According this scheme the bromine act as a nucleophile and attacks pyrimidinium generating Br+ species? I always thought that Br2 acts solely as electrophile with Br- as by product.

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  • $\begingroup$ I agree it doesn't look right. Perhaps there is an initiation step where $\mathrm{Br^-}$ is created for example by attack of $\ce{SO_3^-}$ on bromine. $\endgroup$
    – K_P
    Oct 4, 2015 at 17:04
  • $\begingroup$ @K_P Only there's no $\ce{SO3-}$ in there, only $\ce{SO3}$ (gas) and $\ce{HSO4-}$. $\endgroup$
    – Jan
    Oct 4, 2015 at 17:36
  • 2
    $\begingroup$ @Jan I meant from the pyridinium suflonate that is formed but it was an example. One could think other ways to create some $\ce{Br^-}$ to initiate the reaction. And in any case it is just a suggestion. $\endgroup$
    – K_P
    Oct 4, 2015 at 17:51


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