I have been trying a Bromination reaction using the reported method of Bromine in Acetic Acid (addition at 0 degrees followed by refluxing). The procedure reports that a white insoluble solid will be formed which can be filtered off easily. I have tried that about 3 times and no insoluble solid was obtained. The resulting solution which I got was subjected to concentration and crude NMR and LC-MS analysis reveals that my desired compound was not formed. In one attempt, I got back unreacted starting material but in all other cases, NMR revealed that desired compound was not formed and starting material was not present. I have also tried another method using LDA and 1,2-dibromoethane but even that was not successful. Work-up followed by crude NMR and TLC analysis revealed that the starting material was consumed but the formed compound was not the desired compound.
Arnab Biswas in order to get an idea what might have gone wrong, it would be helpful if you could provide the reference in which the synthetic procedure is described. I will then have a look at it.
Hi Arnab,
It might be worth trying with NBS (1.2 eq) in THF. Start at RT and and heat if needed.
Best P
Arnab Biswas I fully agree with Patrick Killoran and Nadim Shaikh in that bromination using NBS should be worth a try. For more information please check out the following reference:
Article A novel method for the bromination of thiophenes
Hi there,
Are you sure bromine is not escaping as gas during reflux? Are you doing the reaction in a closed system?
I am not sure about the possible side reactions of NBS in presence of an amide group.
Dear Arnab Biswas and Vijayakumar Samiyappan if you work with NBS there is no free bromine which could escape. I would not worry about possible side reactions and just give it a try!
Dear Frank T. Edelmann Thanks for your comment.
I was thinking about what could gone wrong in Br in AcOH, in that case there is a possibility of Br2 evolution and escape if it's not a closed system.
It's true that no need to worry about Br evolution when using NBS since it's following radical pathway and we can try.
Dear Vijayakumar Samiyappan please see this useful link about bromination reactions under reflux conditions:
https://chemistry.stackexchange.com/questions/139666/safest-way-to-conduct-a-reaction-with-bromine-under-reflux-conditions
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