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Schlenk Line - Use


Schlenk lines (also called vacuum/gas manifolds) are very common in air-free synthesis, especially when working with air/water-sensitive or pyrophoric materials. This tutorial is intended to complement training and is NOT a replacement for on-the-job training! A refresher of important safety points under "Schlenk Line - Safety Notes" and suggestions on setup under "Schlenk line - Installation" should be reviewed prior to this page.






Common Schlenk Line Configuration:

Every researcher has his/her own preferences when it comes to setting up a Schlenk line, including the type of manifold, adapters, glassware used, bubblers, configuration, etc.

This page walks through the use of a Schlenk line using the example pictured to the left, which is also the manifold described in the section titled "Schlenk Line - Setup."







  Vacuum Line:

The vacuum on the manifold depicted is operated using the top portion of the Schlenk line. Vacuum is pulled using a vacuum pump in
a vacuum cabinet under the hood (not pictured). A thermocouple on the end of the line opposite the vacuum pump connects to a vacuum gauge and allows the vacuum pressure to be monitored. A solvent trap is used in-line just before the vacuum in order to protect the pump, and when necessary is surrounded by liquid nitrogen using a special dewar to freeze solvents coming off of any reactions.






  Gas Line:

The gas on the manifold depicted is operated using the bottom portion of the Schlenk line. Gas (nitrogen or argon) is fed through the bottom of the manifold. At the output of the gas line is an oil bubbler that allows the pressure in the system to be released and confirms that gas is flowing through the system.








Valves (or Keys):

Vacuum and gas are introduced into a reaction by twisting on the manifold valves. On the more common Schlenk lines in the Foundry, these valves are Teflon. Turning the valve clockwise closes the valve (the triangular tip of the teflon makes a visible seal on the glass). Turning the valve counter-clockwise opens the valve, by pulling the triangular point of the teflon away from the hole that leads to the manifold. It is important that you do not have these two valves both open at the same time!


SET-UP:
  1. Inspect the Schlenk set-up
    • Ensure that the surrounding space in the fume hood is clear of debris and clutter.
    • Ensure there are no visible cracks in any of the glassware to be used.
    • Check that all tubing, dewars, glassware (including the solvent trap) are clean and completely dry.
  2. Close all vacuum valves
  3. Turn on the vacuum pump
    • Remember that some vacuum pumps take up to 30minutes to reach peak efficiency.
    • Monitor the vacuum gauge until the vacuum level is stable - typically a vacuum line should hold at or below ~60 microns without liquid nitrogen.
    • DO NOT PROCEED if the vacuum is not stable. Leaks in the line are a hazard and must be identified and fixed before continuing.
  4. Once the vacuum is good and stable, raise the vacuum trap and add liquid nitrogen
    • Liquid nitrogen is cold and can burn you, so use appropriate PPE.
    • Liquid nitrogen will boil off slightly and can bump up while the glassware is initially cooling - so be careful and top off your dewar.
    • You will note that your vacuum will go down once liquid nitrogen is introduced, which is expected and appreciated!
    • The lower your vacuum level the better your vacuum - really sensitive reactions should ideally have a vacuum around or below 10microns if possible.
  5. Run your reaction as intended.


TAKE-DOWN:

  1. When finished using the Schlenk line, clear the space surrounding the manifold of debris and clutter.
  2. Lower and remove the liquid nitrogen dewar from the solvent trap.
    • Remember to use proper PPE when handling liquid-nitrogen containing recepticals.
  3. Turn off the vacuum pump.
  4. Vent the vacuum line by slowly opening one of the valves on the vacuum line.
    • Leave the valve open while the frozen solvent in the trap thaws completely (or until you use the manifold again).
    • Neglecting to vent the line may result in an explosion as the melting organics increase the vapor pressure, so don't forget this step.
    • If liquid oxygen is observed (a faint blue cloud), close the fume hood sash and leave the area immediately until the oxygen dissipates. Notify those nearby of the potential danger and check back in 20-30minutes (see suggestions under "Schlenk Line - Safety Notes")
  5. Allow any frozen organics to thaw to room temperature before detaching the trap.
  6. Dispose of solvents in the appropriate waste container.
  7. Clean your work area and wipe down your bench.
  8. Wash the solvent trap and dry in a 120C oven until the next use.
  9. Smile and walk away!





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