Competitive unimolecular reactions at low pressures. The pyrolysis of cyclobutyl chloride

✍ Scribed by Keith D. King; Brendan J. Gaynor; Robert G. Gilbert

• Publisher: John Wiley and Sons
• Year: 1979
• Tongue: English
• Weight: 504 KB
• Volume: 11
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.550110103

✦ Synopsis

The thermal decomposition of cyclobutyl chloride has been investigated over the temperature range of 892-1150 K using the technique of very low-pressure pyrolysis (VLPP). The reaction proceeds via two competitive unimolecular channels, one to yield ethylene and vinyl chloride and the other to yield 1,3-butadiene and hydrogen chloride, with the latter being the major reaction under the experimental conditions. With the usual assumption that gas-wall collisions are "strong," RRKM calculations, generalized to take into account two competing pathways, show that the experimental unimolecular rate constants are consistent with the high-pressure Arrhenius parameters given by log kl(sec-') = (14.8 f 0.3) -(61.1 1.0)/8 for vinyl chloride formation and log kz(sec-1) = (13.6 f 0.3) -(55.7 f 1.0)/8 for 1,3-butadiene formation, where 8 = 2.303 R T kcal/mol. The A factors were assigned from previous high-pressure low-temperature data of other workers assuming a four-center transition state for 1,2-HC1 elimination and a chlorine-bridged biradical transition state for vinyl chloride formation. The activation energies are in good agreement with the high-pressure results which were obtained with a conventional static system. The difference in critical energies is 4.6 kcal/mol.