Al catalyst questions...

[Tengo]

I've used the TFSE (trust me), but couldn't find answers to a couple of questions.

As I understand, in the Al(Hg)-nitro reduction one should use Hg to treat the surface of Al because of the Al2O3...
But what if someone can order Al flakes that are "surface treated". Could the Hg be omitted?

And another question... Could the amalgamation be done with Al powder (<0.08 mm) and liquid Hg. And then be used in the reaction? Or does it have be the squares, flakes etc?

[Diggity]

Could the amalgamation be done with Al powde.

I think everyone has asked that questions once or 137 times, NO. it would react way to fast.

But what if someone can order Al flakes that are "surface treated".

I don't know what that means "surface treated" Mayybbbee, it's surface treated with al203!!
& I'm, somethin of a phenom, no need for da cron, I'm un-stopable.   
 

[Barium]

Amalgamated aluminum powder would be troublesome to handle and give violent exoterms. Amalgamation is done to remove the oxide layer from the surface. There is no way the oxide layer could be removed and the surface stay "clean". It would be oxidized in seconds again. How has the aluminum surface been treated in the product you mentioned?

also, the aluminum is not a catalyst it is a reducing agent.

Catalytic hydrogenation freak

[Tengo]

I'm not sure, but:
One would assume that if it's not "surface treated", there would be Al2O3 on the surface.

[Diggity]

Al 203, if I read correctly, is a protective layer. Is something is "treated" it could mean it's being "protected"

Ie, you coat your back patio deck with anti rot shit = protective layer.. I dunno either, just sounded odd and I've gone down this road too, and had little luck.
& I'm, somethin of a phenom, no need for da cron, I'm un-stopable.   
 

[moo]

You see, when the aluminum reduces anything (be it air or whatever you wish to reduce) it gets oxidised. That's how the layer of Al₂O₃ forms. So theoretically, with this surface treated aluminum you could do some (which doesn't mean it would be an amount of any use at all) reductions before you would have another layer of Al₂O₃. In other words: you surface treat it with Hg and you get rid of the problem.

[Anansi]

The mercury does serve to strip the Al of its protective Al₂O₃ layer to allow reaction to occur at a usable rate.

The aluminium would first just reduce any water in the system, forming hydrogen gas and sludge, but the mercury layer changes the electronic properties of the aluminium surface. Read up on "hydrogen overvoltage" for an explanation of how/why this works. This effect provided by the mercury is also necessary for the Al to reduce anything useful for us.

So I'd say the 'surface treated' alunminium flakes wouldn't suffice in this situation. Unless the surface treatment was mercury of course  

Hope this helps,

...Anansi

[Aurelius]

Do you have a specific link for information on the hydrogen overvoltage or did you just mean to a search in general?

[Chromic]

Anansi, what you said, isn't quite correct. There are many examples of dissolving metal reductions. Few of them require mercury. (eg iron, zinc & sodium) There are also many examples of Al being used to reduce without mercury as well. I'm sure it will reduce nitromethane (some people have done it here) and there's examples of it reducing nitrotoluene as in the quinones document. (ie "alkylnitrobenzenes are reduced with powdered Aluminum and aqueous acid")

However, you do require to remove the passive surface coating... also sometimes the acidic or basic rxn conditions aren't going to jive with your reactants... sometimes you can also use transition metal catalysts with the aluminum to enhance the reactivity of the reduction (eg using nickel and aluminum to reduce phenylnitropropenes)..

So for the record, I'm not saying that people should stop using mercury in their reductions, just that not all reductions using aluminum require mercury.

[lab_bitch]

To the best of my knowledge, the mercury substitutes into the crystalline structure of the external surface of the aluminum, forming an alloy.  I may be incorrect, but I believe that this alloy has a higher reduction potential than aluminum, making it less reactive.  Mercury is used for the same purpose when sodium is used as the reducing metal.  Without the decrease in reactivity provided by the mercury, the aluminum would readily react with the solvent to form hydrogen gas at certain pH levels.  Other than that, I don't really know much about the role of the mercury.  Does the mercury remove the initial layer of Al2O3 or does the decrease in pH produced by the mercury salt remove it?  Does the surface of the aluminum become saturated with mercury at a certain surface concentration?  If so, is this saturation usually reached while amalgamating?  Is it better to have more or less mercury concentration on the surface?  Does a higher surface concentration of mercury decrease the reaction rate of the aluminum with the solvent? the nitromethane and ketone?  Do the electrons donated to the nitro/ketone come from the aluminum atoms or the mercury atoms?  Does this electron transfer proceed by a free radical mechanism, or do the reactant coordinate to the metal surface?  I'm sure that most of these questions cannot be answered here, but I have been trying to research the mechanism of this reaction in the library and have found nothing written in English.  I did find an article on the reaction mechanism in either French or German.  Can anybody translate this?

[Rhodium]

There are good enough translating bots online.

[lab_bitch]

Are there any that can translate chemistry language?

[Rhodium]

Not exactly, but the german chem words at least so similar to english that you'll understand.