Reaction mechanisms governing the formation of polycyclic aromatic hydrocarbons in the supercritical pyrolysis of toluene:: C28H14 isomers

Reaction pathways for the formation of C28H14 polycyclic aromatic hydrocarbons (PAH) sof which there are eight benzenoid isomers-sduring 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 C28H14 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 C28H14 isomer that we know is not present from UV spectral data, is not formed. We then determine reaction pathways for the remaining two C28H14 benzenoid isomers, naphthaceno[3,4,5,6,7-defghij] naphthacene and tribenzo[cd,ghi,lm]-perylene, to deduce that the sixth C28H14 PAH detected in our product mixture by HPLC/MS is most likely tribenzo[cd, ghi, lm] perylene.