The Thermal Decomposition of the Benzyl Radical in a Heated Micro-Reactor. I. Experimental Findings

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, C₆H₅CH₂, as well as a set of isotopically labeled radicals: C₆H₅CD₂, C₆D₅CH₂, and C₆H₅¹³CH₂. The combination of PIMS and IR spectroscopy has been used to identify the earliest pyrolysis products from benzyl radical as: C₅H₄=C=CH₂, H atom, C₅H₄ - C CH, C₅H₅, HCCCH₂, and HC CH. Pyrolysis of the C₆H₅CD₂, C₆D₅CH₂, and C₆H₅¹³CH₂ 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: C₆H₅CH₂â‡C₇H₇. These labeling studies suggest that there must be other thermal decomposition routes for the C₆H₅CH₂ radical that differ from the fulvenallene pathway.