Pyrolysis and isomerization of quadricyclane, norbornadiene, and toluene

Pyrolysis and isomerization of the C7H8 isomers quadricyclane, norbornadiene, cycloheptatriene, and toluene have been studied in a micro-flow tube reactor with detection/isomer identification by guided-ion beam tandem mass spectrometry. The methodology permits pyrolysis studies with product isomer identification with samples of only a few milligrams. The samples are premixed with buffer gas and then passed through a temperature-controlled flow tube reactor with millisecond residence time. The sample/pyrolysis products exiting the flow tube are ionized by methane chemical ionization (CI), and both CI mass spectra and low-energy collision-induced dissociation were used to determine the composition. For the experimental residence time, toluene and cycloheptatriene are stable over the 298-998 K temperature range. Decomposition of norbornadiene sets in at similar to 600 K. The dominant decomposition processes are acetylene elimination via a retro-Diels-Alder reaction and isomerization to toluene. Quadricyclane begins to decompose at similar to 500 K, and the dominant decomposition processes are the acetylene elimination and isomerization to toluene, with a small amount of norbornadiene production. The results are discussed in relation to previous studies at lower temperatures/longer times.