The C–C Bond Energy in Ethylbenzene

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Abstract
The pyrolysis of ethylbenzene in the presence of excess of toluene has been shown to be a unimolecular process, the rate-determining step being C6H5·CH2·CH3→C6H5·CH2·+CH3·.The methyl radicals were removed by a reaction with toluene, yielding CH4 and benzyl radicals, and the quantity of methane obtained was a measure of the extent of the decomposition of ethylbenzene. The energy of activation and the frequency factor were estimated experimentally at 63.2 kcal./mole and 1.0·1013 sec.−1, respectively. Taking the D(C–C)C6H5·C2H5 at 63.2 kcal./mole and using this value in conjunction with the value reported previously for D(C–H)C6H5·CH3 and the relevant thermochemical data, we calculated the D(C–H)CH4 at 102.9 kcal./mole. The results of the thermal decomposition of ethylbenzene in the absence of toluene have been investigated, but it has been found unsuitable for kinetics studies because of a complicating chain process. A short discussion on the frequency factors of these unimolecular reactions is given.