The Identification of New Ethynyl-Substituted and Cyclopenta-Fused Polycyclic Aromatic Hydrocarbons in the Products of Anthracene Pyrolysis

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Abstract
The recent synthesis of new reference standards of polycyclic aromatic hydrocarbons (PAH) has enabled us to identify six new PAH species among the products of anthracene, pyrolyzed in argon at temperatures of 1300 to 1500 K. The anthracene product samples are analyzed by high performance liquid chromatography (HPLC) with diode-array ultraviolet-visible (UV) detection, and the identifications are made by matching each product component's HPLC elution time and UV absorption spectrum with those of the corresponding reference standard. The newly identified PAH products include 1-ethynylacenaphthylene (C14H8) as well as five cyclopenta-fused PAH (CP-PAH): cyclopenta[cd]fluoranthene (C18H10); dicyclopenta[cd, mn]pyrene, dicyclo-penta[cd,fg]pyrene, dicyclopenta[cd,jk]pyrene (C20H10); and benzo[ghi]cyclopenta[cd]-perylene (C24H12). Undetectable at temperatures < 1300 K, the yields of the newly identified CP-PAH rise quickly with temperature above 1350 K, levelling off somewhat at temperatures approaching 1500 K. The five new CP-PAH, along with five previously identified CP-PAH, together account for approximately a quarter, by number, of the anthracene product PAH identified and quantified to date. At the highest temperatures, the CP-PAH as a whole account for almost half of the mass of the “thermally produced” P \H, the dominant PAH under the conditions at which soot is the major product. The results show some consistency with a CP-PAH formation mechanism involving acetylene atldition to aryl radicals, followed by cyclization of the resulting ethynyl-PAH. Further research is needed, however, to better elucidate the governing reaction mechanisms.

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