DIRECT MASS-SPECTROMETRIC STUDY OF THE MECHANISM OF TOLUENE PYROLYSIS AT HIGH-TEMPERATURES

The detailed mechanism of the high-temperature pyrolysis of toluene has been studied over a large range of pressures and temperatures by using mass spectrometric techniques. The vapors leaving a high-temperature Knudsen cell equipped with a gas inlet line were examined by using modulated molecular beam mass spectrometric techniques. The pyrolysis products from both quartz and tungsten Knudsen cells were examined over a pressure range of 10-5 to 1 torr and temperatures up to 1800 °C. At the lower pressures, only products with molecular weights lower than C7H8 were observed, including CH3, C2H2, C3H3, C4H2, C4H3, C4H4, C6H5, C6H6, and C7H7. At higher pressure, these products undergo bimolecular processes to form heavier compounds, up to at least C20H12. To help define the reaction mechanism, the pyrolyses of C6H513CH3 and C6H6CD3 were also studied, as well as toluene in the presence of H2, C2H2, and C6H6. These studies allowed an unambiguous determination of most of the major processes occurring during toluene pyrolysis. © 1979 American Chemical Society.