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Author: Subject: aluminum electrolisis in ethylene diamine?
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[*] posted on 26-8-2004 at 13:04
aluminum electrolisis in ethylene diamine?


i once read that aluminum hydroxide was soluable in ethylamine, so i was wondering if aluminum hydroxide or aluminum oxide could be electrolised in ethylene diamine since aluminum metal is not normally attacked by amines.
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[*] posted on 26-8-2004 at 15:08


"Aluminium metal is not normally attacked by amines", but "aluminium hydroxide soluble in ethylamine". Aluminium and its oxide/hydroxide are amphoteric, meaning that it dissolves in sufficiently strong alkalis or alkaline solutions to form aluminates, AlO2- or AlO(OH)2- or Al(OH)6--- and other species including polynuclear depending on concentration and conditions, as well as Al salts (liable to extensive hydrolysis in water at high pH) with acids. However, the alkali or acid concentrations have to be high, for any significant reaction to occur, especially with solid Al2O3. To be soluble in ethylamine, it may be because Al(OH)3 forms an aluminate with it; at the very least, like Cu++, it would probably form a soluble amine coordination complex.

The usual method of production of Al metal, discovered in 1886, is by electrolysis, at quite a high voltage, of alumina, Al2O3, usually in fine powder form obtained by refining bauxite, dissolved in molten cryolite, Na3AlF6, which is either mined in Greenland or made artificially. Pure Al2O3 has much too high a melting-point to be used alone.

The reasons why aqueous or amine solutions of Al salts or Al oxide/hydroxide are not used appear to be partly the enormous liberation of energy that has to occur for reduction to the metal (which would evaporate the solution), and partly the extensive degree of hydrolysis of Al+++ that occurs in such solutions which greatly slows down its migration to the cathode. The same largely applies to the production of other electropositive metals, like the alkali metals, alkaline earth metals, and rare earth metals, which can be obtained only by electrolysis of molten halides. In the case of alkali and alkaline earth metals except Be, it is also because of their reactivity with H2O and amines to form hydroxides and amides. Slightly less electropositive metals like Zn are borderline cases - electrolytic galvanizing of iron can be done by electrolysis of aqueous solutions.

John W.
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[*] posted on 26-8-2004 at 17:12


Well, of course, ethylene diamine is a strong complexant. I suspect it works similarly to acetylacetone, where various metal ions are complexed (even things such as beryllium).
Anyway, xxxxx, do you have a reference to this? It might help to figure what is going on.
But you are asking for ethylamine, not diamine.
Makes this more difficult to understand, admittedly.
Still it's interesting to hear that this could be dissolved - but some qualified ref. please!




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[*] posted on 27-8-2004 at 09:37
ionized or molecular ?


i was wondering if the aluminum hydroxide would be ionized or molecular, and if it was ionized what would be the percent efficiency of the electrolysis (higher or lower than molten al203/cryolite electrolysis). it it was more efficient the electrolysis could be performed above atmospheric pressure to prevent evaporation of the solution. i read al(oh)3 was soluable in ethylamine in one of those old 19th century chemistry encyclopedias.
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[*] posted on 27-8-2004 at 10:58


I strongly suspect that aluminium will displace a poton or two from ethylene diamine. I think that the strong base that everyone is going on about will act as an acid towards aluminium.

[Edited on 27-8-2004 by unionised]
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[*] posted on 27-8-2004 at 14:46


References re Al metal production and solubilities of Al(OH)3/Al2O3:

Any good textbooks of inorganic chemistry (I wish the latest version of Cotton & Wilkinson was available as a PDF somewhere - does anyone know?), Othmer's and Ullman's chemical technology encyclopedias; solubility info in Perry part 3 and the CRC Handbook.

John W.
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[*] posted on 27-8-2004 at 20:55
Al(OH)3 + ethylendiamine


Just did a quick test.
I tried to dissolve 3.6 g of Al(OH)3 (synthetic onyx, which according to the description is pure Al hydroxide) in 13.4 g (not sure, but it's 37.5 ml in total) of 99% ethylenediamine.
It didn't seem like any noticable dissolution occurred :( despite the excess being ok, and the purity too.
So maybe ethylenediamine is not the way to go :(

Admittedly it forms some sort of colloidal, but that maybe down to the fine mesh of the Al(OH)3...

[Edited on 28-8-2004 by chemoleo]




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[*] posted on 27-8-2004 at 21:55


What about freshly precipitated, i.e. colloidal, Al(OH)3, obtainable by adding an alkali e.g. NH4OH to an Al salt solution (but in insufficient concentration for there to be any redissolution as aluminate)?

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[*] posted on 27-8-2004 at 22:24


Why would a colloidal be advantageous? And why would past literature list Al(OH)3 being solubele in ethylamine? Surely, if it was only fresh AlOH3 to be dissolvable, then this would be mentioned.
Anyway - I am a bit annoyed I wasted valuable ethylenediamine for this - so I won't try again!
Btw - now, having waited for a little, the ethylene diamine has turned clear again - so no, it's not a colloidal.

PS damn - I love the smell of it though - it just smells like ammonia, yet is like a thin oil to the touch (don't repeat this)! Even fumes at the air!




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[*] posted on 5-9-2004 at 09:45
is solution conducive to electricity?


i would be interested in whether the solution of al(oh)3 in ethylene diamine is conducive to electricity and if so what is the resistance in ohms
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[*] posted on 6-9-2004 at 00:17
Why do you think so?


Quote:
Originally posted by unionised
I strongly suspect that aluminium will displace a poton or two from ethylene diamine. I think that the strong base that everyone is going on about will act as an acid towards aluminium.

[Edited on 27-8-2004 by unionised]


I think not. I would be interested in hearing why you would suspect such an anomaly. I am quite confident of the opposite effect myself, from a mechanics viewpoint.

Awaiting enlightenment.

-T
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[*] posted on 7-9-2004 at 13:50


I think it will happen because it's not rare for reactive metals to act this way. Sodium definitely will, calcium also plays the "disolving metal in ammonia" game and I think that aluminium might very well do the same.
What does mechanics have to do with chemistry?
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[*] posted on 8-9-2004 at 18:58
Reaction Mechanics


Of course I meant reaction mechanics. :)

That's an interesting opinion.
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