I am using N-BromoSuccinimide (NBS) to brominate an allylic carbon, I am using CCl4, benzoyl peroxide and light. The starting material disappeared yet no brominated product was obtained, LCMS showed no sign of bromination. Any recommendation?
Dear Nermin Salah, may more details are needed, meanwhile, please check the following links. My Regards
https://www.masterorganicchemistry.com/2011/06/10/reagent-friday-nbs-n-bromo-succinimide/
https://doi.org/10.1021/ja01527a027
https://chem.libretexts.org/Courses/Athabasca_University/Chemistry_350%3A_Organic_Chemistry_I/10%3A_Organohalides/10.03%3A_Preparing_Alkyl_Halides_from_Alkenes%3A_Allylic_Bromination
Hi;
The classical conditions for allylic bromination are the use of NBS in solution in anhydrous CCl4, together with a radical initiator (typically AIBN or benzoyl peroxide). Side reactions can be minimized by recrystallizing the NBS and distilling the CCl4 on P2O5. The peroxide must also be dried on filter paper before use.
With my best regards
I have no lab experience in this but all textbook references just assume NBS magically generates Br2, often showing HBr as a reactant. None of papers or mechanisms show how HBr enters the reaction mixture. Some comments are the Br2 is often in the container with NBS. Likely True. Perhaps alone or with HBr.
I would add a trace of HBr or Br2 to your reaction mixture.
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