Author Topic: methanolic MeAm via Al/Hg  (Read 2514 times)

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spric

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methanolic MeAm via Al/Hg
« on: December 10, 2001, 12:41:00 AM »
No answers from TFSE satisfied, so here it goes.
Are there possibilities of making a methanolic solution of MeAm via the Al/Hg from MeNO2?  Finding the amount of MeAm in solution would be easy, as is drying to remove that water.   Even at low temps, would vacuum filtration of the sludge solution boil off all of the fishy goodness?  Obviously even after careful filtration you will have some Hg, MeNO2, and Al present.  NaBH4 doesn't do shit to MeNO2(or does it?) and dave has seen NaBH4 reactions in text where Hg was a present end(waste) product.  Now what about any Al present?  Also, could a flask full of Al be loaded all to hell with a shitload of MeNO2 being that those small nitro compounds reduce so damn easily?  So basically, is it possible to get a methanolic solution from nitromethane and Al/Hg that is a high enough concentration and clean enough to perform a borohydride reductive amination on?

4:20

Chromic

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Re: methanolic MeAm via Al/Hg
« Reply #1 on: December 10, 2001, 04:32:00 AM »
Just a suggestion, but why not try to distill out the MeAm in MeOH?

psychokitty

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Re: methanolic MeAm via Al/Hg
« Reply #2 on: December 10, 2001, 04:19:00 PM »
From what I've heard, the problem with MeNH2 synthesis using this route is with the concentration of methylamine in methanol you would get after the completion of the reaction. 

Al/Hg reactions occur at reflux temp, and when you calculate just how much nitromethane will be converted into methylamine, you can see that the ratio of it to solvent is in the order of about 2%.  This probably is so because at reflux temp, any higher concentration of methylamine in methanol solution will be driven off from the mixture.  So no matter what, unless this reaction occurs at low temps, you will end up with considerably less than 5% methylamine in methanol.  I suppose if you stirred the mixture at low temp, the reduction might still occur with concommitant conversion of Al/Hg into aluminum hydroxide.  But this is only theoretical as I have never tried this reaction.

Sounds like a no-win, but hey, anything's possible.

Osmium

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Re: methanolic MeAm via Al/Hg
« Reply #3 on: December 10, 2001, 04:20:00 PM »
> Are there possibilities of making a methanolic solution
> of MeAm via the Al/Hg from MeNO2? 

Yes. I often reused the MeNH2-loaded, rotovapped EtOH from Al/Hg reactions. But it won't be anhydrous.

> Even at low temps, would vacuum filtration of the sludge
> solution boil off all of the fishy goodness?

No. But it surely can't hurt to bubble the exhaust gasses of your (hopefully clean!) full teflon diaphragm pump through some water, and also make sure that the alcohol is cold when you filter it.

> Obviously even after careful filtration you will have
> some Hg, MeNO2, and Al present. 

Hg: no. MeNO2: maybe a little bit. Al: not when there is enough H2O around.

> NaBH4 doesn't do shit to MeNO2(or does it?)

NaBH4 is basic enough to convert the MeNO2 into the Na salt, so you will probably produce 1mol H2/every mole of MeNO2 present. No big deal, just use a little bit more of NaBH4.

> Now what about any Al present?

Shouldn't matter at all if there still was any.

> Also, could a flask full of Al be loaded all to hell with
> a shitload of MeNO2 being that those small nitro
> compounds reduce so damn easily?

The reaction is way too exothermic to add MeNO2 directly to Al/Hg covered with a little H2O/EtOH. You might succeed by slowly dripping the MeNO2 into the pre-warmed mixture, but the generated gas will be far from anhydrous.

> So basically, is it possible to get a methanolic solution
> from nitromethane and Al/Hg that is a high enough
> concentration and clean enough to perform a borohydride
> reductive amination on?

I doubt it, not with some serious tweaking. I'd rather neutralise the filtered alcoholic solution with HCl, remove the alcohol by distillation, and use the isolated methylamine hydrochloride to generate MeNH2 gas