"Simple and Efficient Microwave-Assisted Hydrogenation Reactions at Moderate Temperature and Pressure" (pdf), G. S. Vanier, SYNLETT 1, 131 - 135, 2007
Flyer "Reaktionen mit Gaszugabe - Gas Addition Accessory" (pdf)
Simple and Efficient Microwave-Assisted Hydrogenation Reactions at Moderate Temperatures and Pressures (pdf)
Preparation of Ruthenium and Osmium Carbonyl Complexes Using Microwave Heating: Demonstrating the Use of a Gas-Loading Acessorx and Real-Time Reaction Monitoring by Means of a Digital Camera (pdf)
Hydrierungen in der Mikrowelle
Kit für Reaktionen unter Gaszugabe (Hydrierungen, Carbonylierungen, Hydroformylierungen, etc.)
Dieses Kit ermöglicht die Durchführung von mikrowellenaktivierten Reaktionen unter Gaszugabe im Discover wie z. B. Hydrierungen, Carbonylierungen, Hydroformylierungen, etc. Die Temperatur wird In-Situ mittels einer mikrowellentransparenten Faseroptischen Temperatursonde erfasst und der Reaktionsverlauf dadurch gesteuert.
Go Ahead! Give it some Gas!
The most common use of microwave technology for organic synthesis is to run reactions in sealed vials at elevated temperatures and pressures. The microwave reaction vials can be considered "mini-pressure cookers" and, though they work well for performing many types of chemistries, they are completely sealed and work with non-invasive pressure and temperature measurement devices. This has been a limiting factor for the sealed vessel technology, as chemists cannot add gaseous reagents, such as carbon monoxide or hydrogen. A alternative is the use of solid sources to generate in-situ gases, but this has the potential problem of generating excessive pressure, as well as additional purification.
What’s a chemist to do? That’s precisely what we asked ourselves. The answer came in the form of a simple accessory for the introduction of gas reagents into a sealed vial, which safely extended the benefits of microwave energy to gas addition reactions.
The Gas Addition Accessory is designed to be used with the Discover® S-Class Microwave Synthesizer, but can also be used with earlier Discover Systems.
The Gas Addition Accessory extends the range of chemistries that can benefit from microwave enhancement. It consists of a modified vial closure design with two ports and an external valve panel assembly for gas purging and evacuation of the reaction vial. The two ports allow for the insertion of a temperature probe and a gas line while still maintaining a completely sealed vessel. The gas line is connected to the external valve panel, which has a four-way valve connected to the vacuum source, gas supply, an integral pressure sensor, and the atmosphere. The chemist manipulates the valve position to evacuate/purge the reaction mixture prior to the microwave irradiation step, to put the pressure sensor inline while applying microwave energy, and to vent the reaction mixture after the cooling step.
This accessory allows you to safely prepressurize your reaction mixture with hydrogen, carbon monoxide, or other gases/gas mixtures for your microwave-driven chemistry. Because microwave energy is transferred kinetically, not thermally, hydrogenations, carbonylations, hydroformylations and other reactions using gaseous reagents can be run at conventional temperatures and pressures, as well as at elevated reaction conditions.
The Discover Gas Addition Accessory offers chemists a safe, effective way to incorporate gaseous reagents into their reactions, while still reaping the benefits of using microwave energy to drive their chemistries. So, go ahead! Give your reactions some gas and don’t just imagine the possibilities, discover them!
Simple and Efficient Microwave-Assisted Hydrogenation Reactions:
Hydrogenation is one of the most powerful transformations in synthetic chemistry and one that often requires long reaction times to affect complete conversion to product. In addition, hydrogenations can also require harsh reaction conditions, such as high pressures and/or temperatures.
As with several other types of metal-catalyzed reactions, hydrogenation reactions can benefit from the use of microwave irradiation to accelerate the reaction and improve yields. The recent development of the Gas Addition Accessory to allow the introduction of gas reagents into a sealed reaction vial provides chemists with an additional tool to further capitalize on the benefits of microwave technology. Vanier discussed the development of a generally applicable hydrogenation method under microwave irradiation (SYNLETT 2007, No. 1, pp 0131 - 0135).
The optimized conditions of temperatures of 80 oC and pressures of 50 psi (3.3 bar) provided yields in a range of 85 - 100% for a variety of alkenes, alkynes, and nitrobenzenes Reaction times ranged from 3-20 minutes with a Pd/C catalyst loading of 1 mole %.
Of particular note is the direct comparison of the microwave to conventional heating for an example hydrogenation reaction. The comparison was achieved by performing the hydrogenation of a diene under identical reaction conditions in a preheated oil bath and the microwave system. The exact same temperature, pressure, and time were used in the oil bath experiment with careful control over the temperature rise rate to ensure accurate reproduction of the microwave reaction conditions. The hydrogenation performed in the microwave resulted in complete conversion to product, while the reaction performed in the oil bath resulted in only 55% conversion. These results indicate that the microwave does indeed both accelerate the chemistry and influence the outcome of the hydrogenation reaction.
"Reaktionen mit Gaszugabe - Gas Addition Accessory" (PDF)