Reflux under an inert atmosphere

Schlenk tubes can be heated to reflux in a similar way to using round-bottomed flasks and condensers. The exact method used will vary a little depending on the exact reaction (solvent, boiling point, quantities, size of Schlenk tube etc). The instructions below assume a reflux setup where a condenser is required but this may not always be necessary (e.g. for small volumes of high boiling solvents in large Schlenk tubes the glass walls of the Schlenk tube may provide enough surface area for condensation).

1. The Schlenk tube for reflux should be placed under a nitrogen atmosphere with the stopper attached. Ideally a socket/stopper Schlenk tube should be used as a condenser is designed to be used with the cone end at the bottom.

2. Obtain a condenser with a suitable ground glass joint which will fit the Schlenk tube. Ideally adapters should be avoided where possible. If an adapter is required, then all the joint should be greased appropriately.

3. A swan-necked adapter should be connected to one of the rubber hoses of the Schlenk line. The joint should be greased and fitted to the top of the condenser.

4. There are two ways to flush a condenser with gas:

• Open the gas manifold to the swan-necked adapter and allow the condenser to be flushed with a steady flow of gas.

• Fit an empty flask (or Viking helmet) to the bottom of the condenser in order to carry out vacuum/gas purge cycles (the same way as you would purge a Schlenk tube). Leave it under an inert gas atmosphere with the double oblique tap open to the gas manifold and keep the empty flask/helmet in place until ready to connect to the Schlenk tube.

5. Remove the stopper from the Schlenk tube (double check the flask is still connected to the gas manifold) and insert the condenser into the Schlenk tube (after removing the empty flask/helmet if this was used).

6. Close the Schlenk tube tap but leave the double oblique taps (both from the Schlenk and the swan neck) open to the gas section of the manifold.

Heating Schlenk tubes is generally achieved using an oil bath on a stirrer-hotplate, and the Schlenk tube/condenser setup is used in an analogous way to conventional refluxes.

Note: Never heat a completely enclosed system. No reaction should be left as a sealed system in case there is a pressure build-up, as this can result in explosions. Connection to the gas manifold allows pressure to be released via the oil bubbler. You should have your apparatus checked by a demonstrator before heating.