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Topic: Neutralizing an aromatic bromination  (Read 4462 times)

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Offline 1112

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Neutralizing an aromatic bromination
« on: October 04, 2009, 01:11:22 AM »
   I am going to be trying to stop an aromatic bromination (2,5-dihydroxybenzaldehyde, Br2 in CHCl3) with sat. NaHCO3 solution. However, I have been following a WP and I am a little unclear on their procedure. They stated that they stirred the rxn mixture with sat. NaHCO3 solution for twenty minutes. Does anyone know how much NaHCO3 solution I should use (related to mmol Br2 added.... the rxn will be used at larger, and hopefully much larger scales)? There will be layer separation when I pour the NaHCO3 solution into the flask: should I stir fast enough to have the two layers mix (and probably get a very nasty emulsion layer), or should I make sure that separation is maintained?
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Offline Arctic-Nation

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Re: Neutralizing an aromatic bromination
« Reply #1 on: October 04, 2009, 10:32:15 AM »
A good rule of thumb is to start with an amount of bicarbonate solution equivalent to the volume of the reaction mixture and check how it goes. When doing lab-scale experiments relatively little can go wrong, though frothing may occur when a large amount of HBr is present.
I've got another concern, though, and that is that you don't seem to neutralize any excess bromine first. All my brominations were followed by washing with bisulfite or dithionite before any other workup.

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