Sciencemadness Discussion Board

Bromovanillin Workup?

myristicinaldehyde - 4-2-2018 at 11:28

I found a few procedures that claimed high yielding and quick bromination of phenols and phenol ethers using Oxone, NH4Br in wet methanol- a nicer alternative to using Br2 or HBr! However, I did not have any Oxone but instead boring old persulfate- I gave it a try anyway. I also used NaBr instead of the ammonia salt- NaBr is nicely soluble in the solvent anyway.

The biggest issue is the poor solubility of persulfate: however, if you reflux for 2h you have a mostly clear solution (persulfate gets consumed) The ammonium salt would be preferable.

My issue is isolating the bromovanillin- my first try I just dumped in an equal volume of ice water to the solution, which dissolved the small amount of solids remaining but gave a precipitate too fine to be caught by my filter paper. What little I could get (a gram at most), however, was very much bromovanillin.

Any suggestions for product isolation (other than use finer paper)? Does anyone have any experience with the selective crystallization of bromovanillin from vanillin?

some references:

M. A. Kumar, C. N. Rohitha, S. J. Kulkarni, N. Narender, Synthesis, 2010, 1629-1632.
DOI: 10.1055/s-0029-1218723

N. Naresh, M. A. Kumar, M. M. Reddy, P. Swamy, J. B. Nanubolu, N. Narender, Synthesis, 2013, 45, 1497-1504.
DOI: 10.1055/s-0033-1338431


[Edited on 2018-2-4 by myristicinaldehyde]

Crowfjord - 4-2-2018 at 15:49

Bromovanillin is pretty insoluble in water, while vanillin is fairly soluble. Dilution with water, filtration, and washing with water is typically all that is necessary. It seems persulfate doesn't work well under these conditions. Maybe try modifying the solvent or pH.

Have you read the bromination of vanillin without bromine thread ? I've had good success using the method given by DrNoisez in the third post, substituting the appropriate amount of 16% hydrogen peroxide. There is also an interesting method using sodium bromide and bleach.

DraconicAcid - 4-2-2018 at 16:31

If crystal size is the problem, then don't just dump in water. Maybe slowly add hot water to a hot solution until you get cloudiness, and then very slowly let it cool.