407-59-0Relevant articles and documents
Threshold energies and unimolecular rate constants for elimination of HF from chemically activated CF3CH2CH3 and CF3CH2CF3: Effect of CH3 and CF3 substituents at the β-carbon and implications about the transition state
Ferguson, Heather A.,Ferguson, John D.,Holmes, Bert E.
, p. 5393 - 5397 (1998)
Chemically activated CF3CH2CF3 was prepared with 104 kcal/mol of internal energy by the combination of CF3CH2 and CF3 radicals, and chemically activated CF3CH2CH3 was prepared with 101 and 95 kcal/mol by combination of CF3 and CH2CH3 radicals and by combination of CF3CH2 and CH3 radicals, respectively. The experimental rate constants for unimolecular 1,2-dehydrofluorination were 1.2 × 105 s-1 for CF3CH2CF3 and 3.2 × 106 s-1 for CF3CH2CH3 with 95 kcal/mol and 2.0 × 107 s-1 with 101 kcal/mol of energy. Fitting the calculated rate constants for HF elimination from RRKM theory to the experimental values provided threshold energies, E0, of 73 kcal/mol for CF3CH2CF3 and 62 kcal/mol for CF3CH2CH3. Comparing these threshold energies to those for CF3CH3 and CF3CH2Cl illustrates that replacing the hydrogen of CF3CH3 with CH3 lowers the E0 by 6 kcal/mol and replacing with CF3 or Cl raises the E0 by 5 and 8 kcal/mol, respectively. The CF3 substituent, an electron acceptor, increases the E0 an amount similar to Cl, suggesting that chlorine substituents also prefer to withdraw electron density from the β-carbon. As the HF transition state forms, it appears that electron density flows from the departing hydrogen to the β-carbon and from the β to the α-carbon, to the α-carbon from its substituents, but the α-carbon releases most of the incoming electron density to the departing fluorine. The present work supports this scenario because electron-donating substituents, such as CH3, on either carbon would reduce the E0 as they aid the flow of negative charge, while electron-withdrawing substituents such as Cl, F, and CF3 would raise the E0 for HF elimination because they hinder the flow of electron density.
Method of Hydrodechlorination to Produce Dihydrofluorinated Olefins
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Page/Page column 5, (2009/01/24)
Disclosed herein is a process for the preparation of fluorine-containing olefins comprising contacting a chlorofluoroalkene with hydrogen in the presence of a catalyst at a temperature sufficient to cause replacement of the chlorine substituents with hydrogen. Also disclosed is a catalyst composition for the hydrodechlorination of chlorofluoroalkenes comprising copper metal deposited on a support.
