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.

Key Words:

• catechol
• high-pressure liquid chromatography
• methylene-bridged polycyclic aromatic hydrocarbons
• PAH
• product identification
• pyrolysis
• UV spectra

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Acknowledgments

The authors gratefully acknowledge the following for reference standards and/or UV spectra of PAH: Dr. Arthur Lafleur and Ms. Elaine Plummer, of the Massachusetts Institute of Technology; Dr. Dianne Poster, of the National Institute of Standards and Technology; and Dr. Albrecht Seidel, of Biochemisches Institut für Umweltcarcinogene. Dr. Jorge Oña, Dr. Xia Zhang, and Dr. Franz Ehrenhauser are also gratefully acknowledged for technical contributions.