Rotary evaporators (also called "rotavaps") are used to remove solvents from reaction mixtures. We have two systems in our lab and others are available to us when not being used in the teaching labs. Our systems have water baths that are used to keep the solvent in the reaction flask from freezing during the evaporation process (remember your P-Chem!). The solvent is removed under vacuum, is trapped by a dry-ice condenser, and is collected for reuse (rarely) or disposal (usually). Note: the rotovaps are not to be used for air and/or water-sensitive materials - we use the trap-to-trap system on the Schlenk lines for those situations. Our systems are hooked up to vacuum pumps capable of producing a range of desired pressures (i.e. we can control how much vacuum is used). The fact that a vacuum is applied means that the boiling points of the solvents are going to be significantly lower than at ambient pressure. As a guide, see the table below for some common solvents and their bioling points under reduced pressures. Since the flask is also rotated during the evaporation process, the surface area is larger than normal which also increases the evaporation rate significantly.

If at any time you notice an error on this page or if you have any questions, please contact Dr. Daley.

Rotovap Solvent Reference (Temperature in degree C)*

Solvent	b.p. (760 torr)	b.p. (40 torr)	b.p. (10 torr)
Acetone	56	-14	-35
Acetonitrile	82	8	-15
Diethyl ether	35	-28	-55
Ethanol	78	19	-6
Ethyl acetate	77	9	-14
Hexanes	69	-2	-26
Methanol	65	5	-17
Toluene	110	30	4
Water	100	34	13

* Values at 10 torr calculated using heat of evaporation data and web-based calculator.

General rules for usage of rotary evaporators. See pictures of Rotovap #1 and #2 on right for reference to labels in the instructions below.

1. Make sure all joints are clean and free of any particulate (grit, sand) as the latter will crack the glassware. Do not grease the bump trap joints nor the joint of the flask you are removing the solvent from as you do not want grease impuritites to fall into your flask on dissolving in the liquid-vapor of your solvent.

2. The solvent collection flask (labeled F1) of the unit should always be emptied before/after use to prevent accidentally mixing of incompatible chemicals. SAFETY FIRST!

3. Make sure the system is in the proper starting setting. The glass stopcock valve (labeled V1 on picture to the right) at the top of the evaporator should be open to the vacuum pump. The glass stopcock valve (labeled V2) on the lower left side of the condensor should be open to the atmosphere. The arm of the evaporator should be at it highest position setting (i.e. the arm is as high as it can go above the water bath) - use the controller (labeled C1) to raise/lower the arm. The solvent receiving flask (F1) is attached to the condenser using grease on the joint (only a small amount is needed) and secured in place with the metal clamp. The appropriate sized bump trap should be on the evaporator (use bump trap that has correct size adaptor for your flask) and held there with a Keck clip (green clips fit 24/40 ground glass joints, blue clips fit 19/22 joints, and the yellow ones fit 14/20 joints). The condensor is filled with dry ice/isopropyl alcohol. The alchol should be added first, to a level about 1 inch above the section where the inner trap narrows to a cone-base (see red arrow on picture). Slowly add small pieces of dry ice to the alcohol (it will splash when adding so make sure the pieces are small and wiat until solution calms down before adding new pieces) until limited splashing/bubbling occurs and then add larger chunks until the trap is 3/4 full with dry ice making sure the pieces are not wedged to the sides. Note - the dry ice will be stacked above the alcohol level but it will fall once the lower portions in the solution are consumed. The water bath is filled to within about an inch of the top using only DI water.

4. Place the flask with the solution to be evaporated on the bump trap of the rotary evaporator. The use of a bump trap prevents the solution from accidentally splashing into the condenser (and being contaminated). Start with a clean bump bulb in case something bumps over after all! This would allow the experimenter to recover the solution or solid. Note: your flask cannot be more than 1/2 full of solution as the odds of bumping will be significant and it will result in a loss of product not to mention a waste of time and a lot of cleaning.

5. Use a Keck clip to secure the flask to the bump trap.

6. Start the rotation of the flask by turning the appropriate dial (labeled S1). Start at a low-medium rate to ensure the flask rotates smoothly (not wobbling) and the solution flows nicely. Slowly increase the rate to a maximum where the solution flows well and does not get too close to the neck of the flask..

7. Turn on the vacuum pump (located on left side of rotary evaporator - under the shelf). The on button is at the bottom and should turn green when starting. Make sure the vacuum dial is turned to the fully open position (counter-clockwise) so as not to immediately start with a high vacuum when the pump is turned on (even though the rotary evaporator valve should be open to the atmosphere to start and thus it should be fine).

8. Close the valve (V2) to place system under vacuum. Slowly increase the vacuum (i.e. lower the pressure) by turning the dial clockwise on the vacuum pump (labeled P1) while keeping you hand on the valve V2 being ready to open it to the atmosphere in case of bumping. If you get the pressure to about X (see dial on the vacuum pump) without any bumping, continue on to the next step.

9. The flask is lowered into the water bath, which is set to the appropriate temperature for the solvent you are removing. See the table above to chose an appropriate bath temperature. Note: the lowest temperature set the bath to is 25 degrees Celcius. For Rotovap #1 you set the temperature using the dial on the water bath (T1) and the reading is displaded digitally above it (when you turn the dial the display will change to show the value you are setting the temperature to and when you stop moving the dial the display will return to value of the actual water bath temperature). For Rotovap #2 the temperature is set using the control panel and is displayed there as well.

10. The solvent should start collecting on the condenser and drip into the receiving flask (F1). Some solvents (such as diethyl ether or dichloromethane) are so volatile that they will also evaporate from the receiving flask and be discharged into the pump! To prevent this, use a lower vacuum setting (higher pressure) and lower heat setting on the water bath.

11. Once all the solvent has evaporated (or whatever you have reduced to volume of solution to your desired point), release the vacuum by opening the V2 valve to air and then turning the dial on the vacuum pump counter-clockwise until is is wide open. The flask is then raised out of the water bath and the spinning is discontinued. Turn off the pump but note that the pump will remain on with the light changing to "red". The pump undergoes a "self-cleaning" process, which takes a minute or two, and then it will shut off on its own.

12. Remove your flask and store it in a safe spot (usually on a corkring with a plastic cap used to cover opening of flask) then empty the receiving flask contents into the waste bottle, clean it and the bump trap as necessary, and the return the receiving flask to the evaporator making sure the joint is clean and freshly greased (do not go crazy on the grease) before attaching it and securing it with the metal clamp.

Maintenance Notes:

Distilled water should be used in the heating bath to minimize the scale build up in the bath which coats the thermistor. It is very difficult to remove and reduces the efficiency of the bath. In addition, regular tap water will promote the growth of spectacularly disgusting algae colonies, particularly during the summer months. The best protocol is a regular exchange of the water.

To remove algae gunk from the inside of a coiled water condenser, the condenser has to be removed from the rotavap and the coil is soaked in a dilute nitric acid solution for a few hours (only done in the presence of Dr. Daley). After carefully rinsing the insides, the rotavap is reassembled. All standard safety precautions should be followed when working with nitric acid!

The ground glass joint holding the flask does not need to be greased, but on rare occasions it (or the bump bulb) may get "frozen". Do not try to remove the flask by yourself! Get Dr. Daley and he will remove the flask. When "frozen", there is a very high chance that the flask will break and thus cuts, etc. can easily occur so do not try to do it yourself.

If something is not working properly, please tell Dr. Daley as soon as possible so that ideally the issue can be resolved quickly and easily. Left unaddressed, the problem could result in a catastrophic fail, which will cost a significant amount of time and money so lets not do that.