-Tried using anhydrous chloroform
-Tried both NBS and recrystallized NBS (though, the recrystallized NBS has a slight yellow tinge for some reason)
-The procedure I've been following for the most part is to heat the reaction to 60C. I've monitored it by TLC to completion, but I'm getting incredibly low yields.
-I've tried letting it run a room temperature for about 24h, and still had low yields.
Was there a preservative in the anhydrous chloroform? If it was amylene or cyclopentene these can react with NBS. These stabilizers are typically present at levels of 100ppm or greater and could be using up most of the NBS. I used chloroform preserved with ethanol that I ran over an anhydrous alumina column immediately before use in NBS reactions.
ah, I see. I'll have to check next time I'm in the lab and keep that in mind. Thanks!
Try to add 3 or 4 eq of solid Carbonate sodium or potassium anhydrous (it will not dissolve but I think it will help to reduce the eventual side effects of an acidic medium). Filter it at the end of the reaction and proceed as before.
Good luck
Without knowing a bit more about the structure of your pyrrolopyrrole it's difficult to say what the problem might be. Asssuming you are brominating the ring, you might want to try either acetonitrile or DMF as solvents as these are often more effective. Also NBS is quite a bulky reagent so steric crowding might be a problem, in which case you could try bromine/sodium acetate as the brominating agent.
Take distilled chloroform, NBS and some radical initiator azobisisobutyronitrile (AIBN) or benzoyl peroxide. Usually NBS is a radical type brominating agent, so you need radical souurce. Irradiation might also help. Tetrachloromethane (CCl4) is a best solvent for NBS bromination but it is carcinogenic.
Sorry! I forgot to mention that there are thiophene units on both sides of the molecule. The thiophene moieties are what I am trying to brominate. Thank you very much for all the suggestions thus far, everybody.
You may try the reaction by changing solvent from chloroform to ccl4. Reaction is photochemical and should proceed at 60 to 70 degree. The product may need column filtration.
Dear all,
im trying to do the bromination of indole and i want 3 bromoindole as my product ..kindly help
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