Pyrocondensation of Anthracene

Article abstract of DOI:10.1021/jo00384a037

The predominant initial products in the thermal chemistry of anthracene are 2,9'-bianthracenyl and 9,10-dihydroanthracene.Over the range 350-500 deg C, in the gas and liquid phase, this reaction follows second-order kinetics with k/M^-1 s^-1 = 10^7.37+/-0.27 exp<-22520+/-420/T>.The only other major products is 1,9'-bianthracenyl, which at low extents of reaction is formed at a rate one-seventh that of 2,9'-bianthracenyl.Anthracene selectively forms biaryls with the following compounds (relative rate constants for forming the major cross-biaryls are in parentheses): naphthalene (0.5) phenanthrene (0.2), biphenyl(0.2), diphenyl ether (0.2).A kinetic analysis of results leads us to propose that the initial step in these reactions is the reversible formation of a diradical via coupling of two ground-state molecules.This is followed by a rate-limiting, intramolecular H-transfer step resulting in a dihydrobiaryl molecule, which then rapidly loses two hydrogen atoms, probably by free radical reactions, to form the major biaryl products.Minor biaryl products are formed in a less selective manner in a reaction catalyzed by 9,10-dihydroanthracene.Aryl radicals are likely intermediates in these reactions.