Schlenk flask

A Schlenk flask, or Schlenk tube is a reaction vessel typically used in air sensitive chemistry, invented by Wilhelm Schlenk. They have a side arm fitted with a teflon or ground glass stopcock which allows the vessel to be evacuated or filled with gases (usually inert gases like nitrogen or argon). These flasks are often connected to Schlenk lines which allow both operations to be done easily.

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Schlenk flasks and Schlenk tubes are made of borosilicate glass such as Pyrex, usually used in the construction of laboratory glassware.

Schlenk flasks are round bottomed, while Schlenk tubes are elongated. They may be purchased off-the-shelf from laboratory suppliers, or made from round bottom flasks or glass tubing by a skilled glassblower.

Evacuating a Schlenk flask

Before solvent or reagents are introduced into a Schlenk flask, its atmosphere must be exchanged with inert gas. One common method for exchanging the atmosphere involves flushing the flask with through the side arm and out the ground glass joint. This approach is impractical for large flasks and complex apparatus. Alternatively, the atmosphere can be exchanged by "vac-refill" cycles. Evacuation of the flask to 1 mm and then replenishing the atmosphere with 760 mm inert gas leaves 0.13 % of the original atmosphere ((1/760)x 100%). Two such vac-refill cycles leaves 0.000173% (i.e (1/760)² x 100%). This vac-refill cycle is convenient with a Schlenk line. Most Schlenk lines easily and quickly achieve a vacuum of 1 mm Hg.^[1]

References

1. ^ The Manipulation of Air-Sensitive Compounds, by Duward F. Shriver and M. A. Drezdzon 1986, J. Wiley and Sons: New York. ISBN 0-471-86773-X.