource Type:
Journal Article: Publisher's Accepted Manuscript
Journal Name:
Journal of Chemical Physics
Additional Journal Information:
Journal Volume: 145; Journal Issue: 1; Related Information: CHORUS Timestamp: 2016-12-27 20:35:35; Journal ID: ISSN 0021-9606
Publisher:
American Institute of Physics
Country of Publication:
United States
Language:
English

Citation Formats

Buckingham, Grant T., Porterfield, Jessica P., Kostko, Oleg, Troy, Tyler P., Ahmed, Musahid, Robichaud, David J., Nimlos, Mark R., Daily, John W., and Ellison, G. Barney. The thermal decomposition of the benzyl radical in a heated micro-reactor. II. Pyrolysis of the tropyl radical. United States: N. p., 2016. Web. doi:10.1063/1.4954895.
Buckingham, Grant T., Porterfield, Jessica P., Kostko, Oleg, Troy, Tyler P., Ahmed, Musahid, Robichaud, David J., Nimlos, Mark R., Daily, John W., & Ellison, G. Barney. The thermal decomposition of the benzyl radical in a heated micro-reactor. II. Pyrolysis of the tropyl radical. United States. doi:10.1063/1.4954895.
Buckingham, Grant T., Porterfield, Jessica P., Kostko, Oleg, Troy, Tyler P., Ahmed, Musahid, Robichaud, David J., Nimlos, Mark R., Daily, John W., and Ellison, G. Barney. 2016. "The thermal decomposition of the benzyl radical in a heated micro-reactor. II. Pyrolysis of the tropyl radical". United States. doi:10.1063/1.4954895.
@article{osti_1260286,
title = {The thermal decomposition of the benzyl radical in a heated micro-reactor. II. Pyrolysis of the tropyl radical},
author = {Buckingham, Grant T. and Porterfield, Jessica P. and Kostko, Oleg and Troy, Tyler P. and Ahmed, Musahid and Robichaud, David J. and Nimlos, Mark R. and Daily, John W. and Ellison, G. Barney},
abstractNote = {},
doi = {10.1063/1.4954895},
journal = {Journal of Chemical Physics},
number = 1,
volume = 145,
place = {United States},
year = 2016,
month = 7
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1063/1.4954895

Citation Metrics:
Cited by: 1work
Citation information provided by
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  • Cycloheptatrienyl (tropyl) radical, C7H7, was cleanly produced in the gas-phase, entrained in He or Ne carrier gas, and subjected to a set of flash-pyrolysis micro-reactors. The pyrolysis products resulting from C7H7 were detected and identified by vacuum ultraviolet photoionization mass spectrometry. Complementary product identification was provided by infrared absorption spectroscopy. Pyrolysis pressures in the micro-reactor were roughly 200 Torr and residence times were approximately 100 us. Thermal cracking of tropyl radical begins at 1100 K and the products from pyrolysis of C7H7 are only acetylene and cyclopentadienyl radicals. Tropyl radicals do not isomerize to benzyl radicals at reactor temperatures upmore » to 1600 K. Heating samples of either cycloheptatriene or norbornadiene never produced tropyl (C7H7) radicals but rather only benzyl (C6H5CH2). The thermal decomposition of benzyl radicals has been reconsidered without participation of tropyl radicals. There are at least three distinct pathways for pyrolysis of benzyl radical: the Benson fragmentation, the methyl-phenyl radical, and the bridgehead norbornadienyl radical. These three pathways account for the majority of the products detected following pyrolysis of all of the isotopomers: C6H5CH2, C6H5CD2, C6D5CH2, and C6H5 13CH2. Analysis of the temperature dependence for the pyrolysis of the isotopic species (C6H5CD2, C6D5CH2, and C6H5 13CH2) suggests the Benson fragmentation and the norbornadienyl pathways open at reactor temperatures of 1300 K while the methyl-phenyl radical channel becomes active at slightly higher temperatures (1500 K).« less
  • Cited by 7
  • The pyrolysis of the benzyl radical has been studied in a set of heated micro-reactors. A combination of photoionization mass spectrometry (PIMS) and matrix isolation infrared (IR) spectroscopy has been used to identify the decomposition products. Both benzyl bromide and ethyl benzene have been used as precursors of the parent species, C{sub 6}H{sub 5}CH{sub 2}, as well as a set of isotopically labeled radicals: C{sub 6}H{sub 5}CD{sub 2}, C{sub 6}D{sub 5}CH{sub 2}, and C{sub 6}H{sub 5}{sup 13}CH{sub 2}. The combination of PIMS and IR spectroscopy has been used to identify the earliest pyrolysis products from benzyl radical as: C{sub 5}H{submore » 4}=C=CH{sub 2}, H atom, C{sub 5}H{sub 4}—C ≡ CH, C{sub 5}H{sub 5}, HCCCH{sub 2}, and HC ≡ CH. Pyrolysis of the C{sub 6}H{sub 5}CD{sub 2}, C{sub 6}D{sub 5}CH{sub 2}, and C{sub 6}H{sub 5}{sup 13}CH{sub 2} benzyl radicals produces a set of methyl radicals, cyclopentadienyl radicals, and benzynes that are not predicted by a fulvenallene pathway. Explicit PIMS searches for the cycloheptatrienyl radical were unsuccessful, there is no evidence for the isomerization of benzyl and cycloheptatrienyl radicals: C{sub 6}H{sub 5}CH{sub 2}⇋C{sub 7}H{sub 7}. These labeling studies suggest that there must be other thermal decomposition routes for the C{sub 6}H{sub 5}CH{sub 2} radical that differ from the fulvenallene pathway.« less
  • The thermal decomposition of benzyl iodide into benzyl radicals + I was studied in shock waves by UV absorption spectroscopy. Rate constants k/sub 1/ = 10/sup 14.78/ exp(/minus/181 kJ mol/sup /minus/1//RT) s/sup /minus/1/ for the dissociation, and k/sub 2/ = 10/sup 13.70/ cm/sup 3/ mol/sup /minus/1/ s/sup /minus/1/ for the reverse recombination of benzyl radicals and iodine atoms, were derived over the range 750 less than or equal to T less than or equal to 950 K. For the subsequent recombination of the formed benzyl radicals to dibenzyl, a rate constant k/sub 7/ = 10/sup 12.60/(T/1000 K)/sup 0.4/ cm/sup 3/more » mol/sup /minus/1/ s/sup /minus/1/ was obtained together with a dibenzyl dissociation rate constant of k/sub 8/ = 10/sup 14.9/ exp(-250 kJ mol/sup /minus/1//RT) s/sup /minus/1/ (temperature range 900 less than or equal to T less than or equal to 1500 K). The UV absorption spectra and dissociation rate constants k/sub 11/ of benzyl radicals were then studied from 1250 up to 1900 K. k/sub 11/ is represented as the sum k/sub 9/ + k/sub 10/ with k/sub 9/ = 10/sup 10.22/exp(-187 kJ mol/sup /minus/1//RT) s/sup /minus/1/ and k/sub 10/ = 10/sup 15.30/ exp(-349.6 kJ mol/sup /minus/1//RT) s/sup /minus/1/. The spectroscopic and kinetic properties at high temperatures of benzyl radicals derived from several different precursor molecules agree.« less
  • Pyrolysis studies of silica-immobilized benzyl phenyl ether ({approx}PhOCH{sub 2}Ph or {approx}BPE), a model for related ether structures in fuel resources, have been conducted at 275--325 C to examine the impact of restricted mass transport on the pyrolysis mechanism compared with previous studies in fluid phases. Significant rearrangement chemistry is observed for {approx}BPE occurring through two competitive free-radical pathways that are both promoted by the diffusional constraints. One path involves recombination of incipient benzyl and surface-bound phenoxy radicals to form benzylphenol isomers, 10. The second, previously unreported rearrangement path for {approx}BPE involves a 1,2-phenyl shift in an intermediate radical, {approx}PhOCH{center_dot}Ph, leadingmore » to formation of benzhydrol (8) and benzophenone (9) as principal products. The rearrangement products 8--10 typically account for ca. 50% of the pyrolysis products. However, the path selectivity is a sensitive function of {approx}BPE surface coverage and the presence of spacer molecules that either facilitate or hinder hydrogen atom transfer steps on the surface.« less