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Microwave-Assisted Organic Synthesis in Near-Critical Water at 300 <sup>o</sup>C. A Proof-of-Concept Study
EP20437
Poster Title: Microwave-Assisted Organic Synthesis in Near-Critical Water at 300 oC. A Proof-of-Concept Study
Submitted on 19 Dec 2013
Author(s): Jennifer M. Kremsner and C. Oliver Kappe
Affiliations: Karl-Franzens-University Graz
Poster Views: 977
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Poster Information
Abstract: Chemical processes often employ large amounts of hazardous and toxic solvents. Therefore, organic chemists are requested to investigate clean, economical an environmentally safer methodologies.

One of the most promising approaches uses water as an alternative reaction medium. Besides reactions in water under ambient or slightly elevated temperature (<100 oC) the so-called near-critical (also termed subcritical) region of water at temperatures between 200–300 oC is of great importance to organic synthesis.

At 250 oC, water exhibits a density and polarity similar to those of acetonitrile at room temperature. The dielectric constant of water drops rapidly with temperature, and at 250 oC has fallen from 78.5 (at 25 oC) to 27.5.

Most importantly, the ionic product of water is increased by three orders of magnitude on going from room temperature to 250 oC. Near critical water (NCW) can therefore act as an acid, base, or acid-base bicatalyst without the need for costly and cumbersome neutralization and catalyst regeneration.

Herein we demonstrate the feasibility of performing microwave-assisted organic transformations like the hydrolysis of esters or amides, the hydration of alkynes, Diels Alder cycloadditions, pinacol rearrangements and the Fischer indole synthesis without the addition of an acid or basic catalyst in the 270–300 oC temperature range.[1]

For this purpose, a dedicated multimode microwave reactor (2.45 GHz, 1400 W) was utilized allowing to perform reactions in water as solvent in heavy-walled quartz reaction vessels on a 15–400 mL scale with operation limits of 80 bars of pressure and close to 300 oC temperature.[2]

[1]  Kremsner, J. M.; Kappe, C. O. Eur. J. Org. Chem. 2005, in press.
[2] Stadler, A.;  Yousefi, B. H.; Dallinger, D.; Walla, P.; Van der Eycken, E.; Kaval, N.; Kappe, C. O. Org. Process Res. Dev., 2003, 7, 707.
Summary: Demonstrated here is the feasibility of performing microwave-assisted organic transformations like the hydrolysis of esters or amides, the hydration of alkynes, Diels Alder cycloadditions, pinacol rearrangements and the Fischer indole synthesis without the addition of an acid or basic catalyst in the 270–300 oC temperature range.Report abuse »
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