Glassware used for the manipulation and preparation of air- and moisture-sensitive compounds must be rigorously dried and free of air prior to use. Schlenk flasks and items are typically stored in ovens above 100 ºC to remove any residual or adsorbed water.
Attaching a new Schlenk flask or reaction vessel to the Schlenk line
Step 1: Remove a Schlenk flask, magnetic stir bar, ground glass stopper and stopcock from the oven using heat resistant gloves.
Step 2: Grease the stopper and stopcock by applying two strips of grease along opposite sides and insert them into their respective female joints with twisting to evenly spread the grease and form a seal. If the grease looks streaky or if the stopper and stopcock don’t twist smoothly then more grease should be applied. Ensure that the grease does not block the gas inlet/outlet hole on the stopcock. Secure the stopper with a clip, and the stopcock with a PTFE washer, nut and O-ring.
Step 3: Attach the Schlenk flask to the rubber tubing of the Schlenk line and open the stopcock to the vacuum. For moisture sensitive reactions, it is advised to heat the Schlenk flask whilst under vacuum with a heat gun or bunsen burner.
Step 4: After 15 minutes, close the vacuum inlet stopcock and slowly backfill the flask with inert gas. Repeat the vacuum (5-10 minutes) and inert gas cycles two more times.
Cycling sealed vessels already under an inert atmosphere:
For ampoules and flasks that are already under an atmosphere of inert gas, three vacuum/inert gas cycles are required to evacuate the air within the Schlenk line tubing and flask side arm. The duration of time left under vacuum will vary depending on the volume of ‘air’ to remove, but 30-60 seconds per cycle should generally suffice. This is more commonly referred to as ‘cycling’ onto the Schlenk line.