REACTIONS OF THERMALLY GENERATED 1-ADAMANTYL AND DI(1-ADAMANTYL)KETYL RADICALS IN TOLUENE

Thermolysis of tri(l-adamantyl)methanol in toluene at 145–185 °C gives bibenzyl, di(l-adamantyl) ketone, di(l-adamantyl)methanol and a cross-product, l,l-di(l-adamantyl)-2-phenylethanol, in yields which depend on the temperature and the isotopic composition of the solvent. In the presence of benzophenone the intermediate di(l-adamantyl)ketyl radical transfers hydrogen, giving ketone and the hydroxybenzhydryl radical, the cross-product then being 1,1,2-triphenylethanol. The cage effect (0.38-0.415) has been determined by studying thermolysis in deuterium-labeled toluene. In normal toluene almost all the secondary alcohol is formed from Ad2C•OH by hydrogen abstraction from the solvent, whereas in deuteriated toluene 22-32% results from self-disproportionation of ketyl radicals, showing that there is a substantial kinetic isotope effect on hydrogen abstraction. Kinetic modeling of the reaction by means of a rapid, iterative procedure based on the steady-state approximation suggests values in the range 6.0-7.4, decreasing as the temperature rises. © 1990, American Chemical Society. All rights reserved.