zephler
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Registered: 30-10-2010
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NBS to make bromohydrin, DCM extract has Br2 in it?
a bromonation was attempted with NBR, in acetonitrile and H2O - now the technique was a bit sloppy. The reaction mixture was heavily diluted with
water, then extracted with DCM. The DCM was distilled off to re-use again, much to my amazement, the orange colour came over in the distillation of
the DCM - is this Br2? After abut 1 hour, the orange colour completely disappeared! If it is infact Br2 how can I store it (should I just cap up the
DCM and pop it in the freezer?)
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woelen
Super Administrator
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Registered: 20-8-2005
Location: Netherlands
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That orange color indeed must be Br2. Boiling points of Br2 and DCM are not that much separated and when DCM boils over, certainly some Br2 boils over
as well. Disappearance of the color can be explained by assuming that the Br2 reacts with the CH2Cl2 with formation of CHBrCl2 and HBr. I, however, do
not expect this reaction to go fast, unless the mixture is still warm and in full light.
Keeping and storing Br2 dissolved in DCM does not sound like a good idea to me. It will react over time and there is the risk of pressure buildup due
to formation of HBr.
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