Identification of Methylene-Bridged Polycyclic Aromatic Hydrocarbon Products of Catechol Pyrolysis

Abstract

As methylene-bridged polycyclic aromatic hydrocarbons (PAH) are known for their carcinogenicity and occurrence in solid-fuel byproducts and environmental samples, we have employed high-pressure liquid chromatography with diode-array ultraviolet- visible absorbance and mass spectrometric detection (HPLC/UV/MS) to search for methylene-bridged PAH among the products of the laboratory-scale pyrolysis of cate- chol, a model fuel representing aromatic moieties in coal, tobacco, and plant-based biomass fuels. Utilizing two different octadecylsilica columns and five different mobile- phase separation methods, the HPLC/UV/MS analyses have led to the unequivocal identification of six methylene-bridged PAH among the products of catechol pyrolysis at 1000°C and 0.3 s in a laminar-flow reactor: the C15H10 4H-cyclopenta- [def]phenanthrene, the C19H12 11H-benz[bc]aceanthrylene and 4H-cyclopenta[def]- chrysene, the C21H12 11H-indeno[2,1,7-cde]pyrene and 4H-benzo[def]cyclopenta[mno]- chrysene, and the C23H12 1H-benzo[ghi]cyclopenta[pqr]perylene. None of these six methylene-bridged PAH have ever before been identified as pyrolysis products of catechol or of any other pure-component fuel. The mass and UV spectra of two additional catechol pyrolysis product components have been examined in light of the finding that the UV spectra of methylene-bridged PAH generally resemble those of their respective parent benzenoid PAH (but with a 5- to 12-nm bathochromic shift in the p band)—resulting in the identification of a methylene-bridged naphtho[2,1-a]pyrene and the tentative identification of a methylene-bridged naphtho[2,3-a]pyrene, two previously unrecognized C25H14 PAH that would be expected to exhibit significant mutagenic and/or carcinogenic behavior.