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Chemistry Forums for Students => Organic Chemistry Forum => Organic Chemistry Forum for Graduate Students and Professionals => Topic started by: Babcock_Hall on October 05, 2021, 10:00:23 AM

Title: Bromination of an aromatic ring during dibromination of an acrylamide
Post by: Babcock_Hall on October 05, 2021, 10:00:23 AM

“Asymmetric unbridged nitrogen. 37. Absolute configuration of diastereomeric derivatives of N-substituted aziridine-2-carboxylic acids,” Eremeev, A. V. et al., Khimiya Geterotsiklicheskikh Soedinenii, (10), 1343-8; 1984.
https://scifinder.cas.org/scifinder/view/link_v1/reaction.html?l=T5OKcO0Ri0Vxs5SgbYOjGm26-6iGYSw8UlFRbBHz68R_vVhlq9BAfimSHxiQW4MT

I would like to dibrominate the double bond of N-phenylacrylamide.  I turned up the reference above but I have not obtained it yet.  This paper indicated that the aromatic ring would also brominate at the 4-position (76%) yield.  I don't know the conditions of this reaction yet.  Other compounds, some of which bear both a phenyl and a methyl group on nitrogen, were able to undergo dibromination of the double bond without attack on the ring.  One reagent that was used was a combination of LiBr and NaIO₄.

I also glanced at the amines chapter in David Klein's textbook.  Two of the entries in this chapter indicated that having an amide will lead to fewer brominations of an aromatic ring than an amine would undergo, but that the 4-position was still a point of bromination.  I would prefer not to brominate the ring, but I can live with it if I have to.  If the dibromination of the double bond is much faster than bromination of the aromatic ring, I might be able to obtain the desired product, as long as I control stoichiometry.  Thoughts on best conditions?

Title: Re: Bromination of an aromatic ring during dibromination of an acrylamide
Post by: sjb on October 05, 2021, 12:58:07 PM

Link that doesn't need Scifinder - http://dx.doi.org/10.1007/BF00503598

Title: Re: Bromination of an aromatic ring during dibromination of an acrylamide
Post by: Babcock_Hall on October 05, 2021, 02:12:05 PM

Thank you; that is very helpful.  How did you find that link? 

There was a 1.5 mole to mole ratio of bromine over the anilide.  Having already purchased the starting material, I think that I will live with bromination of the aromatic ring.  If I want to avoid bromine on the ring, it may be possible to make N-phenylacrylamide from 2,3-dibromopropionic acid, aniline, and SO₂Cl, based on the chemistry of similar compounds.

Title: Re: Bromination of an aromatic ring during dibromination of an acrylamide
Post by: rolnor on October 06, 2021, 02:12:19 AM

It seems very convenient to use the 2,3-dibromo acid and aniline. It can be a problem to separate non-brominated and brominated material if you get partial 4-bromination of the ring.