Dramatic Acceleration of Olefin Epoxidation in Fluorinated Alcohols: Activation of Hydrogen Peroxide by Multiple H-Bond Networks
- 22 September 2006
- journal article
- Published by American Chemical Society (ACS) in Journal of the American Chemical Society
- Vol. 128 (41), 13412-13420
- https://doi.org/10.1021/ja0620181
Abstract
In 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) as solvent, the epoxidation of olefins by hydrogen peroxide is accelerated up to ca. 100 000-fold (relative to that in 1,4-dioxane as solvent). The mechanistic basis of this effect was investigated kinetically and theoretically. The kinetics of the epoxidation of Z-cyclooctene provided evidence that higher-order solvent aggregates (rate order in HFIP ca. 3) are responsible for the rate acceleration. Activation parameters (ΔS⧧ = −39 cal/mol·K) indicated a highly ordered transition state in the rate-determining step. In line with these findings, DFT simulations revealed a pronounced decrease of the activation barrier for oxygen transfer from H2O2 to ethene with increasing number of (specifically) coordinated HFIP molecules. The oxygen transfer was unambiguously identified as a polar concerted process. Simulations (combined DFT and MP2) of the epoxidation of Z-butene were in excellent agreement with the experimental data obtained in the epoxidation of Z-cyclooctene (activation enthalpy, entropy, and kinetic rate order in HFIP of 3), supporting the validity of our mechanistic model.Keywords
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