Refluxing Under an Inert Atmosphere

Method A

Step 1: Cycle a reflux condenser onto the Schlenk line. Attach a gas inlet adapter to the top of the condenser, and a Schlenk cap or small round bottom flask to the bottom of the condenser, greasing the male joints and ensuring a uniform seal. Place under vacuum.

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Cycling a reflux condenser onto the Schlenk line.

Step 2: Once the reflux condenser has been cycled onto the Schlenk line, backfill with inert gas and attach to the Schlenk flask under a flow of inert gas.

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Attaching the reflux condenser to the Schlenk flask under a flow of inert gas.

Step 3: Close the stopcock on the Schlenk flask and lower the flask into a heating mantle or oil bath. Connect the water tubing to the reflux condenser and begin heating.

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Compete reflux set-up.

It is recommended to set up a reflux towards the end of the day to run overnight or over the weekend since it is advised not to perform other reactions on the Schlenk line.

Method B

If the reflux is expected to liberate nasty by-products that may contaminate the Schlenk line, then it advised to use an external bubbler.

Step 1: Assemble a reflux condenser and Dreschel head (gas inlet/outlet adapter), greasing the male joints and ensuring a uniform seal. Connect an external oil bubbler to the gas outlet and then attach the gas inlet to the Schlenk line tubing. Open to the inert gas and purge the glassware for 30-60 seconds.

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Purging a reflux condenser equipped with an external bubbler.

Step 2: Attach the reflux condenser to the Schlenk flask under a flow of inert gas. The bubbler will begin bubbling at this point – adjust the gas flow so that it bubbles once every few seconds.

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Attaching the reflux condenser under a flow of inert gas.

Step 3: Close the stopcock on the Schlenk flask and lower the flask into a heating mantle or oil bath. Connect the water tubing to the reflux condenser and begin heating. It may be necessary to adjust the inert gas flow rate as the system approaches to the desired temperature.

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Complete reflux set-up with external bubbler.

Step 4: After the desired duration of heating, cool the reaction mixture to room temperature. Increase the inert gas flow rate whilst cooling to prevent oil suck-back. Once cooled to room temperature, open the stopcock on the Schlenk flask and replace the reflux condenser with a greased stopper under a flow of inert gas.

Method C

Reactions that require prolonged heating, and do not liberate gaseous by-products, can be heated directly in J. Young’s ampoules without the need for a reflux condenser. Since this method does build up pressure within a sealed vessel, it is essential that the reaction vessel is suitable for such use. It is advised not to heat beyond the boiling point of the solvent unless specialist heavy-walled pressure vessels are used in tandem with a blast shield.

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Heating in sealed ampoule.