monolithic
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Vanillin bisulfite adduct
I recently bought a rather large amount of vanillin. The container it came in isn't very air-tight and I'm concerned about oxidation because I don't
plan on using hundreds of grams any time soon. I want to purify this vanillin and make it stable for long-term storage.
Is there an easy method for preparing the bisulfite adduct of vanillin?
Apparently the adduct of vanillin is water soluble, unlike many other aldehyde bisulfite adducts. This means the usual bisulfite adduct procedure
doesn't work, where the adduct precipitates out as a solid and one simply vacuum filters away the non-aldehyde impurities.
I did some searching and I couldn't find much other than a chemplayer post saying the vanillin adduct is water soluble, and a few inconclusive posts
by Sedit. Maybe form the bisulfite adduct and then wash away the vanillic acid with ethyl acetate? Would this have the intended effect?
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Tsjerk
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See example 1.
Yes, dissolving the vanillin in NaHSO3 and washing it with something apolar should work.
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S.C. Wack
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Solubility has a lot to do with concentration but it makes no sense to purify a nicely crystalline material by converting it to a less nicely
crystalline material...I wonder if it can be extracted from 5% NaOH with e.g. ether.
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monolithic
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Quote: Originally posted by S.C. Wack  | | Solubility has a lot to do with concentration but it makes no sense to purify a nicely crystalline material by converting it to a less nicely
crystalline material...I wonder if it can be extracted from 5% NaOH with e.g. ether. |
| Quote: | | In water >2%; in ethanol is 1:2 vanillin:ethanol. Freely soluble in chloroform, ether, in solutions of fixed alkali hydroxides; solutions in
glycerin and hot water. |
https://pubchem.ncbi.nlm.nih.gov/compound/Vanillin#section=S...
I thought about this too but I'm not sure if it would work. I guess I can try this weekend since I have some NaOH and chloroform on hand. The
advantage of storing it as the bisulfite adduct is that I don't have to worry about it readily oxidizing to the carboxylic acid. 
[Edited on 9-11-2020 by monolithic]
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Pumukli
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Actually, how easily would vanilline be oxidized by air at room temp? Have anyone seen it described in a paper somewhere? Just curious.
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DraconicAcid
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| Quote: Originally posted by S.C. Wack | | Solubility has a lot to do with concentration but it makes no sense to purify a nicely crystalline material by converting it to a less nicely
crystalline material...I wonder if it can be extracted from 5% NaOH with e.g. ether. |
Vanillin is a phenol, and will form a phenoxide in NaOH.
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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Boffis
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Vanillin is very resistant to oxidation under any conditions. It seems that the more complex hydroxyaldehydes are resistant for some reason.
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monolithic
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| Quote: Originally posted by Boffis | | Vanillin is very resistant to oxidation under any conditions. It seems that the more complex hydroxyaldehydes are resistant for some reason.
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I did not know that, I assumed it readily oxidized.
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Sedit
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| Quote: Originally posted by monolithic |
I did some searching and I couldn't find much other than a chemplayer post saying the vanillin adduct is water soluble, and a few inconclusive posts
by Sedit. Maybe form the bisulfite adduct and then wash away the vanillic acid with ethyl acetate? Would this have the intended effect?
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I have almost always had issues trying to form Bisulfite Adducts with stuff like this Monolithic. I do vaguely remember it being rather water soluble
but no matter what I did strong Vanillin smells remained suggesting formation was problematic and recovery from the adduct to test how well it worked
was also plagued with problems. It is likely just me but personally I hate attempting to form Adducts at all. Unstable, unreliable and simply have
always been a thorn in my side.
3/10 Would not recommend.
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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Metacelsus
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The odor threshold for vanillin is very low, so it will smell strongly if even traces are left.
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