Formation of polychlorinated naphthalenes from chlorophenols

Abstract

To test the hypothesis that polychlorinated naphthalenes (PCNs) can be formed from chlorinated phenols via cyclopentadienyl radicals in post-combustion gas containing 8% oxygen, the slow combustion of three chlorophenols (CPs) at 600 °C was studied in a laminar flow reactor. Contrary to the a priori hypothesis, different distributions of PCN isomers were produced from each CP. To explain these distributions and the observed correlation between polychlorinated dibenzofuran (PCDF) and PCN yields, a mechanism is proposed that builds on published mechanisms of PCDF formation from chlorinated phenols and naphthalene formation from dihydrofulvalene. This mechanism involves phenoxy radical coupling at unsubstituted ortho-carbon sites followed by CO elimination to produce dichloro-9,10-dihydrofulvalene intermediates. Naphthalene products are formed by loss of H and/or Cl atoms and rearrangement. Of the three chlorophenols, 3-CP produced the highest PCN and PCDF yields, as well as the greatest number of PCN and PCDF product; 2-CP produced the lowest PCN and PCDF yields. Phenol, formed by hydrodechlorination of CP, led to the formation of naphthalene and monochloronaphthalene products. This work provides a better understanding of isomer-specific PCN formation in post-combustion gas and may be developed and used as a tool for mechanism attribution in combustion systems.