Kinetics and mechanism of the cyclisation reaction of ortho-methylbiphenyls

Abstract

ortho Substituted methylbiphenyls undergo cyclisation reactions to give fluorenes when heated under non-catalytic conditions in the laboratory at temperatures in the range 420–480°C. Experiments have been carried out to measure the reaction rates of dimethylbiphenyls, trimethylbiphenyls and compounds in which the benzylic hydrogens were replaced with deuterium. The results obtained are consistent with a reaction mechanism involving thermally induced, uncatalysed, homolytic cleavage of the benzylic C-H bond as the rate determining step. A statistical treatment has been carried out to assess factors which control the precision of values of E and Z, the activation energy and frequency factor, obtained from such laboratory heating studies. Experiments were then designed to provide values for these kinetic parameters which would be sufficiently accurate to be useful in reconstruction of the palaeotemperatures and geothermal histories of sediments.