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5.6C: Troubleshooting Rotary Evaporation

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    1. If the solvent fails to boil on the rotary evaporator even after one minute, consider whether a mistake may have been made. For example, it may be that you are trying to evaporate the aqueous layer from a separatory funnel step instead of the organic layer. Alternatively, the water bath may need to be heated to a higher temperature depending on the boiling point of the solvent.
    2. If droplets are seen among the liquid residue in the flask after evaporation (Figure 5.73), most likely water was not effectively removed from the sample prior to evaporation. To remedy this problem, dissolve the sample is a portion of the previously used solvent, use a drying agent (e.g. anhydrous \(\ce{MgSO_4}\)), filter if necessary, and again evaporate the solvent.
     A: Closeup of receiving flask, showing small pool of clear water in yellow distillate. B: Figure 5.73A with additional zoom.
    Figure 5.73: a) Bubble of water seen amongst an organic liquid after rotary evaporation, b) Zoom-in of the bubble (indicated by the arrow).


    Lisa Nichols (Butte Community College). Organic Chemistry Laboratory Techniques is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. Complete text is available online.

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