Reaction Mechanisms Governing the Formation of Polycyclic Aromatic Hydrocarbons in the Supercritical Pyrolysis of Toluene:  C₂₈H₁₄Isomers

Reaction pathways for the formation of C 28 H 14 polycyclic aromatic hydrocarbons (PAH) of which there are eight benzenoid isomers during the supercritical pyrolysis of toluene are described in detail. These reaction mechanisms involve the addition of benzyl, methyl, and/or phenyl radicals to smaller PAH products in three specific reactions: (A) addition of methyl and benzyl, usually to a position adjacent to a bay region; (B) addition of phenyl to a bay region; and (C) addition of two methyls to a bay region. Using these three types of reactions, we are able to explain why the five identified C 28 H 14 PAH−benzo[ a ]coronene, phenanthro[5,4,3,2- efghi ]perylene, benzo[ cd ]naphtho[3,2,1,8- pqra ]perylene, benzo[ ghi ]naphtho[8,1,2- bcd ]perylene, and benzo[ pqr ]naphtho[8,1,2- bcd ]perylene−are present in our product mixture and why bisanthene, a C 28 H 14 isomer that we know is not present from UV spectral data, is not formed. We then determine reaction pathways for the remaining two C 28 H 14 benzenoid isomers, naphthaceno[3,4,5,6,7- defghij ]naphthacene and tribenzo[ cd, ghi, lm ]perylene, to deduce that the sixth C 28 H 14 PAH detected in our product mixture by HPLC/MS is most likely tribenzo[ cd, ghi, lm ]perylene.