7.23: Vacuum Distillation
- Page ID
- 97227
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Always use a stir bar, not boiling stones. Grease all joints. Use a Claisen adapter, as solutions tend to bump under vacuum. Connect thick-walled hosing at the vacuum adapter to a trap, then to the vacuum source (water aspirator or vacuum pump). |
Turn on the vacuum first, before heating, to remove very volatile components. When confident the apparatus is maintaining a reduced pressure, then heat the sample. Use glass wool or foil insulation if the sample is stubbornly refluxing instead of distilling. |
Record the temperature and pressure if using a manometer during active distillation. Pure compounds may not distill over a constant temperature due to changes in pressure. If multiple fractions will be collected, the system needs to be vented and cooled in between (or a cow receiving flask used). |
To stop the distillation, remove the heat and cool the flask in a tap water bath. Then open the apparatus to the atmosphere by opening the pinch clamp on the trap, or removing the tubing on the vacuum adapter. Lastly turn off the vacuum. Correct order: cool, open to atmosphere, then turn off vacuum. |