Schlenk Lines Transfer of Solvents

Source: Hsin-Chun Chiu and Tyler J. Morin, laboratory of Dr. Ian Tonks—University of Minnesota Twin Cities

Schlenk lines and high vacuum lines are both used to exclude moisture and oxygen from reactions by running reactions under a slight overpressure of inert gas (usually N₂ or Ar) or under vacuum. Vacuum transfer has been developed as a method separate solvents (other volatile reagents) from drying agents (or other nonvolatile agents) and dispense them to reaction or storage vessels while maintaining an air-free environment. Similar to thermal distillations, vacuum transfer separates solvents by vaporizing and condensing them in another receiving vessel; however, vacuum transfers utilize the low pressure in the manifolds of Schlenk and high vacuum lines to lower boiling points to room temperature or below, allowing for cryogenic distillations. This technique can provide a safer alternative to thermal distillation for the collection of air- and moisture-free solvents. After the vacuum transfer, the water content of the collected solvent can be tested quantitatively by Karl Fischer titration, qualitatively by titration with a Na/Ph₂CO solution, or by ¹H NMR spectroscopy.

1. Using Schlenk Lines

1 Start Up

Make sure that all working ports on the manifold are closed, and that all joints are properly greased with high vacuum grease.
Attach the solvent trap(s) to the vacuum line, and seal by turning on the vacuum pump. NOTE: Each vacuum pump has its own “unique” sound when air is actively being pumped out of the system. It is important to “get to know” the regular sounds that your vacuum makes while p

The picture was taken of the vacuum transfer in progress (Figure 2) and after the Na/Ph₂CO titration titration was performed (Figure 3).

Solvents collected via this method have been tested by ketyl titration. Figure 3 shows the common possible outcomes of the ketyl test. The purple color in (a) indicates < 10 ppm H₂O in the solvent; while the blue and colorless solutions indicate a wetter solvent that needs further pu

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