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Author: Subject: Gallium salts for amalgamation of aluminium?

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[*] posted on 21-3-2010 at 02:51
Gallium salts for amalgamation of aluminium?

I want to do a reduction of nitromethane to get my hands on some methylamine and saw one method on the net involving an Al/Hg amalgam. While I don't currently have any mercury, and would rather not deal with it if possible, I do have a small sample of gallium and was considering making a little of the chloride as a substitute. What are peoples' thoughts?

[Edited on 21-3-2010 by 12332123]
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[*] posted on 21-3-2010 at 08:17

This would be an expencive substitution but i dont think it would work as gallium does not form alloys with aluminium as rapidly and mercury does.
It might be worth experimenting with however...
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[*] posted on 21-3-2010 at 18:20

Ah interesting, I have been wondering the same thing for a while, but since I dont have a need to use any amalgams I have not really looked into it. Though I really encourage you or anyone else to look into it, it would be awesome to find a substitute for mercury even if it is many times more expensive. Because mercury is just so darn toxic and cumulative. I am inclined to think that it would work, mainly because I have seen a number of aluminum gallium alloys evolve hydrogen on contact with water. So as you continue on keep us posted!

P.S- There are easyer ways to make methlyamine, formaldehyde + NH4Cl= methlyamine HCl. Check this thread out
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[*] posted on 21-3-2010 at 19:35

can't the nitro group be reduced by Na/alcohol? It seems like I read that somewhere. Why not buy the MeAm? I have little jars of the stuff in my lab that I made through the tedious formaldehyde process and a nice bottle of 40% in the refrigerator I bought.

[Edited on 22-3-2010 by chemrox]

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[*] posted on 21-3-2010 at 20:39

One possible problem is, will gallium be reduced to metal in aqueous solution? Will the local environment at the aluminum surface reduce it despite that? (That's potentially like making sodium amalgam in mercury -- you can reduce it to metallic form despite the aqueous interface.)

I wonder if other metals might work -- hard to find a metallic liquid other than gallium and mercury, but indium is soft and low-melting; maybe it would disrupt the surface oxide, or diffuse into the metal and do something.

And of course, tetrachlorocuprate ions eat aluminum with a vengance, but I seem to recall that was evaluated on this forum before and found to be ineffective (consumed rather than catalytic?).


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[*] posted on 22-3-2010 at 05:40

Also bear in mind the simple Zn or Sn/HCl reduction of nitro groups, which is right up there for ease of reaction and also obtention of reagents.
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[*] posted on 22-3-2010 at 07:08

Gallium metal wets almost everything. You might not even need to make salts. YT2095 had been talking about a hydrogen generator at some point that used gallium metal and beer cans. I'm under the impression that he had it running.

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[*] posted on 23-3-2010 at 07:57

To my knowledge aluminum treated with gallium will happily reduce water to hydrogen the way aluminum amalgam does. But if you want to reduce a nitroalkane you have to consider hydrogen overpotential of the gallium-aluminium compared to aluminium amalgam. That is what dictates the selectivity (substrate reduction vs. hydrogen evolution). This is the same idea as in electrolytic reductions where you have to use electrodes made of suitable materials (mercury and lead are traditional choices) to be able to actually reduce your compound instead of making hydrogen gas.
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