Chemistry of fullerenes C60 and C70 formation in flames

Abstract

A kinetic mechanism is constructed for the formation of fullerenes C[sub 60] and C[sub 70] in flames, based on types of reactions used in describing growth of polycyclic aromatic hydrocarbons (PAH) and including additional chemical processes needed to describe evolution of the unique structural features of fullerenes. The mechanism consists of types of reactions, each characterized by an approximate rate coefficient, including processes for ring formation (via H atom abstraction, C[sub 2]H[sub 2] addition, and cyclization leading to ring closing), reactive coagulation of aromatic molecules, and cage closing via H[sub 2] elimination and ring closing but also allowing for additional processes such as intramolecular rearrangements. Curved PAH, including benzo[ghi]fluoranthene (C[sub 18]H[sub 10]) and dibenzo-[ghi,mno]fluoranthene (corannulene, C[sub 20]H[sub 10]), are likely fullerene precursors. Corannulene is considered a key immediate in the fullerene formation mechanism. Although alternatives to corannulene as an intermediate are mentioned, the proposed mechanism is based on corannulene and other related PAH of C[sub 50] symmetry. Trivial nomenclature for the C[sub 50] intermediates is also introduced. Preliminary kinetic testing of the mechanism, using approximate rate coefficients based on analogous flat PAH reactions, shows the mechanism to be plausible. 84 refs., 12 figs., 4 tabs.