Flame drying of glassware

For reactions which are particularly sensitive towards the presence of water, it may be necessary to flame dry glassware prior to use. This technique follows the principles of evacuating and refilling glassware using vacuum and nitrogen cycles, but with the addition of the glassware being heated during the vacuum cycles.

Historically, the heating of glassware was carried out using a Bunsen burner on a blue flame, although nowadays it is more common to use an electric heat gun. By heating the glassware under vacuum, any residual traces of water on the glassware will be evaporated and evacuated from the flask.

Flame drying of Schlenk tubes is fairly common for very sensitive reactions. Particularly where tubes are flame dried, back-filled with nitrogen, then taken into a glove box to be charged with a compound.

Method

The method follows the general approach for evacuating and back filling a Schlenk tube. When the tube is being evacuated, the glassware is heated using either a Bunsen burner or electric heat gun. Care should be taken to ensure the glassware is evenly heated, particularly avoiding any 'hotspots' being formed on the glass through overheating a section. Overheating of a section of glass can result in the glass becoming malleable to be 'sucked' in by the vacuum, which can be hazardous.

The use of flame drying will result in glassware becoming very hot, and care needs to be taken to avoid burns or other injuries. Glassware should be allowed to slowly cool down. Sudden temperature changes can result in the glass fracturing. Glassware should be allowed to fully cool before introducing any chemicals into the glassware.