The gas-phase methylation of benzene and toluene

Zhe Chen Wang, Ditte L. Thomsen, Edwin L. Motell, Marin S Robinson, Rustam Garrey, Veronica M. Bierbaum, Charles H. DePuy

Research output: Contribution to journalArticle

2 Citations (Scopus)

Abstract

The reactions of the methyl cation with benzene and toluene in the gas phase have been examined using the flowing afterglow-selected ion flow-drift tube technique. With benzene four product ions are formed, C6H6 + by electron transfer, C6H5 + by addition and loss of CH4, C7H7 + by addition and loss of H2, and an adduct C7H9 +. Deuterium and carbon-13 labeling experiments were carried out to provide mechanistic insights. In agreement with earlier work, deuterium labeling (CD3 + with C6H6 or CH3 + with C6D6) shows that partial H/D scrambling between the methyl group and the ring occurs during the formation of C6H5 + and C7H7 +. However, in contrast to earlier work, no carbon-13 scrambling was observed between the methyl and ring carbons, thus ruling out a ring expansion and contraction mechanism to account for the H/D scrambling. Nor did we find H/D scrambling in the electron transfer product ion, C6H6 +. When collision-induced dissociation (CID) was carried out on the adduct ion, extensive H/D and carbon-13 scrambling was found, indicating that at least some ring expansion occurs during its formation. Reaction of C6H5 + with methane at room temperature exclusively forms the adduct ion, but addition followed by loss of CH4 and addition with loss of H2 were also observed when the ion was given kinetic energy in a drift field. Mechanisms are proposed which account for our results, and these are supported by ab initio calculations. Similar studies were carried out with toluene as the neutral reagent. Besides the four analogous product ions, we found hydride transfer from the methyl group of toluene to be a major reaction channel and addition with loss of ethylene to be a minor channel.

Original languageEnglish (US)
JournalInternational Journal of Mass Spectrometry
DOIs
StateAccepted/In press - Feb 6 2017

Fingerprint

methylation
Methylation
Toluene
Benzene
toluene
Gases
benzene
Ions
vapor phases
carbon 13
Carbon
ions
adducts
Deuterium
rings
Labeling
marking
deuterium
electron transfer
products

Keywords

  • Flowing afterglow-selected ion flow tube
  • Friedel-Crafts-alkylation
  • Gas-phase ion chemistry
  • H/D scrambling
  • Isotopic labeling
  • Mass spectrometry
  • Molecular hydrogen loss
  • Wheland-intermediate

ASJC Scopus subject areas

  • Instrumentation
  • Condensed Matter Physics
  • Spectroscopy
  • Physical and Theoretical Chemistry

Cite this

Wang, Z. C., Thomsen, D. L., Motell, E. L., Robinson, M. S., Garrey, R., Bierbaum, V. M., & DePuy, C. H. (Accepted/In press). The gas-phase methylation of benzene and toluene. International Journal of Mass Spectrometry. https://doi.org/10.1016/j.ijms.2017.03.009

The gas-phase methylation of benzene and toluene. / Wang, Zhe Chen; Thomsen, Ditte L.; Motell, Edwin L.; Robinson, Marin S; Garrey, Rustam; Bierbaum, Veronica M.; DePuy, Charles H.

In: International Journal of Mass Spectrometry, 06.02.2017.

Research output: Contribution to journalArticle

Wang, Zhe Chen ; Thomsen, Ditte L. ; Motell, Edwin L. ; Robinson, Marin S ; Garrey, Rustam ; Bierbaum, Veronica M. ; DePuy, Charles H. / The gas-phase methylation of benzene and toluene. In: International Journal of Mass Spectrometry. 2017.
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AU - Thomsen, Ditte L.

AU - Motell, Edwin L.

AU - Robinson, Marin S

AU - Garrey, Rustam

AU - Bierbaum, Veronica M.

AU - DePuy, Charles H.

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KW - Wheland-intermediate

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