I have refluxed the THF with sodium and benzophenone in an inert atmosphere, this solution turned yellow and should change to a blue color but I do not achieve that result, how long does it normally take, or is there something I am doing wrong?
- Tetrahydrofuran (THF) should be kept overnight with dry potassium hydroxide (KOH) flakes for preliminary drying and to destroy peroxides, that might be present in the sample.
- Only after carrying out the above-mentioned step, THF should be subjected to further drying by refluxing with sodium wire and benzophenone for several hours.
Please note that it is dangerous to add sodium into a solvent, which might contain peroxides. This can give rise to fire / explosion.
THF turns yellow over sodium/benzophenone due to peroxides in the THF. It happens most often if you're using inhibitor (BHT) free THF. To get it you turn blue or purple you can sometimes just add more sodium and benzophenone into the mix, but it typically requires a distillation onto fresh sodium/benzophenone.
- Tetrahydrofuran (THF) should be kept overnight with dry potassium hydroxide (KOH) flakes for preliminary drying and to destroy peroxides, that might be present in the sample.
- Only after carrying out the above-mentioned step, THF should be subjected to further drying by refluxing with sodium wire and benzophenone for several hours.
Please note that it is dangerous to add sodium into a solvent, which might contain peroxides. This can give rise to fire / explosion.
Getting yellow coloration in THF still is a indication that your solvent is not dry. You may need to pre-dry the solvent by Na or NaOH or Molecular sieves and then add to the still. Usually it takes 4-5 grams of sodium and benzophenone each for each litre of THF. Ideally, it should reach purple color after 5-6 hours of reflux but blue color is also usable. Take extreme caution while handling THF stills.
Thanks
- Badges
- Science topic