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Chemistry LibreTexts

Grignards

Quenching Grignards

  1. Remove your RBF from the oil bath, and place it in an ice bath. This tends to make the quench less angry. Leave the condenser on if you have one attached.
  2. Add water, DROPWISE.  Dropwise means dropwise! Be very patient, or you will create a volcano.[1]  Continue adding water until what's in the RBF is no longer angry. Let stir about another five minutes.
  3. Add 10% sulfuric acid, DROPWISE. Again, be patient. Keep adding--very very slowly--until the anger subsides. At this point, I usually let it stir for between 20 minutes and an hour or two, depending on what's convenient.  Give any leftover magnesium and associated salts a chance to dissolve.
  4. Extract into the solvent of your choice (often ether), dry, evaporate, do whatever else is necessary.

[1] Respect the induction period! Generally, it takes several seconds for the Grignard to unleash its wrath upon the water. If you happen to add MORE water during this period, you may end up painting your hood ceiling.