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Roto-evaporation Cheat Sheet by

Roto-evaporation process explained
chemistry     procedure     roto-evaporation

Introd­uction

A rotary evaporator is a device used in chemical labora­tories for the efficient and gentle removal of solvents from samples by evapor­ation.

Rotary evapor­ators are also used in molecular cooking for the prepar­ation of distil­lates and extracts.

Roto-e­vap­oration requires mechanical rotation of a flask under vacuum. The rotation of the flask increases the surface area of the solvent to be removed, increasing the rate of evapor­ation, and reducing the risk of "­bum­pin­g": when a large pocket of solvent vapor forms rapidly and displaces the surrou­nding liquid. The vacuum reduces the boiling point of the solvent, as well as providing a means to separate the solvent from the compound of interest.

1. Setup

Pour the mixture of solvent and desired compound in a round bottom flask. Best results are achieved when the flask is filled less than half full of the solution.
Fill the rotovap cold traps with dry ice.
Attach a glass "bump trap" which prevents any solution from entering the main part of the rotovap. Secure with a Keck clip.
With a Keck clip attach the flask and bump trap to the adapter portion of the roto-e­vap­orator.
Lower the flask into the water bath. This helps to prevent the flask from discon­nec­tion.

2. Rotary Evaporator Operation

Start the rotation. Different speeds are preferable for different volumes.
Slowly start increasing the vacuum. The vacuum is at the proper strength when: 1) conden­sation of the solvent can be seen on the cold finger or in the receiving flask, or 2) the solvent begins to bubble.
Turn on the heat for the water bath. Recall from general chemistry that vacuum reduces the boiling point of the solvent, so signif­icantly lower temper­ature is needed to evaporate the solvent using a rotovap than at STP.
Adjust the vacuum setting as needed.
When all solvent has been removed turn off the vacuum and return the flask to atmosp­heric pressure.
Stop the rotation.
Raise the flask from the bath.
Remove the flask from the adapter.
If there is more solvent to remove it can be added it to the same flask and the procedure is repeated. Remember to empty the receiving flask when the evapor­ation is complete.
 

Rotary Evaporator

The main components are

1. A motor unit that rotates the evapor­ation flask or vial containing the user's sample.
2. A vapor duct that is the axis for sample rotation, and is a vacuum­-tight conduit for the vapor being drawn off the sample.
3. A vacuum system, to substa­ntially reduce the pressure within the evaporator system.
4. A heated fluid bath (generally water) to heat the sample.
5. A condenser with either a coil passing coolant, or a "cold finger­" into which coolant mixtures such as dry ice and acetone are placed.
6. A conden­sat­e-c­oll­ecting flask at the bottom of the condenser, to catch the distilling solvent after it re-con­denses.
7. A mechanical or motorized mechanism to quickly lift the evapor­ation flask from the heating bath.

Rotary Evaporator Video

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