myristicinaldehyde
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Mood: сорок пять
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Bromovanillin Workup?
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:
oxone:
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
hbr/bro3
https://blogs.nvcc.edu/alchm/files/2016/05/46_vanillin.pdf
[Edited on 2018-2-4 by myristicinaldehyde]
If we don't study the mistakes of the future we're doomed to repeat them for the first time.
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Crowfjord
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Location: Pacific Northwest
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Mood: Ever so slowly crystallizing...
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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.
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DraconicAcid
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Mood: Semi-victorious.
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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.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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