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16.11 Extractions and Distillations

Extractions

  • Do not attempt to extract a solution until it is cooler than the boiling point of the extractant due to the risk of overpressurization, which could cause the vessel to burst. 
  • When a volatile solvent is used, the solution should be swirled and vented repeatedly to reduce pressure before separation. 
  • When opening the stopcock, your hand should keep the plug firmly in place. 
  • The stopcock should be lubricated. 
  • Vent funnels away from ignition sources and people, preferably into a hood. 
  • Keep volumes small to reduce the risk of overpressure and if large volumes are needed, break them up into smaller batches.

Distillations

  • Avoid bumping (sudden boiling) since the force can break apart the apparatus and result in splashes. Bumping can be avoided by even heating, such as using a heat mantle. Also, stirring can prevent bumping. Boiling stones can be used only if the process is at atmospheric pressure.
  • Do not add solid items such as boiling stones to liquid that is near boiling since it may result in the liquid boiling over spontaneously. 
  • Organic compounds should never be allowed to boil to dryness unless they are known to be free of peroxides, which can result in an explosion hazard.

Reduced pressure distillation

  • Do not overheat the liquid. Superheating can result in decomposition and uncontrolled reactions.
  • Superheating and bumping often occur at reduced pressures so it is especially important to abide by the previous point on bumping and to ensure even, controlled heating. Inserting a nitrogen bleed tube may help alleviate this issue. 
  • Evacuate the assembly gradually to minimize bumping. 
  • Allow the system to cool and then slowly bleed in air. Air can cause an explosion in a hot system (pure nitrogen is preferable to air for cooling). 
  • See “reduced pressure” for vacuum conditions.