Biarene Formation during Pyrolysis of a Mixture of Anthracene and Naphthalene

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Abstract
The relative abundances of the six isomeric naphthyl-anthracenes, six isomeric bianthracenes and three isomeric binaphthalenes, as well as of the total secondary products have been measured for the pyrolysis of a 1 : 1 mole ratio mixture of anthracene and naphthalene. A residence time of 2 seconds and a temperature range of 1180−1500 K is used, and similar pyrolysis experiments are also performed using pure anthracene and pure naphthalene as fuels. Several polyarene products consisting of naphthyl and anthryl components have also been observed in chains up to at least 6 units long. The suggestion is made that thermodynamic equilibrium is not the governing factor in polyarene formation (a notion previously presented by Mulholland et al., 1993) as evidenced by the following observations. First, the relative abundances of the primary biarene products are found to conform roughly to those that can be calculated using simple kineticlstatistical and steric hindrance considerations. Second, the total abundance of the 6 naphthyl-anthracenes is calculated, on a mole basis, to be double that of both the total bianthracene abundance and the total binaphthalene abundance. In addition, the binaphthalene concentrations peak at a slightly higher temperature than those of the naphthyl-anthracenes, which in turn peak at a slightly higher temperature than those of the bianthracenes. These observations support the use of a kinetic model for biarene formation based solely on probabilities of collision and steric hindrance considerations, with anthryl radicals forming at a lower temperature than the naphthyl radicals.