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Our Equipment We have one of the widest selections of state-of-the-art scientific microwave apparatus in the world. To learn more about the individual microwave systems and how we incorporate them into our research efforts, try the “Pick a Microwave!” option or click on the links below. We have: CEM Discover systems Milestone MultiSynth Biotage Initiator This array of apparatus allows us to perform chemistry from the mg to the kg scale. We can monitor and perform reactions at temperatures from -50°C to above 300°C and can pre-load reaction vessels with a reactive gas such as carbon monoxide or hydrogen. Using our Raman module, we can monitor the progress of reactions using real-time analysis. Reaction temperatures can be measured using either infrared sensors or in-situ fiber optic probes. We are therefore able to investigate the existence of non-thermal microwave effects using very controlled conditions.
The three CEM Discover microwave units we have act as the workhorses for the group. The flexibility of the system and its modular design opens avenues for a wide range of conditions and variables to be investigated, giving it great versatility in the laboratory. The Discover allows us to run reactions at up to 300°C and 300 psi in 10-mL or 80-mL sealed vessels. Additionally, open-vessel reactions can be run using conventional round-bottom flasks (up to 125 mL) equipped with a reflux condenser.
The S-Class is the newest in the CEM Discover series and their premier microwave synthesis system. By using fuzzy logic, the S-Class offers improved reaction parameter monitoring and control; a benefit to us in some of our more complex experiments. The new Synergy™ software gives us greater capability to follow reactions in real-time as well improved flexibility in data storage and output.
An interesting accessory to the Discover line is the CoolMate external cooling device. This device essentially allows us to run reactions at sub-ambient temperatures but with the introduction of significant microwave power. In principle, this could open up avenues for running reactions at room temperature or below in minutes that conventionally take many hours. Reactions involving thermally unstable substrates such as carbohydrates or main-group organometallics may benefit from this technique. In essence, this apparatus takes the concept of simultaneous cooling to an extreme. The apparatus allows us to work in temperature ranges from -50°C to 50°C, the temperature being controlled by the rate of flow of the cryogenic fluid as well as the microwave power used.
We have had experience working with the CEM Voyager unit. This allowed us to scale-up Suzuki and Heck coupling chemistry from the mg to the multigram level by interfacing with the Discover unit. It works with one 80-mL vessel in the microwave cavity. The reaction mixture is pumped into and out of the vessel by a peristaltic pump; these functions, as well as running the reaction, being computer controlled. This gives a high degree of automation to the process. The reaction mixture can be introduced into the microwave vessel from two separate feed lines. After the reaction is complete, the reaction vessel can be vented and the contents of the reactor pumped into a collection vessel. If necessary, the reactor can then be cleaned with solvent before subsequent runs.
One of the newest tools in the Leadbeater labs comes in the form of an in-situ Raman monitoring accessory for the Discover microwave unit. A Raman module (excitation source 785 nm; spectral coverage 2400 cm-1 - 200 cm-1) commercially available from EnWave Optronics has been interfaced with a Discover. A fiber-optic probe attached to the Raman module can be introduced into the microwave cavity, the laser being focused via a quartz light tube positioned close to the reaction vessel. This accessory allows for real-time monitoring of a reaction’s progress. This is important because a major problem with performing a reaction using microwave apparatus is that monitoring the reaction progress generally requires stopping it, allowing the reaction mixture to cool and then using standard analysis techniques such as IR and NMR spectroscopy. Therefore, optimization of reaction conditions such as time and temperature is often a matter of trial and error. The Raman accessory allows us to follow the course of reactions as they run.
The CEM MARS Microwave Synthesis System allows us to take reactions from the Discover to the next scale. With this instrument we can run reactions in round-bottom flasks from a capacity of 500-mL to 5 L. This allows for reactions to be scaled from a millimole scale to a multimole scale. There is an access port on the top of the microwave unit, through which a reflux condenser or distillation apparatus to be connected. The ability to perform reactions on a large scale allows us to research practical and safe methodologies for process chemistry. The Suzuki and Heck couplings, and the Knoevenagel condensation have been scaled-up to large as a 5 moles using this apparatus. We have also used the MARS for the preparation of biodiesel, a fuel derived from vegetable oil. It is also possible to perform several reactions in sealed vessels at the same time in the MARS using a rotor system. It is this configuration that has been used for adapting reactions for the undergraduate organic laboratory.
The Anton Paar Synthos 3000 is a multimode variable power scientific microwave unit. In the configuration used by us, eight quartz vessels fit in PEET jackets and load onto a rotor which allows individual pressure and external IR temperature measurement for each of the up to eight vessels and internal temperature monitoring of a single reference vessel via a wireless probe. Operating pressures of up to 80 bar are possible, this allowing us to heat reaction mixtures in water to close to 300°C (near-critical). A gas loading accessory allows us to perform reactions under up to 10 bar initial pressure of a reactive gas such as carbon monoxide or hydrogen opening new avenues for microwave-promoted carbonylation, hydroformylation and hydrogenation.
The Milestone MultiSynth is new in 2006. It can operate as either a monomode or multimode apparatus allowing for single reactions to be performed on small (0.2 – 6 mL) and larger scales (up to 1 L). Multiple reactions can also be performed; the apparatus accommodating up to 12 smaller scale vessels and up to six 40-mL capacity vessels. It also has unique "vortex agitation" feature. The vessels can be mechanically shaken during the course of the reaction to ensure homogeneity of reaction temperature. We have used the MultiSynth for rapid optimization of reaction conditions in a monomode function and then substrate screening in a multimode function.
The Milestone RotorPrep is used by us for larger scale reactions involving solid components (either as supports, catalysts or reagents). It agitates the reaction mixture by rotation like a rotary evaporator. Indeed it can even be used as a microwave heated rotary evaporator or distillation apparatus. Our recent work has focused on using the RotorPrep for the large-scale synthesis of esters.
We have access to the Milestone FlowSynth. This is a continuous flow microwave reactor that allowing chemists to take laboratory-scale reactions to an industrial-scale. With its pumping, stirring and pressure regulation technology, it is possible to perform reactions at temperatures up to 200°C, and pressures up to 280 psi. We are using this apparatus to scale-up a number of the chemistries developed on a small scale in our lab.
The Initiator is a single-mode microwave unit made by Biotage. The system allows us to run reactions from the very small (0.2 mL) to the medium (15 mL) scale using one unit. Using the Initiator, we are experimenting with reactions that require elevated temperatures and pressures, and performing some microwave power studies with its 400 W magnetron.
Like the Saab, the Biotage Advancer is a wonder of Swedish engineering. It is designed to perform reactions in a sealed vessel with a maximum working volume of 300 mL. It has the capability to process both homogeneous and heterogeneous mixtures. At the end of a reaction, the product mixture is rapidly transferred into a receiving vessel, adiabatically cooling it in the process. Extra vessel entry ports allow some flexibility, including the option of working under an inert atmosphere. |
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