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Author: Subject: A small experiment with Al/Ga alloy - reduction of nitromethane
Dagda_Mor
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[*] posted on 19-6-2016 at 08:59
A small experiment with Al/Ga alloy - reduction of nitromethane


Today I have decided to test the reduction potential of Al/Ga alloy.

After several unsuccessful attempts I have come to the conclusion, that if I preheat the gallium in oven in a crucible at around 200C the Al-foil is easily dissolved in the gallium. At normal temperature the dissolution is much slower - several days are needed.

The gallium stains easily everything it touches. Despite my efforts I could not successfully clean the crucible which I used for heating the gallium.

Now to the interesting part of the story:

1) I had some Nitromethane lying around, so I decided to test whether the alloy will reduce it to methylamine. Unfortunately after I added two drops of nitromethane:ethanol 50:50 mixture, neither gas evolution nor fishy smell were noticed.

The gallum is 99.9 pure, the nitromethane however is fuel grade of unknown concentration and very unpleasant smell. It burned with a specific pale yellow flame and when burning it evolves a NO2-like smell.

2) After I added around 50ml of tap water to the alloy as expected a vigorous gas evolution was noticed, The reaction looks like I have put a effervescent vitamine tablet in a glass of water, but with the difference that the mixture quickly turned into a black nasty suspension because of the aluminum (hydro)oxides.

I also noticed that the gallium is much more easily handled underwater, so after several decantions of the suspension it was successfully recoved.

After the experiment one question remains open :

Why no gas evolution/smell were noticed when I added 2 drops of nitromethane dissolved in ethanol to the potent Al/Ga alloy ?

Thanks in advance for your time reading this thread and for your opinions !
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laserlisa
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[*] posted on 19-6-2016 at 09:04


Are you not supposed to add some acid to get H2 evolution?

[Edited on 19-6-2016 by laserlisa]
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Crowfjord
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[*] posted on 19-6-2016 at 09:08


You added the nitromethane straight to the plain alloy? A solvent is usually employed, like an alcohol. The metal transfers electrons to the substrate, but a proton source is still needed for the full reduction to amine. Also, acid is usually added to prevent dimerization. See this thread for more on Al/Ga reduction. There are more on the forum as well.

[Edited on 19-6-2016 by Crowfjord]
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Dagda_Mor
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[*] posted on 19-6-2016 at 09:12


Quote: Originally posted by laserlisa  
Are you not supposed to add some acid to get H2 evolution?

[Edited on 19-6-2016 by laserlisa]



Al is powerful enough reductor to replace hydrogen in the water molecule, thus evolving hydrogen and making an emulsion of hydroxides. However under normal curcumstances, oxide layer prevents Al to show its reduction potential. Thus Ga or Hg is needed to break this oxide layer. Ga is not toxic and cumulative poison so I prefer Ga over Hg despite its high price.

No acid is needed IMO in both cases. It was expected, that nitromethane will be reduced to gaseous methyamine -> gas evolution and fishy smell, but unfortunately nothing of this really happened.
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Dagda_Mor
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[*] posted on 19-6-2016 at 09:23


Quote: Originally posted by Crowfjord  
You added the nitromethane straight to the plain alloy? A solvent is usually employed, like an alcohol. The metal transfers electrons to the substrate, but a proton source is still needed for the full reduction to amine. Also, acid is usually added to prevent dimerization. See this thread for more on Al/Ga reduction. There are more on the forum as well.

[Edited on 19-6-2016 by Crowfjord]


The nitromethane was dissolved in 70% ethanol. Won't the protons be delivered from the reduced by the Al water in the mixture and used to fully reduce the imine to amine?

When reading the Rhodium archives : https://erowid.org/archive/rhodium/clandestine/gonzo/index.h...

"A Photo Essay on the Nitromethane Al/Hg" - no acid is used for the reductive amination. Why in this case an acid like HCl is needed as proton source ?
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[*] posted on 19-6-2016 at 09:39


Sorry, I missed that in the first read. Since you used alcohol, it seems like something should have happened. I made a little mistake: acid is used with reduction of nitroalkenes, to prevent dimerization and polymerization by Michael reaction. Since you used a nitroalkane, this shouldn't be a problem. Acid is also not absolutely necessary in reductive aminations of aldehydes or ketones. The water and alcohol of the solvent serve as proton sources.

The purity of nitromethane probably played a role. The other crap in there may have interfered with the reaction. Also, according to the thread I linked, apparently very pure gallium doesn't seem to work as well for some reason.

[Edited on 19-6-2016 by Crowfjord]
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Melgar
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[*] posted on 22-6-2016 at 11:25


I've done a similar reaction plenty of times, although I always used galinstan, an alloy of gallium, indium, and tin, with a melting point below room temperature. I typically melted pure aluminum (usually from Al wire) into a globular shape with a torch, then mixed in the several drops of galinstan I got from the thermometer. The galinstan makes the aluminum easy to break up into chunks, which oxidize noticeably in the presence of air, so I kept them stored in a jar. A chunk added to methanol and nitromethane would evolve an ammonia-like fishy smell, which I assume was methylamine gas. This would even work with Top Fuel, which is a mixture of 20% nitromethane ~70% or so methanol, and ~10% or so lubricants.

The would also work in isopropanol (I think), but then you have to worry about potential reactions from aluminum isopropoxide, if there are any ketone or aldehyde groups present. For some strange reason, a large number of people on this site seem to want to use aluminum and gallium for reductive amination of ketones. But if that reaction were performed in isopropanol, the aluminum isopropoxide might just transform all those painstakingly prepared ketones into their corresponding alcohols, while producing acetone as a byproduct.

Edit: your grey sludge end-product can be dissolved by dilute hydrochloric acid. If your reaction vessel is above gallium's melting point, you should see your gallium precipitate as little metal droplets at the bottom.

[Edited on 6/22/16 by Melgar]
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