Metacelsus
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Column chromatography of acid-sensitive compounds
I am currently trying to prepare a compound of the type shown below:
I can make it just fine, but purifying it is annoying because it slowly decomposes in contact with silica gel. The main decomposition product is
catechol carbonate.
I've heard adding 1% triethylamine to the eluent (which is 10% ethyl acetate in hexanes) might help. Alternatively, switching to alumina instead of
silica could work. However, I don't have alumina TLC plates so I can't do TLC using alumina. Distillation and crystallization are out of the question,
since the compound is a liquid that is also sensitive to heat.
Does anyone here have experience with purifying acid-sensitive compounds by chromatography? What do you think I should do?
[Edited on 3-17-2018 by Metacelsus]
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DraconicAcid
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I haven't done a lot of chromatography, but I suspect that alumina is generally more acidic than silica. Maybe calcium carbonate would work?
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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Metacelsus
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I was thinking "basic alumina, Brockman grade I." For example: https://www.sigmaaldrich.com/catalog/product/sigald/199443 Note that it says the pH of a 5% suspension in water is 9.5
Judging by periodic trends, I would expect aluminum oxide to be less acidic than silicon oxide, all else equal. However, the acidity of alumina vs.
silica gel would probably depend on the method of preparation.
I haven't ever heard of calcium carbonate being used as a stationary phase, but I will look into it.
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byko3y
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Why haven't you already try to add triethylamine to the eluent? That's the first thing I think about, and you mentioned this option first too.
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