Problems in the NBS bromide methyl reaction.

-related topics NBS brominated

reagents and brominated reaction I reacted from the raw material is that the benzene ring pair is a methyl and positive hexaEther bond, NBS bromide, BPO as the trigger, carbon tetrachloride as a reaction solvent, the target product should be the left of the methyl there on a bromine. Doing it many times is not successful.several times: perhaps NBS was added too quickly, resulting in two bromides, then hydrolysed into two hydroxyls and turned into aldehyde., the increase reflects the nitrogen atmosphere, isolating the air, and the result is the same., add NBS in batches, my God, the result can still drive people crazy.don't know what went wrong. Solvent carbon tetrachloride is bought 500ml analysis pure, no re-steaming, this should not affect so large.ask you to help, has studied three, help ah, save a life, win the seven-level butcher.answer: the first two Br is inevitable, how many questions. You can try to recrystrystry. For example, EA/PE systemor directly with ether low-temperature recrystallization to try, I have used these two systems are very good.second is: solvent add more points, and then BPO first add, NBS in 65 degrees or so in batches to add, slow down point. After the addition, the reflow reaction. This may be less than the last two.is or change AIBN try, this trigger trigger temperature will be a little lower, generally about 40 degrees can trigger.recommendations are as follows: 1, NBS: product feed 1:1 2, plus NBS, the drug spoon added in batches.be in an ice bath, or in a cold well, when you add 3 or NBS.4, add NBS, ice bath reaction 1H or so, and then move to room temperature reaction, at any time point plate detection !!!!5, with AIBN 6, change the solvent, ether or tethydrofuran 7, the NBS into a four-hydrogen furan solution drop 8, NBS equivalent at 1.0 is good, more is no use<2>9, this reaction is done, the yield does not exceed 70to improve the yield, the NBS into bromine, reaction in tyhydrofuran, temperature does not exceed 15 degrees, bromine equivalent in about 1.2, the main impurities for the first two and did not complete the reaction of raw materials. It would be good to crystallize with toluene or EA / PE. When I was doing it, the substrate was slightly different, the solvent was 4-methyl tethydrofuran, after the reaction was completed, the product was directly presumed,
filtration
can be, and then purified with toluene crystallization.
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