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Lack of Lewis Catalyst for Bromination (Halogenation)

  1. Feb 24, 2009 #1
    I recently did an organic chem lab in which we brominated acetanilide. Now the benzene group had an acetamido group attached to it, which is less powerful activator than an amide (NH2) group but still directs to the ortho and para positions.

    I can understand that due to steric hindrance, addition in the ortho position would be minimal if not at all. But why is it still that we never used the lewis catalyst during the reaction? could high concentrations of a halogen still cause good yields for halogenation or is there another reason a Lewis acid is not needed?

    Thanks for any help.
     
  2. jcsd
  3. Feb 24, 2009 #2
    Ok after reading and finding some good sources at my schools library, I have come to the conclusion that since we are using a pretty good o,p directing substituent, the bromination although not well will still proceed in the para direction.

    My other question though is that the book I have hear discusses that these bromination usually occur in certain solvents such as acetic acid (glacial), chloroform, and carbon tetrachloride. But does not explain why, could some one help me out here please. my guess is that aqueous solutions, such as water would cause the reaction to be more reactive and thus push for poly-substitution which is not something I desire with the product I want. Is this correct thinking?

    Thanks.
     
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