Correlation between structure and reactivity of diarylmethanes as coal-related model substances

Abstract

The kinetics of diarylmethanes thermolysis has been studied in excess tetralin and under hydrogen pressure. It has been shown that the logarithms of thermolysis rate constants for the most diarylmethanes are proportional to the sums of the reactivity indices of carbon atoms connected with the methylene group, i.e. log k = f ( ϵN t ). This conformity accords with the mechanism of ipso-attack as the limiting stage of the whole process. But two diarylmethanes do not submit to this conformity: 9-benzylanthracene reacts with a rate ten times greater than the predicted one and diphenylmethane transforms with much lesser rate as compared to the predicted one. These deviations have been explained. 9-Benzylanthracene is easily hydrogenated before destruction, i.e. in this case a much weaker bond, C alk-C alk, than the C ar-C alk bond is ruptured. Diphenylmethane is disproportionated into diphenylmethyl and benzylcyclohexadienyl radicals. The former is less active and transforms relatively slowly into fluorene, and the latter is the more active but it undergoes exchange in the presence of tetralin giving back diphenylmethane and cyclohexadienylic radical of tetralin. This is the reason for the relative inactivity of diphenylmethane.