In organic chemistry, we often need to remove solvents from solutes in order to collect products.
Once the solvent served its purpose we can get rid of it to continue the analysis of the solute.
To separate volatile solvents from non-volatile solutes we can use an extraction technique called rotary evaporation (a fancy distillation).
We usually use rotary evaporation in: liquid-liquid extraction techniques, chromatography fractions and in crude reaction mixtures.
What is a Rotary Evaporator? – Definition
Rotary evaporators represent devices used in chemical laboratories to remove solvents from solutes through evaporation.
Main components of a rotary evaporator
1. Boiling flask
The boiling flask is used to heat volatile materials and drive them into the vapor phase.
2. Condenser
The condenser is used to create an actively cooled region of glassware intended to condense the vapor back into a liquid.
3. Receiving flask
The receiving flask is located in a different area of the device, and is used to accumulate condensed liquid that is kept separated from the original sample.
4. Rotation unit
The rotation unit is a motor that spins the boiling flask along the axis that goes through the opening.
5. Elevation rail
The elevation rail is used to slide the entire system up and down to put it into or raise it out of the bath.
6. Dimroth condenser
A dimroth condenser is a spiral condenser inside of the glassware used to create a large amount of cold surface area (a very efficient condenser).
7. Ports
Ports to attach a vacuum line and ports for water lines are used to cool the condenser.
8. Solvent trap
The solvent trap is used for catching and trapping the solvent.
9. Warm water bath
The warm water bath is used to encourage evaporation in the boiling flask.
10. Ice bath
The tole of the ice bath is to discourage evaporation once the solvent starts accumulating in the trap.
11. Bump trap
The bump trap located between the boiling task and the stem of the rotation unit is actually a small bubble of glass designed to catch the liquid and prevent it from draining back into the boiling flask to contaminate the material that we’re trying to isolate.
12. Clips
Clips are used to hold the solvent trap and the boiling flask in place.
13. Controls
Controls are used for rotation and temperature.
How to Use a Rotary Evaporator?
Before starting to use the rotary evaporator, we need to inspect all the glassware that will be used such as: the condenser, the solvent trap, the boiling flask and the stem of the rotation unit for any irregularities like cracks, stars or chips because any defects of the glass will affect the entire process and could even cause in implosion.
If the device has no issues and is clean, we are ready to start the work.
Step one
We start by running cold water to the Dimroth condenser to create a zone of cooling in the condenser.
We can add some ice to the bath around the solvent trap to be sure that we accumulate as much solvent as possible in the liquid phase without allowing the liquid to vaporize back into the system.
Step two
We continue by clipping the boiling flask in place with the sample inside of the flask.
We are using the clip to hold the flask in place before starting the rotation.
The rotation will spread some of the solvent out along the interior walls of the flask to promote evaporation, and will also add the sample slightly, which will reduce the risk of bumping or flash boiling the sample that could cause solvent contamination or otherwise adversely affect the entire process.
Step three
In the third step, we will slowly evacuate the system by opening the vacuum line.
While we open the vacuum line, the sample will be agitated and will have a reduced pressure, which means that the boiling points of all the volatile materials have been reduced.
Step four
In the next step, we need to apply heat to the boiling flask to make all the volatile materials go into the vapor phase.
Step five
In the final phase, we can see that the volatile solvent materials are vaporizing while moving up the stem and condensing on the Dimroth condenser.
From there, the liquid drains into the solvent trap and stops only when we’ve exhausted all the solvent from our sample.
At this point, we have managed to successfully isolated the volatile material from the non-volatile material.
Conclusion
This is how rotary evaporation actually works.
More info about these devices is provided by Engineeringk12 where you can find a complex list of rotovaps (rotary evaporators) with reviews for each model.
