Introduction to Schlenk Lines

A Schlenk line consists of two separate glass manifolds one under vacuum and one containing an inert gas, such as N₂. These manifolds can be connected to a reaction flask using a double-oblique tap and rubber tubing.

A Schlenk line allows the manipulation of compounds in an inert atmosphere by using a gas that is both oxygen and water-free. The double oblique tap allows reaction flasks to be evacuated of air, then refilled to atmospheric pressure with an inert gas. This process of evacuation and refilling is usually repeated several times in order to ensure that all traces of air have been removed from the flask. Typically three cycles are carried out.

The vacuum for a Schlenk line is typically provided by a rotary pump, and the pressure is usually measured using a Pirani gauge which can typically display pressures between 1 and 10⁻² mbar. The gauge should indicate a pressure less than 10⁻¹ mbar when under active vacuum. If your gauge is reading a higher pressure then you may have a leak in your system and should consult a demonstrator.

To prevent solvent vapours from entering the pump, a liquid-N₂ filled Dewar is placed between the pump and the vacuum manifold. This will condense solvent vapours in the trap and therefore minimise any solvent vapours entering the pump. However, as the boiling point of liquid nitrogen (–196 °C) is below that for liquid oxygen (–183 °C), it is possible to condense liquid oxygen in the cold trap if the manifold is left open to the air. It is therefore crucial that you do not place a liquid-N₂ filled Dewar around a cold trap that is not under vacuum.