Sciencemadness Discussion Board

Reduction Al-Hg

Filemon - 30-9-2007 at 14:55

I don't know exactly beacuse I have failed in an amalgam reduction of Al-Hg/AcOH. I believe that it is because the sheets of Al were too fine then too much Hg has absorbed (Al reacted too strong with the salt of Hg). What has caused that the attack of the AcOH is too slow. Which the failure has been exactly?

Sauron - 30-9-2007 at 20:40

You want to reduce AcOH?

The active reducing agent in an Al amalgam reduction is the aluminum alkoxide, if you use anhydrous ethanol it is Al(OEt)3 that will do the work.

Make your amalgam, then dissolve it in dry ethanol under reflux. You can calculate how much Al ethoxide you made from the mass of Al you added.

Then add only the amount of your substrate to be reduced, equivalent to the alkoxide present.

Just dumping Al foil (with or without painting with HgCl2) will just get you a dissolving metal reaction, in absence of alcohol, if you are putting it in excess AcOH. You might reduce a little AcOH that way. But mostly that's just making aluminum acetate contaminated with mercury acetate.

[Edited on 1-10-2007 by Sauron]

Filemon - 1-10-2007 at 08:24

I have forgotten to say the substratum that I want to reduce. I want to reduce nitromethane to make methylamine.

Sauron - 1-10-2007 at 10:02

Surely there's an embarassment of choices of reducing agents for that one?

Furch - 1-10-2007 at 10:11

Sauron, what reducing agent would you choose to reduce nitromethane to methylamine? I think Al is an excellent and cheap choice... Either that or Fe or Sn.


- Furch

Sauron - 1-10-2007 at 10:42

I was going to suggest Fe or Sn either one with HCl, classic dissolving metal reduction.

I think filemon's procedure was a mistake. He was reting to use Al amalgam when plain Al foil would have done fine. For the amalgam he should have been using an alcohol as reaction medium, the HgCl2 is just to clean off surface oxidation to let the alcohol get at the Al. But instead he was using AcOH which would eat right through the oxide anyway. So I thin he was confused.

Anyway, something went wrong and the rxn failed. Did he get proprtions right? I don't know as he has not been very specific.

My advice would be to look up a proven procedure from the literature (neither Wiki pls) and follow the procedure.

I would think Fe filings, Sn and muriatic acid would all qualify as otc. I won't ask where the MeNO2 came from and pls don't tell me what the MeNH2 is for. I don't want to know.

Furch - 1-10-2007 at 11:20

I agree with Sauron!

Also, Sauron, don't worry... He's probably just going to make some benign chemical warfare agent, not any kind of horrible drug ;)

Sorry man, couldn't resist ;)

Peace out.

bio2 - 1-10-2007 at 14:09

....."He was reting to use Al amalgam when plain Al foil would have done fine".........

Are you trying to say that Al with HCl will reduce MeNO2
same as Fe or Sn?

Al amalgam in alcohol will reduce nitromethane to methylamine.

I thought that the reaction occurs at the surface of the Al amalgam
transferring electrons rather than a reaction with the alkoxide. This is more akin to a hydrogenation rather than a reduction in the normal sense.

[Edited on by bio2]

Sauron - 1-10-2007 at 21:42

He was using neither HCl not EtOH. He was using AcOH, go read his post.

And he gpt no reduction.

I am suggesting that if he wants to reduce MeNO2 he should go find an example of that reduction by his chosen reducing agent if he can and follow it, rather than trying to improvise.

Sauron - 1-10-2007 at 21:46

I don't care if some one wants to make MeNH2.

And I also don't care if someone wants to make a CW agent as they will probably die in the attempt, and rid the world of their shadow.

A self correcting problem!

Nicodem - 2-10-2007 at 04:14

Quote:
Originally posted by Sauron
The active reducing agent in an Al amalgam reduction is the aluminum alkoxide, if you use anhydrous ethanol it is Al(OEt)3 that will do the work.

Al(OEt)3 can not reduce anything as there is no such thing as chemical species of aluminium with the oxidation state above +3. Aluminium cations simply can not give any more electrons. It is the aluminium (0) that is the reducent. The reaction is analogous with electrochemical reductions at any cathode with an appropriately high hydrogen overvoltage (and as such it does not have to be anhydrous nor is it particularly sensitive to the proton donor – acetic acid work just as fine and so does water or ethanol). Contrary to what bio2 says it has no relation whatsoever with catalytic hydrogenations. The mechanism is totally different.

Sauron - 2-10-2007 at 06:18

True but a little less than germaine. The chap's reaction did not work, despite all of that. So why not? And wat does he do next?

My suggestion stands.

Nicodem - 2-10-2007 at 12:25

I could not care less for why Filemon failed in his nitromethane reduction. I did not reply to give advices or explanations to someone who is so lazy as to ask them without giving any useful information for a reply. I doubt he really expected any answer at all or else he is terribly naive. I only wanted to correct claims some might take for true and spread the misinformation further. It is important to correct errors at their origin or else, after several repetitions, they became common belief (I have seen this done too many times).

trilobite - 2-10-2007 at 13:23

Quote:
Al(OEt)3 can not reduce anything as there is no such thing as chemical species of aluminium with the oxidation state above +3.


Except in the Meerwein-Ponndorf-Verley -reduction, where it can be used, but surely that is not what people usually mean by Al/Hg.

Nicodem - 2-10-2007 at 13:35

In that case it is isopropanol that is the reducent, not the aluminium ions. The isopropoxide groups get oxidized to acetone while the ketone substrate gets reduced to the alcohol. The aluminium (or titanium) isopropoxide only works as a catalyst. That is however a very interesting reaction with a still somewhat obscure mechanism.

Sauron - 2-10-2007 at 16:46

@Nicodem, this thread has no raison d'etre at all, other than to assist filemon with his reduction of nitromethane to methylamine.

If your negativity is to prevail then this thread ought to have been consigned to DETRITUS at the onset.

A agree that filemon was rather parsimonious with details but at least I advised him to crack a book and find out how to do it right.

All you did was nitpick my post concerning the mechanism of a reaction that I have not conducted since the mid 1970s. Shame on me for not remembering correctly. Shame on you for being such a pedantic sort. The world will little note nor long remember this thread.

Sergei_Eisenstein - 3-10-2007 at 10:27

In the scientific community, correcting and being corrected is standard procedure. If you cannot deal with this "nitpicking", it is advisable to refrain from the discussion.

Filemon - 3-10-2007 at 14:44

Thank you for your help. I have tried to reduce 1.5gr of nitrometane with 7.5gr of Aluminum (I have activated it 50mg of HgCl2) and 50ml of AcOH + 15ml of H2O. I believed that it had not activated the aluminum well but it doesn't seem him for what you say. I have activated the aluminum with a breakup of 200ml and 50mgr of HgCl2. The reaction with the aluminum was quick and vigorous, leave it 9 minutes. I surprised this because the reaction should be neither so strong nor so rapid. Perhaps it has failed because the aluminum has some impurity that poisons the catalyst.

I will prove the Urushibara catalysts because it stops my the AcOH it is expensive. Can you use in the amalgam Al-Hg HCl instead of AcOH?

Sauron - 3-10-2007 at 18:19

@Sergei, what I object to is Nicodem's unwillingness to help the thread author.

@Filemon, why don'y you try EtOH instead of AcOH?

Also try Al in AcOH without the Hg treatment. I think you will find that the AcOH will dissolve your Al at the same rate, and that the EtOH will require reflux to do so.

I never had a failure with Al/Hg in EtOH, nor with LAH/TiCl3 in THF.

chemrox - 3-10-2007 at 22:34

I think this thread is getting interesting.. I've been hearing about Al/Hg amalgam as a reducing agent for reductive aminations on carbonyl groups all my chemistry life. The Al-isopropoxide reaction is new one to me and I'd like to understand it. So, everybody lighten up, there's some chemistry here worth discussing.

Filemon - 4-10-2007 at 08:54

Quote:
Originally posted by Sauron
@Sergei, what I object to is Nicodem's unwillingness to help the thread author.

@Filemon, why don'y you try EtOH instead of AcOH?

Also try Al in AcOH without the Hg treatment. I think you will find that the AcOH will dissolve your Al at the same rate, and that the EtOH will require reflux to do so.

I never had a failure with Al/Hg in EtOH, nor with LAH/TiCl3 in THF.


What functional groups can it reduce with Al-Hg/EtOH? What proportion of reagents?

[Edited on 4-10-2007 by Filemon]

chemrox - 4-10-2007 at 11:13

The way this thread starts there seems like a prior discussion was underway and the thread comes in the middle with Filemon answering a question with "I don't know.." Now @Nicodem: "It is important to correct errors at their origin or else, after several repetitions, they became common belief (I have seen this done too many times). " Aside from his characteristic impatience this is a most valid point. Please jump into any thread, one and all, to correct mis-statements.

I didn't see where the procedure used was really vetted. The Al should have been reacted with HgCl2 until a gray precipiate fromed and there were bright spots on the foil. Then the foil should have been washed, dried and used in IPA. Is the Al combined with Hg? I rather think so hence the shininess. It is mostly used in reductive aminations to reduce the imine formed in the reaction between the amine and carbonyl. This is my limited understanding and I'd like to know more. But to help filemon, go through a published use where the details are given or try to find the procedure in an older lab manual. See if you did it right.

[Edited on 4-10-2007 by chemrox]

Mush - 10-10-2014 at 12:53

I've been studying aluminium amalgam reductions (Al-Hg), so far I've bumped into some very interesting papers.

From EROS:
Aluminum (aluminium)
Aluminum Amalgam (aluminium amalgam)


THF–water Al(Hg) system
"2. Preparation of the nitrone 24a" experimental section
J. Chem. Soc., Perkin Trans. 1, 2000, 3487–3494

"26. Desulfonylation of sulfone 3c. Representative procedure
(method A). "
Tetrahedron Letters 46 (2005) 3311–3313

Attachment: Aluminum Amalgam EROS (Wiley).pdf (169kB)
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Attachment: Aluminum EROS (Wiley).pdf (259kB)
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Attachment: J. Chem. Soc (163kB)
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Attachment: TL 46 (2005) (112kB)
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[Edited on 11-10-2014 by Mush]

Mush - 10-10-2014 at 14:00

"Reductions with Aluminum
Reductions with aluminum are carried out almost exclusively with aluminum
amalgam. This is prepared by immersing strips of a thin aluminum foil in a
2% aqueous solution of mercuric chloride for 15-60 seconds, decanting the
solution, rinsing the strips with absolute ethanol, then with ether, and cutting
them with scissors into pieces of approximately 1 cm2 [141,142]. In aqueous
and non-polar solvents aluminum amalgam reduces cumulative double bonds
[143], ketones to pinacols [144], halogen compounds [145], nitro compounds
[146, 147], azo compounds [148], azides [149], oximes [150] and quinones
[151], and cleaves sulfones [141, 152, 153] and phenylhydrazones [154] (Pro-
(Procedure 30, p. 212).
Several reductions have been achieved by dissolving a nickel-aluminum
alloy containing usually 50% of aluminum in 20-50% aqueous sodium hy-
hydroxide in the presence of a reducible compound. Since under such conditions
elemental hydrogen is generated by dissolution of aluminum, and since Raney
nickel is formed in this process, such reductions have to be considered cata-
catalytic hydrogenations rather than dissolving metal reductions. Their outcome
certainly points to the former type. "

Reductions in Organic Chemistry - Hudlicky M.
Page 27

https://www.mediafire.com/?4eo9h4ibeotzqgq