Kinetics of the I2-catalyzed isomerization of allyl chloride to cis- and trans-1-chloro-1-propene. The stabilization energy of the chloroallyl radical

✍ Scribed by Ze'ev B. Alfassi; David M. Golden; Sidney W. Benson

• Publisher: John Wiley and Sons
• Year: 1973
• Tongue: English
• Weight: 664 KB
• Volume: 5
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.550050114

✦ Synopsis

Abstract

The I~2~‐catalyzed isomerization of allyl chloride to cis‐ and trans‐ l‐chloro‐l‐propene was measured in a static system in the temperature range 225–329°C. Propylene was found as a side product, mainly at the lower temperatures. The rate constant for an abstraction of a hydrogen atom from allyl chloride by an iodine atom was found to obey the equation log [k,/M^−1^ sec^−1^] = (10.5 ± 0.2) −; (18.3 ± 10.4)/θ, where θ is 2.303__RT__ in kcal/mole. Using this activation energy together with 1 ± 1 kcal/mole for the activation energy for the reaction of HI with alkyl radicals gives DH^0^ (CH~2~CHCHClH) = 88.6 ± 1.1 kcal/mole, and 7.4 ± 1.5 kcal/mole as the stabilization energy (SE) of the chloroallyl radical. Using the results of Abell and Adolf on allyl fluoride and allyl bromide, we conclude DH^0^ (CH~2~CHCHFH) = 88.6 ± 1.1 and DH^0^ (CH~2~CHCHBrH) = 89.4 ± 1.1 kcal/ mole; the SE of the corresponding radicals are 7.4 ± 2.2 and 7.8 ± 1.5 kcal/mole. The bond dissociation energies of the CH bonds in the allyl halides are similar to that of propene, while the SE values are about 2 kcal/mole less than in the allyl radical, resulting perhaps more from the stabilization of alkyl radicals by α‐halogen atoms than from differences in the unsaturated systems.