Solvophobic Acceleration of Diels-Alder Reactions in Supercritical Carbon Dioxide
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- 作者：Jin Qian ; Michael T. Timko ; Andrew J. Allen ; Christopher J. Russell ; Bozena Winnik ; Brian Buckley ; Jeffrey I. Steinfeld ; and Jefferson W. Tester
- 刊名：Journal of the American Chemical Society
- 出版年：2004
- 出版时间：May 5, 2004
- 年：2004
- 卷：126
- 期：17
- 页码：5465 - 5474
- 全文大小：199K
- 年卷期：v.126,no.17(May 5, 2004)
- ISSN：1520-5126
文摘
The rate of the Diels-Alder reaction between N-ethylmaleimide and 9-hydroxymethylanthracenein supercritical carbon dioxide (scCO2) was determined by following the disappearance of 9-hydroxymethylanthracene with in situ UV/vis absorption spectroscopy. The reaction conditions were 45-75 
Cand 90-190 bar, which correspond to fluid densities (based on pure carbon dioxide) ranging betweenapproximately 340 and 730 kg m-3. The measured reaction rate at low scCO2 fluid densities was nearly25× faster than that reported in acetonitrile at the same temperature (45 C). An inverse relationship betweenreaction rate and fluid density/pressure was observed at all temperatures in scCO2. The apparent activationvolumes were large and positive (350 cm3 mol-1) and only a weak function of reduced temperature. Asolvophobic mechanism analogous to those observed in conventional solvents is postulated to describe(a) the rate acceleration observed for this reaction in scCO2 relative to that in acetonitrile, (b) the observedrelationship between reaction rate and pressure/temperature/density, and (c) the large, positive activationvolumes. Solubility measurements in scCO2, rate measurements in conventional solvents, and an empiricalcorrelation are used to support this theory. Our results advance the general understanding of reactivity insupercritical fluids and provide a rationale for selecting reactions which can be accelerated when conductedin scCO2.
Cand 90-190 bar, which correspond to fluid densities (based on pure carbon dioxide) ranging betweenapproximately 340 and 730 kg m-3. The measured reaction rate at low scCO2 fluid densities was nearly25× faster than that reported in acetonitrile at the same temperature (45 C). An inverse relationship betweenreaction rate and fluid density/pressure was observed at all temperatures in scCO2. The apparent activationvolumes were large and positive (350 cm3 mol-1) and only a weak function of reduced temperature. Asolvophobic mechanism analogous to those observed in conventional solvents is postulated to describe(a) the rate acceleration observed for this reaction in scCO2 relative to that in acetonitrile, (b) the observedrelationship between reaction rate and pressure/temperature/density, and (c) the large, positive activationvolumes. Solubility measurements in scCO2, rate measurements in conventional solvents, and an empiricalcorrelation are used to support this theory. Our results advance the general understanding of reactivity insupercritical fluids and provide a rationale for selecting reactions which can be accelerated when conductedin scCO2.