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Schlenk: Distillation

In this video the procedure for a distillation under inert gas is explained.

If a solvent shall be evaporated under inert gas conditions, the Schlenk-Line can be used to achieve this. The valve of the flask is closed and the one of the line is opened to vacuum. Now the valve of the flask is turned open very cautiously and the solvent is evaporated. The solvent is collected in the cooling traps set up before the oil pump. Evaporation takes up heat of the ambient and so the flask cools down. To prevent the process from ceasing, it's adviced to place a bowl of warm water beneath the flask. The heat taken up before, is released, when the evaporated solvent is cooled down in the traps, thus more liquid nitrogen evaporates then usually. Therefore it's important to watch the filling height of the traps. If a alarge amount of slvent is evaporated, the traps have to be emptied, to avoid cloaking the vacuum line. This procedure is only applicable for substances less volatile than the solvent.

A distillation set up under inert conditions is similar to a regular one, but schlenk-flasks are used, so the flasks can be closed under continuous inert conditions after the distillation. The vacuum access is connected to the schlenk line, and schlenked three times. Hereby a dummy-flask is used, instead of the flask with the mixture. The pieces are put together in inert gas counterflow. It's important to close the valve of the flask, because otherwise the mixture will evaporate into the tube. Now an oil bath can be put under the flask. To control the temperature a thermometer is placed in the bath. If the substance has a very high boiling point the vacuum of the oil-pump is used, for less high boiling substance an additional membrane pump is connected to one of the target flasks. If distilling at ambient pressure the inert gas supply is opened, to avoid excess pressure within the hardware. IF a distillation is made under reduced pressure, it's important to reduce the pressure first und only afterwards heating of the mixture. Otherwise the mixture could evaporate abruptly, spreading all through the distillation hardware. If cooling is applied and stirring in order, the oil bath can be heated slowly.
When the distillation is finished, the targeted flask is connected to the line, the tube is schlenked three times and the flask can be seperated and closed under counterflow.