- Isergonic relationship in the acid-catalyzed hydrolysis of carboxylic esters with hydrogen-bonding capability
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The average value of the enthalpies of activation for the acid-catalyzed hydrolyses of ethyl 2-hydroxypropanoate and five acetate esters with hydrogen bonding capability is 57 ± 7 kJ mol-1 (p = 0.05). This value is 11 kJ mol-1 lower than the mean observed for primary and secondary alkyl acetates and ethyl alkanoates, measured in water and in mixtures of water with organic solvent with high water content. The difference is attributed to tighter transition-state complex hydration via hydrogen bonding, relative to reactant ester species. Enthalpy-entropy compensation with an isokinetic temperature of 346 K was found to be valid at p 0.05, a value typical for solvent-mediated kinetic effects. Copyright
- Mata-Segreda, Julio F.
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p. 567 - 571
(2007/10/03)
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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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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 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 deg C gave the corresponding TFVEs in 55-63percent yields.Thus, 1--1,2,2-trifluoroethene and 1--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.1 For example, thermolysis of sodium 2--2,3,3,3-tetrafluoropropionate gave a trifluoroacetate ester, 2-(2-ethoxyethoxy)ethyl trifluoroacetate.Variable temperature 19F NMR spectroscopy of trimethylsilyl 2--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.
- Lousenberg, Robert D.,Shoichet, Molly S.
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p. 7844 - 7849
(2007/10/03)
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