Schlenk line

A Schlenk line with four ports. The cold trap is on the right
Close-up view, showing the double-oblique stopcock, which allows vacuum (rear line) or inert gas (front line) to be selected

The Schlenk line (also vacuum gas manifold) is a commonly used chemistry apparatus developed by Wilhelm Schlenk. It consists of a dual manifold with several ports.[1] One manifold is connected to a source of purified inert gas, while the other is connected to a vacuum pump. The inert-gas line is vented through an oil bubbler, while solvent vapors and gaseous reaction products are prevented from contaminating the vacuum pump by a liquid-nitrogen or dry-ice/acetone cold trap. Special stopcocks or Teflon taps allow vacuum or inert gas to be selected without the need for placing the sample on a separate line.

Schlenk lines are useful for safely and successfully manipulating air-sensitive compounds. The vacuum is also often used to remove the last traces of solvent from a sample. Vacuum and gas manifolds often have many ports and lines, and with care, it is possible for several reactions or operations to be run simultaneously.

When the reagents are highly susceptible to oxidation, traces of oxygen may pose a problem. Then, for the removal of oxygen below the ppm level, the inert gas needs to be purified by passing it through a deoxygenation catalyst.[2] This is usually a column of copper(I) or manganese(II) oxide, which reacts with oxygen traces present in the inert gas.

Techniques

The main techniques associated with the use of a Schlenk line include:

Glassware are usually connected by tightly fitting and greased ground glass joints. Round bends of glass tubing with ground glass joints may be used to adjust the orientation of various vessels.

Filtration under inert conditions poses a special challenge that is usually tackled with specialized glassware. A Schlenk filter consists of sintered glass funnel fitted with joints and stopcocks. By fitting the pre-dried funnel and receiving flask to the reaction flask against a flow of nitrogen, carefully inverting the set-up, and turning on the vacuum appropriately, the filtration may be accomplished with minimal exposure to air.

Dangers

The main dangers associated with the use of a Schlenk line are the risks of an implosion or explosion. An implosion can occur due to the use of vacuum and flaws in the glass apparatus.

An explosion can occur due to the common use of liquid nitrogen in the cold trap, used to protect the vacuum pump from solvents. If a reasonable amount of air is allowed to enter the Schlenk line, liquid oxygen can condense into the cold trap as a pale blue liquid. An explosion may occur due to reaction of the liquid oxygen with any organic compounds also in the trap.

Gallery

See also

References

  1. Craig M. Davis and Kelly A. Curran (November 2007). "Manipulation of a Schlenk Line: Preparation of Tetrahydrofuran Complexes of Transition-Metal Chlorides" (abstract page). Journal of Chemical Education 84 (11): 1822–3. Bibcode:2007JChEd..84.1822D. doi:10.1021/ed084p1822.
  2. C. R. McIlwrick and C. S. Phillips The removal of oxygen from gas streams: applications in catalysis and gas chromatography, Journal of Physics E: Scientific Instruments, 1973, 6:12, 1208–10.
  3. Brown, H. C. "Organic Syntheses via Boranes" John Wiley & Sons, Inc., New York: 1975. ISBN 0-471-11280-1.

Further reading

External links

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