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Synthesis of Trifluorovinyl Ethers Incorporating Functionalized Hydrocarbon Ether Groups:  Insight into the Mechanism of Trifluorovinyl Ether Formation from Trimethylsilyl 2-Alkoxy-2,3,3,3-tetrafluoropropionates

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journal contribution
posted on 31.10.1997, 00:00 by Robert D. Lousenberg, Molly S. Shoichet
Novel trifluorovinyl ethers (TFVEs, ROCFCF2), where R is an oligoether, were synthesized from the corresponding sodium alkoxide and hexafluoropropene oxide. The sodium alkoxide ring opened hexafluoropropene oxide at the more highly substituted carbon (C2) to give the 2-alkoxy-2,3,3,3-tetrafluoropropionic acid ester incorporating 2 equiv of the alcohol, ROCF(CF3)CO2R. Hydrolysis of the ester and reaction of the resulting sodium 2-alkoxy-2,3,3,3-tetrafluoropropionate with chlorotrimethylsilane gave the trimethylsilyl 2-alkoxy-2,3,3,3-tetrafluoropropionate, ROCF(CF3)CO2Si(CH3)3. Gas phase vacuum thermolysis of the trimethylsilyl ester at 140−150 °C gave the corresponding TFVEs in 55−63% yields. Thus, 1-[2-(ethoxyethoxy)ethoxy]-1,2,2-trifluoroethene and 1-[2-(2-tert-butoxyethoxy)ethoxy]-1,2,2-trifluoroethene were synthesized from 2-(2-ethoxyethoxy)ethanol and 2-(2-tert-butoxyethoxy)ethanol, respectively. Interestingly, thermolysis of sodium or potassium 2-alkoxy-2,3,3,3-tetrafluoropropionates resulted in negligible to low yields of TFVEs. For example, thermolysis of sodium 2-[2-(ethoxyethoxy)ethoxy]-2,3,3,3-tetrafluoropropionate gave a trifluoroacetate ester, 2-(2-ethoxyethoxy)ethyl trifluoroacetate. Variable temperature 19F NMR spectroscopy of trimethylsilyl 2-[2-(ethoxyethoxy)ethoxy]-2,3,3,3-tetrafluoropropionate suggests that an equilibrium exists between two structural conformations of these trimethylsilyl esters:  one in which there is an intramolecular “interaction” of silicon with fluorine and one in which there is no silicon−fluorine interaction. This interaction may affect the outcome of the trimethylsilyl ester thermolysis.