Thermal cleavage of the one-atom aryl-hydroaryl bridge in 2-(1-naphthylmethyl)-3,4-dihydronaphthalene

2-(1-Naphthylmethyl)-3,4-dihydronaphthalene (NMDN) was pyrolyzed neat at temperatures between 300 and 385°C for batch holding times between 20 and 360 min. The products formed in the highest molar yields at moderate conversions are 2-(1-naphthalenylmethyl)naphthalene (dinaphthylmethane), 1-methylnaphthalene, 1,2-dihydronaphthalene (dialin), and 2-(1-naphthylmethyl)tetrahydronaphthalene (naphthyltetralylmethane). At higher conversions, 1,2,3,4-tetrahydronaphthalene (tetralin) and naphthalene appeared as important products. The temporal variations of the products' molar yields indicated that all of the products above, save tetralin, were primary products. These assignments led to a NMDN reaction network that comprises four parallel, stoichiometrically balanced, primary pathways. These paths lead to dinaphthylmethane plus H₂, to dialin plus 1-methylnaphthalene plus dinaphthylmethane, to naphthyltetralylmethane plus dinaphthylmethane, and to naphthalene plus 2-methyldialin plus dinaphthylmethane. The kinetics of NMDN disappearance at 325°C were consistent with a second-order rate law. The Arrhenius parameters for the second-order rate constant, determined at temperatures between 300 and 385°C, are log A (L/(mol s)) = 8.8 ± 1.1 and E = 36.4 ± 3.2 kcal/mol. The observed reaction products and kinetics are consistent with a free-radical mechanism. Molecular disproportionation generates reactive free-radical intermediates, which can then participate in chain reactions to form the observed products. The observed kinetics are consistent with two different assumptions about the rates of different elementary steps in the mechanism. One is that the molecular disproportionation step is rate controlling and the other is that the chain reactions possess a long kinetic chain length. An examination of the kinetics of NMDN disappearance, alone, is not sufficient to discriminate between these two mutually exclusive possibilities.