High temperature synthesis of aromatic hydrocarbons



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Aromatic hydrocarbons have been synthesized in a flow system by passing methane or isoprene through silica gel at 1000[degrees]C or 300[degrees]C to lOOO[degrees]C with 100[degrees]C intervals. Yields and structures of the products are dependent on the pyrolysis temperature. At 1000[degrees]C methane and isoprene would give the same products' pattern. The major products of 1 to 4 rings are benzene, toluene, naphthalene, acenaphthylene, phenanthrene, fluoranthene, and pyrene. At high temperatures, unsubstituted aromatic hydrocarbons are the major products, and C2 units are the important intermediates for the mechanism. As determined by combined gas chromatography-mass spectrometry, 49 compounds synthesized of less than 5 rings are found in the product of pyrolysis of isoprene at 700[degrees]C. The ultra violet spectrophotometry was used to detect the high molecular weight aromatic hydrocarbons with 4 to 7 rings. Fifteen compounds, including the most carcinogenic polynuclear hydrocarbon, 3,4-benzopyrene, are found by this method. A brief discussion of the possible mechanism of synthesis and the significance of these results to organic cosmochemistry is presented.