Aluminum mercury alloy is used as a chemical reagent to reduce compounds, such as the reduction of imines to amines,in this case mercury destroy aluminium oxide layer which protect aluminium to react with water.

Alloy of aluminium and gallium which similar to above alloy make the aluminium more reactive by preventing it from forming an oxide layer.

In both cases mercury and gallium plays a same role of destroying oxide layer on aluminium to react with water but why can't gallium aluminium alloy reduce imines to amines like mercury aluminium alloy ?

  • $\begingroup$ Lol, exactly the same question was ask by me on a chemistry forum and never received any replies. I believe you can interchange them in some circumstances, but I don't know the details. This would be especially useful because gallium is a lot less dangerous to the amateur (and perhaps to the professional as well, or at least less toxic waste) chemist. Also gallium is pretty cool as it melts in your hands and solidifies again when restored at room temperature (i.e. removed from your hands). $\endgroup$ – Jori Jun 1 '14 at 18:04
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    $\begingroup$ Oh almost forgot. For the person who answers this question, I'd recommend to be careful (we all like to learn, but there are always shady figures abusing chemistry) as Al/Hg reduction is a very popular method for producing crystal meth and MDMA (for P2P and MDP2P respectively). Seeing that this is the users first question on any SE network site, it could be the case that the questioner seeks a safer alternative to this reduction. Providing this information to someone with the intent to manufacture illegal substances could be illegal depending on where you are from. $\endgroup$ – Jori Jun 1 '14 at 18:06
  • $\begingroup$ Also read sciencemadness.org/talk/viewthread.php?tid=14173 and probably (if you didn't) en.wikipedia.org/wiki/Aluminium_amalgam. $\endgroup$ – Jori Jun 1 '14 at 18:22

We can rationalize the differences in the reactivity as follows. Gallium has a higher ionization energy compared to mercury. During a redox reaction the metal is oxidized and it loses an electron, therefore how "easy" it is for a metal to lose its electon is iimportant. Since gallium is harder to inonze than mercurey, it implies that it is "easier" for mercury to lose its electron compared to Gallium, making mercury a better stronger reducing agent.

I may come back and add some quantitative information later, but i'm going to go eat now. I think looking in a table of standard reduction potentials would be reasonable.

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    $\begingroup$ Mercury loses an electron? It gets an electron from $Al(s)$. I'm not quite sure if I can follow your answer. Perhaps you should elaborate on the exact workings of amalgamation. $\endgroup$ – Jori Jun 1 '14 at 23:13

I cannot think of any reason that it can't. Mercury and gallium should both be acceptable mediators for the electron transfer. In fact, elemental Gallium may even be preferred over salts of Gallium unlike Mercury, where only Mercuric salts can be used (maybe due to mercury having such a low melting point?). Elemental Gallium might actually have an added advantage of having the perfect melting point to mediate electron transfer.

It would actually be quite ironic if all these chemists are taking elemental mercury and making salts of it just to give it the properties of elemental Gallium!

And I'm not even touching on the toxicological superiority of gallium!

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    $\begingroup$ This seems very speculative. Do you have any references to support your claims? $\endgroup$ – bon Sep 5 '15 at 15:14

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