Melgar
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Dimethylethanolamine (DMAE) for Henry reaction?
In a different thread, it was recommended to use triethylamine as a catalyst for synthesizing the 1-phenyl 2-nitroalcohol that can be converted into
norephedrine. (or phenylpropanolamine/PPA. I'm trying to be nice to anyone in the future who's Uing the FSE  ) TEA is great for anyone with a fully-stocked lab, but unfortunately it seems to be hard to get for the average
person. Since it seems that many different amines make good catalysts, I noticed that DMAE (dimethyl amino ethanol, or dimethylethanolamine) has a
somewhat similar structure and is available as a nutritional supplement from vitamin stores everywhere. Presumably it's in the hydrochloride form,
but adding a strong base should cause it to separate out. Since only a catalytic amount is needed, this seems like a nice easy source of it. As for
the benzaldehyde and the nitroethane, well, that'll be for another day.
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Chordate
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The henry reaction usually takes place in anhydrous conditions. I think that otherwise you get a nitro-alcohol, or in this case instead of an alcohol
you might get a nitro-ether. In your example it'd still be a benzylic ether, so it'd likely come off just as easily as the alcohol, but this might
limit it's usefulness.
Why wouldn't you use ammonium acetate?
Edit: oh, my bad. I checked that mechanism and realized that the hydroxy group is formed of the ketone, and the presence of the acidic proton promotes
the elimination and formation of double bond. pKa seems to be inbetween TEA and pyridine. It might work, and getting it to form the alcohol or the
aklene might just be matter of careful control of concentration and reaction conditions.
[Edited on 7-3-2011 by Chordate]
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Melgar
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Well, I do actually want the nitroalcohol; no P2P for me, thank you very much. And I haven't actually heard of ammonium acetate being used in this
reaction. I do know the catalyst has a strong effect on yield though, so i want to choose a good one.
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Chordate
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It would actually form a styrene and not a ketone.
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Nicodem
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Try and see if it works.
Anhydrous conditions are not necessary. You can even use water as the solvent provided the aldehyde is soluble.
| Quote: | | Why wouldn't you use ammonium acetate? |
Because ammonium acetate does not work for the Henry reaction. It catalyses the Knoevenagel condensation instead. Bases like tertiary amines, KF,
K3PO4, hydroxides or carbonates are generally used for the Henry reaction, depending on the substrates.
PS: Melgar, please open referenceless threads only in the Beginners section where I'm moving this.
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Nicodem
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Thread Moved
8-3-2011 at 09:32 |
Chordate
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Ooh, i done got caught mixing up my condensations. I will go sit in the shame corner.
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