Residual solvent removal

When filtering solids (e.g. using a Buchner or sinter funnel), it is normal to let them air dry over vacuum before collecting the product. This air-drying is carried out in order to minimise the presence of residual solvents in the material. The removal of residual solvent from compounds can also aid their air-stability. Many compounds have reasonable air-stability, but very poor stability in solution, so the removal of solvent can allow the compounds to be isolated and handled outside of the inert conditions of a Schlenk tube.

The removal of residual solvent can be achieved by exposing the desired solid (or liquid) of interest to vacuum. Consideration needs to be given to the volatility (for both solids and liquids), as it is clearly undesirable to lose product by evaporation or sublimation.

1. These steps assume the compound is in a sealed Schlenk tube which is connected to the gas manifold.

2. Close the side arm tap to the flask and switch the double-oblique tube to the vacuum manifold.

3. Slowly open the side arm tap, and carefully control the vacuum to the solid. Any solvent will begin to evaporate and may cause the solid to bump in the flask. It may be necessary to reclose the side arm tap to avoid losing any material. The pressure reading may increase significantly as solvent vapours reduce the effective vacuum.

4. As the solvent evaporates, continue opening the tap until the flask is fully open to vacuum and allow the compound to dry.

5. When all the solvent has been removed, the pressure reading on the vacuum should return to previous levels.