Very-low-pressure pyrolysis of ethylbenzene, isopropylbenzene, and tert-butylbenzene

✍ Scribed by David A. Robaugh; Stephen E. Stein

• Publisher: John Wiley and Sons
• Year: 1981
• Tongue: English
• Weight: 754 KB
• Volume: 13
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.550130503

✦ Synopsis

The thermal unimolecular decomposition of ethylbenzene, isopropylbenzene, and tertbutylbenzene was studied using the very-low-pressure pyrolysis (VLPP) technique. Each reactant decomposed by way of 0 C-C bond homolysis, producing methyl radicals and benzyl or benzylic-type radicals. RRKM calculations show that the observed rate constants, when combined with thermochemical estimates, are consistent with the following high-pressure rate expressions: log k(sec-') = 15.3 -(72.7/8) for ethylbenzene between 1053 and 1234 K, log h(sec-') = 15.8 -(71.3/8) for isopropylbenzene between 971 and 1151 K, and log k(sec-') = 15.9 -(69.1/@ for tert-butylhenzene between 929 and 1157 K, where O(kcal/mol) = 2.303RT. Resulting activation energies combined with heat capacity and heat of formation data led to the following dissociation enthalpies and enthalpies of formation a t 298 K: DH" (@CH(CH+-CH3) = 73.8 kcal/mol, AH; (&H(CH3)) = 39.6 kcal/mol, DH" (@C(CHd-CH3) = 72.9 kcal/mol, and AH; (@C(CH&) = 32.4 kcal/mol. Derived high-pressure rate constants are in good accord with results of lower temperature toluene-and aniline-carrier experiments.