Use NBS for post-treatment of the bromination reaction.

Related Topics NBS Bromination
Reagents
and Brominated Reactions Recently done bromination, using NBS, CH2Cl2 as a solvent, plus a small amount of ice acetic acid, normal temperature reaction overnight. Then wash with water (the application of dilute hydrochloric acid wash, recently can not buy hydrochloric acid had to use water instead), waterless sodium sulfate
cand
, decompression distillation out of solvent, the resulting solid is orange-red, with petroleum ether wash a few times on the pink, drying color is relatively light, close to white. Do
mass spectrometum
found no target, do not know what went wrong? What do by-products usually do?The literature says to use petroleum ether over the column, but I found that even when dissolved with petroleum ether
heating
to boil, there is still a lot of insoluble (solids about 2 grams, petroleum ether about 300mL), so that can not pass the column ah?analysis: Theis very obvious:1. Either no response, but unlikely!.2. Either according to your description, has been washed away by you! !.3. According to what you call the reaction conditions are unlikely to produce too many by-products!!!the by-product you get may be amber acrylamide, a by-product of NBS. And you want the product should be liquid, you washed away, and you said you over the column insoluble is amber acrylamide you can use dry method on the sample, wet method also does not matter, anyway, amber acrylamide polarity is very large, is not down. Your product polarity is very small.solution:solvent with a dry DMF, add NBS, stir RT. I have done dichlorinated acetic acid system, really produce colored by-products, sodium sulphate washing can not be removed, but can pass the column, dichlorinated petroleum ether 1:1 over. Impurities are on it. And with dmF system is very good treatment, direct reaction to ethyl acetate extraction, sodium sulphate washed off yellow bromine, washing more than 5 times (remove DMF) can obtain pure products.With NBS to do bromination, in the solvent, the reaction is over, first the reaction mixture, with the non-filter
filter
, de-solids, and then the mother liquid washed with water, drying, distillation of the de-solvent can beAfter termination, pour into the water, chloroform extraction,
organic
with saturated NaHCO3 water wash until the color gradually turns pale yellow (generally 2 to 3 times). After drying to remove the solvent, decompression distillation can get the product, the yield is generally more than 80%.
.