Melgar
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Aluminum alkoxide-amine adducts
Or AAAA for short. Anyway, I've been using an aluminum alloy to reduce nitro groups to amines with an alcohol solvent, and have noticed that when the
reaction is finished, my TLC plate seems to indicate that there's not much at all in the sample I put on it. Of course, at that point, my solution
would be anhydrous, and provided these AAAAs are present, the amines would all be in the sludge at the bottom, and not part of my sample. Simple
hydrolysis should liberate them, I'd imagine, but then the aluminum forms a goopy sludge that's impossible to filter.
Two ideas come to mind:
First, add a moderately strong acid. Preferably an alcohol-soluble organic acid, say GAA, formic acid, or oxalic acid, which would react with the
adduct, releasing the amine as a soluble salt. (I hope) I guess the next step would be to add a lot of alkali hydroxide to dissolve the aluminum, and
release the amine to an organic layer. I'm not 100% sure that'd work
Second, dissolve the whole mess at the bottom in alkali hydroxide and water, then titrate the solution with phosphoric acid. Aluminum phosphate has a
very low solubility in everything, and phosphate salts are easy to separate. Of course, that assumes that the salts will be easy to separate, though
I have no reason to believe they wouldn't be. AFAIK, only sodium, potassium, and ammonium/amine phosphate salts are water-soluble, and potentially
some amine phosphate salts may even be alcohol soluble?
It's been hard finding much information on these adducts, but they definitely seem to be a phenomenon. Here's one article that mentions them:
https://books.google.com/books?id=kkg3xJ4sifgC&pg=PA4&am...
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clearly_not_atara
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If the "sludge" dissolves in alkali, couldn't you extract the resulting solution directly with e.g. DCM?
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Melgar
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The aluminum is not super pure, and various metals and their oxides are present that end up precipitating out. Virtually everything dissolves in, say,
HCl though. But the main reason I didn't want to do that is that right now, I just want a proper TLC test of the reaction to see what the products
were like; I don't want to do the workup just yet.
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DraconicAcid
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Then you may want to take a small sample, make it really basic, extract that with dichloromethane, and run a TLC of the extract.
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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JJay
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How does TLC indicate the amount of your product?
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Alice
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Mini-workup is the standard procedure for TLCing TLC incompatible mixtures. If you can't separate the sludge from the solvent, open up a syringe,
press some cotton onto the bottom so it's really tight. Then add the solution carefully and close the syringe. Press the solution through the syringe.
If the compounds you're trying to find are highly diluted (or bound to the alkoxide almost but not completely) you may dot it 20 times or more on the
same spot. This also helps to find minor components. Depending on the eluent the amine won't move and therefor won't move away from other sticky
compounds so you won't be able to distingish it from other compounds.
If the amine sticks to the alkoxide which I think may be possible, and you don't want to do any workup, then you have a low chance doing a successful
TLC.
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