USING A ROTARY EVAPORATOR

The rotary evaporator provides a means of removing large volumes of solvent from solution under mild conditions.
It uses reduced pressure so the solvent evaporation temperature required are much lower than those required at atmospheric pressure.
All the apparatus looks complex. Its operation is quite straight forward.
To start, turn on the water supply to this mild condenser.
Next, turn on the water vacuum pump.
Make sure the pressure release verve at the top of the condenser is open.
Notice that the vacuum line is fitted with a trap to prevent water from sucking back.

The sample should be placed in a round bottom flask and should never more than half fill the flask.
Slide the flask unto the ground glass joint and clip it in place.
The joint should not be greased.
Then switch the motor on so that the flask rotates at a moderate pace.
Close the pressure release valve.
Wait about 20seconds while the vacuum builds up.
Then lower the flask into the water bath.
 On this apparatus, the stop on the column is preset so that the flask descends to the correct level.
In some set-up, the water bath is raised to the flask.
Either way, the water level must be no higher than the level of solution in the flask.

Set the temperature of the water bath to give a steady rate of solvent evaporation.
This can be judged by the rate at which condensed solvent trickles out of the condenser into the receiver.
If the rate of solvent removal slows down, increase the water bath temperature.
Should the rate of evaporation become too high, froth may occur.
It can be controlled by briefly opening and closing the pressure release valve.

When most of the solvent has been removed, the product may line the wall of the flask as a solid but often an oil is formed.
Lift the flask from the bath.
Stop the rotation.
Turn off the water bath so it doesn’t boil dry.
Release the vacuum and allow the flask to cool until it can be comfortably handled.
Remove the flask
Place it on a cork ring and stopperd it lightly
Then remove the solvent receiver and empty the content into the appropriate waste solvent container.
Having turned off the cooling water, replace the solvent receiver so that it is out of harm’s way.

Finally, clean up the ground glass joint ready for the next user.
At the end of this procedure, it may be necessary to further purify the product by re-crystallization or distillation.