Sciencemadness Discussion Board

Reductions via Al/Ga alloys

VitaminX - 29-11-2012 at 06:55

Hi there guys.

I'm interested in the reactivity of Al/Ga alloys. I have read that they are similiar to aluminium amalgam but since I have no way to get me some mercury-salts and I don't want to have to deal with these toxic compounds I thought that might be a cool way around it.

But here is what I don't get. When you make amalgamated aluminium you can simply add the Hg(II)-salt in solution to your aluminium. Gallium however is not soluble in water, so how to make this alloy?
Then I thought: Just melt the gallium (30 °C) and drop it on the aluminium, but when I looked at the phase-diagram of Al/Ga this means that I need a lot of gallium to keep this in liquid state, which I don't want to do since then the reaction rate would be far too fast.

If I just melted 95% aluminium and 5% gallium together into a big lump then the surface area would be very little --> very slow reaction rate. Maybe I can create a big lump of alloy and then cut it into more pieces but I think it would be fairly hard.

Anyone got any ideas on how to accomplish that?
Also: I have found a lot on the internet on the ability of this alloy to produce hydrogen out of water, if I do my reaction in Ethanol (96%) will it react primarily with my reagent or with the water in the Ethanol. I know that it needs a little bit of water in order to reduce but still, which reaction is more favored?

Thanks

Nicodem - 29-11-2012 at 09:23

The aluminium surface can also be activated with tetrachlorocuprate anions. However, just like there are no literature examples for gallium based activations of aluminium, so there are none of this kind. But some amateurs confirmed tetrachlorocuprate works for the reduction of some substrates and published it on the Hyperlab forum. There has also been some discussion on this method, as well as the galium based activation, here on this forum, so UTFSE.

PS: Open threads without references only in the Beginnings section. Read the forum guidelines for more info.

VitaminX - 30-11-2012 at 08:51

Thanks for the reply, and sorry that I posted in the wrong section.

In that case I will try my best to make this reaction work, I will definitely look into it and post my results here.

VitaminX - 28-12-2012 at 06:34

Finally tried it, these are my results:

about 0.2g of elemental Gallium were spread out as a liquid on a crystallizing dish and little balls of Aluminium foil were rubbed against it until the Aluminium started to crumble. The small Al/Ga pieces were put in a beaker which was filled with MeOH and about 5 wt% Nitromethane. A little distilled water was added. Bubbling began and lasted about an hour, the Aluminium pieces turned dark-grey/black. The solution had an Nitromethane odor. We thought we could determine whether Methylamine was formed by heating the solution to reflux, but no smell of methylamine was present. 30% NaOH solution was added and the solution started vigorously bubbling (light grey). The solution became hot and green (quite strange).

Now the really interesting part begins: A smell very much like ammonia, but a little different became apparent. I don't know how methylamine smells but I read it has to be like ammonia and like fish. I am not sure about that as it didn't remind me very much of fish and I have been working with Triethylamine and Trimethylamine and certainly know how powerful thos amines smell so I kind of expected a similiar smell here but I only got this very less stinging ammonia-like smell. Anyone knows if that is what I am going for or is there an impurity in one of my reagents and NH3 was formed?

Thanks

smaerd - 28-12-2012 at 08:24

a test for basic volatiles such as amines is putting moist litmus paper over a flask or beaker etc. That might give you an extra step before doing actual analysis.

wireshark - 6-2-2013 at 15:42

I've just read up a little on Ga after reading this thread. As I understand it, you can easily recycle gallium from its alloys? So I can have fun with it over and over without buying more. New favorite element.

Okay, finding information on this has been a pain. I'm just bad at researching and finding relevant papers. Al + Ga = Al amalgam; Al amalgam + 3 H2O = AlO3 + Ga + 6 H2; Is this correct? If so, using pure aluminum and pure water, one could reuse the same precious Ga forever?

[Edited on 7-2-2013 by wireshark]

Organikum - 7-2-2013 at 11:48

Looks like Galinstan, the Aluminium/Gallium alloy can replace mercury also as liquid electrode in electrolytic setups.

This might bring back some of the better electrolytic synthesises......

/ORG

Dissertation attached is in german



Attachment: DissChannaa.pdf (1.5MB)
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Scr0t - 9-2-2013 at 01:03

Quote: Originally posted by VitaminX  
We thought we could determine whether Methylamine was formed by heating the solution to reflux, but no smell of methylamine was present. 30% NaOH solution was added and the solution started vigorously bubbling (light grey). The solution became hot and green (quite strange).

Now the really interesting part begins: A smell very much like ammonia, but a little different became apparent.

I have noticed when recovering MeOH from its azeotrope with MeNO2 which involved treating it with aq. NaOH followed by filtration & distillation also produces a strong amine smell during distillation (basic to damp litmus).
So the Al/Ga reduction may not be responsible for the presence of an amine in your case. I don't know what the reaction is though that makes the smell or the identity of the amine.

Organikum - 9-2-2013 at 05:44

Quote: Originally posted by wireshark  
I've just read up a little on Ga after reading this thread. As I understand it, you can easily recycle gallium from its alloys? So I can have fun with it over and over without buying more. New favorite element.

Okay, finding information on this has been a pain. I'm just bad at researching and finding relevant papers. Al + Ga = Al amalgam; Al amalgam + 3 H2O = AlO3 + Ga + 6 H2; Is this correct? If so, using pure aluminum and pure water, one could reuse the same precious Ga forever?

[Edited on 7-2-2013 by wireshark]


Yes. besides unavoidable mechanical losses of course and it will require to form a water soluble salt from the AlO3 in a way the Gallium is unaffected for good separation/extraction. What should be not so hard methinks. But isn't actually aluminium hydroxide formed first creating this ugly sludge?
Should be the best way to clean hydrogen nevertheless, just through a long tube with molecular sieves A3 and into the hydrogenation you go.... :D

Gallium as a replacement for mercury in reductions or reductive aminations works well, there is no need the whole surface of the Al being dulled if it is freckled thats fine and ready for use. Probably because the Gallium goes deeper into the Al. But for what reason ever, it works and thats the main point, being able to replace something poisonous with something at least much less dangerous without serious loss of yields.
It may not be in the literature but its in my private communications and for knowing where it came from makes it as trustworthy as any article (Org. Synth. might be an exception).

wireshark - 9-2-2013 at 20:17

Thanks, Organikum. Very encouraging to hear that Al-Ga alloys have been used for reduction (in the organic sense of hydrogen donation more than the electrochemical sense). I can't find any cases of it being used in literature. Plenty of Al-Hg reductions, though. The basic mechanism of aluminum activation is identical by Hg or Ga (see attached paper). The mercury doesn't have anything to do with the reducing power of aluminum once the pernicious oxide layer is depassivated. Ditto for Ga, so one can deduce that anything Al-Hg can do, Al-Ga can also do. Ga may be a more potent activator than Hg (no source for this statement), so perhaps there's a ratio like #.## mol of Ga is as good as #.## mol of Hg.

This would be a lot easier catalytic hydrogenation, safer to handle than mercury amalgams, and cheaper than both because Ga can be reused. I don't see any reason why Ga couldn't be reused after organic reductions, am I right? Maybe fractional freezing could work because it freezes a lot higher than any organic. To lose the Ga, it would have to reduce something else in solution, and based on the E° (Ga(III) + 3 e⁻ ⇌ Ga(s)) of -0.53, I don't see that happening.

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Mush - 1-5-2015 at 11:44

Inorganic Materials
March 2012, Volume 48, Issue 3, pp 238-243

Activation of metallic aluminum by tin and gallium chlorides in oxidation with water

A. G. Burlakova, S. P. Shilkin, O. V. Kravchenko, N. N. Dremova, S. E. Kravchenko, A. V. Ivanov, B. M. Bulychev

Attachment: Activation of metallic aluminum by tin and gallium chlorides in oxidation with water.pdf (940kB)
This file has been downloaded 689 times