The rotary evaporator is an instrument that is designed to allow you to distill a liquid under conditions of reduced pressure. Since the pressure within the system has been reduced, that means that the liquid can now distill at a lower temperature than it would at atmospheric pressure. This is a very safe and fast method of distilling flammable solvents. However our system will only work for solvents that would normally boil at temperatures less than 60°C at atmospheric pressure.

The rotovap itself consists of the following parts:

a) a long condenser containing a distillation tube surrounded by a coil of glass tubing. This glass tubing will have cold water running through it to provide a cooling atmosphere for the gas as it is being distilled. (left)

b) The condenser is hooked up to a water aspirator which will allow you to evacuate the system. To close the system and thus activate the vacuum, turn the stopcock knob at the far end of the rotovap to align it with the vacuum (ie. turn until the arrow on the knob points straight down towards the attached tubing ie. knob is pointing to the “ON” position). The system is now under reduced pressure. (below)

c) A large round collection flask is attached to the condenser to collect the distillate when it forms. (left)

e) A rotary dial is included that will allow you to spin the sample flask (left)

USING THE ROTOEVAPORATOR

1. Add your sample to be rotovapped into the RB flask. NOTE: your RB flask should never be more than half full with liquid when you attach it to the rotovap. If it is, you risk losing some of your sample! If you have too much liquid to evaporate, remove some until the flask is less than half full, rotovap away the liquid in the RB and then add the rest. Or you can use a hot water bath in the fumehood to boil away some of the excess solvent.

Correct (left)                   Incorrect (right)

3. To close the system and thus activate the vacuum, turn the stopcock knob at the far end of the rotovap to align it with the vacuum (ie. turn until the arrow on the knob points straight down towards the attached tubing ie. knob is pointing to the “ON” position). The system is now under reduced pressure.


4. The liquid in the RB flask can now boil at a lower temperature. However, you can speed up the evaporation by rotating the flask, which throws up more liquid on the walls of the flask and thus increases the surface area for evaporation. As long as your flask is less than half full, you can turn the rotary dial on the front of the instrument as far as it will go to obtain maximum spin. If the flask is more than half full, then reduce the speed.

5. To also speed up the rate of evaporation, the liquid sample can be warmed with hot water. Raise the hot water bath until the hot water covers the liquid level in the RB flask. If the RB flask is more than half full, bring the water bath up until the water just touches the bottom of the RB flask; as the liquid evaporates, the flask can then be further immersed in the bath.

6. As the solvent evaporates, its vapour will go up the trap into the distillation tube and exit about halfway up the condenser coils. These coils are filled with cold water and thus the hot gas will condense there. Very soon, you should notice liquid dripping off the coils and collecting in the large condensate flask below the coils.

NOTE: sometimes when you have a very small volume, you may not notice any dripping from the condenser coils. If this happens, wait 1-2 minutes and observe if there is any change in the RB flask. When the dripping stops or you don’t notice any dripping off the coils for at least 30 seconds, you can stop the rotovap. You do this in the reverse order from the way you started:
(i) lower the hot water bath so that it is not touching the RB flask and there is enough clearance so that you will be able to safely remove the flask.
(ii) turn the rotary dial to stop the spinning of the flask.
(iii) turn the stopcock knob up to the “OFF” position to release the vacuum.
(iv) remove the blue clip from the flask. It is usually easier to do this if you turn the clip to the back away from you, place your right hand around the RB and your right thumb on the nearest handle of the blue clip while grasping the opposite handle with your left hand. Push back on the two handles and the clip should come off. Place your left hand on the trap and with your right hand, slowly twist the neck of the RB flask to break the vacuum. DO NOT REMOVE the flask by pulling straight downwards; this can result in a loss of some of your sample in the RB flask. Leave your flask uncorked at this stage.