THE (C-H) BOND DISSOCIATION ENERGY IN THE METHYL GROUP OF TOLUENE

A kinetic study of the pyrolysis of toluene by a flow technique has been made, and assuming Szwarc's mechanism, two activation energies (78.3 and 84 kcal/ mole depending on the temperature range used) have been derived for the dissociation of the (C-H) bond in the methyl group of toluene. The lower value agrees quite well with Szwarc's, and the higher value turns out to be approxo- mately the average of 77 5 and 89.9. The results of this research-suggest 84 kcal/mole as the upper limit for the activation energy. The ultraviolet spectra of the solid decomposition product indicated that the solid was not pure dibenzyl but probably contained small amounts of a compound possessing a diphenyl nucleus. The rate of formation of hydrogen and methane was found to be inhibited by small amounts of air, and the percentage of hydrogen was found to increase slightly with temperature. A detailed description of the apparatus and its operation is given. The concept of group potential has been introduced to predict bond dissociation energies of carbon-hetero atom and carboncarbon bonds. (auth)