Safety Emporium for all your lab and safety needs
Safety Emporium for all your lab and safety needs

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Rotary Evaporators



Rotary evaporators (also called "rotavaps" in lab slang, ) are used to remove solvents from reaction mixtures and can accommodate volumes as large as 3 liters. They are found in almost every organic laboratory.

A typical rotary evaporator has a heatable water bath to keep the solvent from cooling or even freezing during the evaporation process. The solvent is removed under vacuum, is trapped by a condenser and is collected for easy reuse or disposal. Most labs use a simple water aspirator vacuum on their rotavaps, so a rotavap can not be used for air and water-sensitive materials unless special precautions are taken.

Shown below on the left is a Büchi rotary evaporator available through Fisher Scientific. The one shown on the right is not as modern but has the same exact functionalities.

a rotavapand another

Using a rotary evaporator

  1. Empty and then replace the solvent collection flask on the unit. SAFETY FIRST! You don't want to accidentally mix incompatible chemicals.

  2. Place your flask on the rotary evaporator. Most people use a bump bulb to prevent their material from accidentally splashing into the condenser (and being contaminated). Always start with a clean bump bulb! Our personal favorites are the CG-1319 (top, left) and CG-1323 (bottom, middle):

    Click on any bump bulb below for more information or to purchase

    Bump trap
    Bump Trap
    Bump Trap
    Bump Trap
    Bump Trap
    Bump Trap w/
    Drain Holes
    Bump trap
    Bump Trap
    Upper Vapor Tube
    Bump Trap
    Bump Trap
    Fritted Disc
  3. Use a metal or Keck clip to secure your flask and your bump bulb. The green one shown below fits 24/40 ground glass joints. Similar blue clips fit 19/22 joints and the yellow ones fit 14/20 joints.

    a green clip

  4. Use the speed control to rotate the flask. A typical rotavap uses a variable speed sparkless induction motor that spins at 0- 220 rpm and provides high constant torque.

  5. Turn on the aspirator vacuum. On most models, the vacuum on/off control is managed by turning a stopcock at the top of the condenser (left side of the above diagram).

  6. Lower your flask into the water bath. On most models, a convenient handle (with height locking mechanism) moves the entire condenser/motor/flask assembly up and down. You can also adjust the tilt of the condenser assembly. Be sure not to put the flask into a water bath that exceeds the boiling point of your solvent!! For small amounts of common solvents you don't need to turn on the bath heater.

  7. The solvent should start collecting on the condenser and drip into the receiving flask. Some solvents (such as ether or methylene chloride) are so volatile that they will also evaporate from the receiving flask and be discharged down the drain. To prevent this you can place a cooling bath on the receiver or (on some models) use a dry ice condenser.

  8. Once all your solvent has evaporated, release the vacuum, raise the flask out of the water bath and turn off the rotation. Remove your flask and enjoy.

  9. Be sure to clean the bumb bulb and empty the receiving flask when you are done.

Tips and Tricks

book cover

Purification of Laboratory Chemicals is one of many books and pamphlets you'll find at Safety Emporium.


This page was last updated Sunday, June 12, 2016.
This document and associated figures are copyright 1996-2016 by Rob Toreki. Send comments, kudos and suggestions to us via email.