Sciencemadness Discussion Board - Preparation of solid aluminium isopropoxide

Preparation of solid aluminium isopropoxide

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Pumukli - 19-5-2015 at 04:11

On the basis of this sentence:

"For many purposes it is unnecessary to distill the reagent and the dark solution obtained on dissolution of the aluminium can be used directly."

This was copied from the remarks of the isopropoxide synth. procedure I found in the Hilgetag book.
As I wrote I never tried this reaction (except once decades ago but not remembering practically anything meaningful about that synthesis) but I assumed the original authors wrote that sentence because they saw it was dark.

byko3y - 21-5-2015 at 14:22

Ok, so after standing for 2-3 days, the mixture of aluminium turnings + iodine + isopropanol + some more stuff I've tried to use as a catalyst turned less orange-red, almost colorless, so I tried distilling it. I recovered almost quantitively the isopropanol I've charged into the reaction, and detected almost no reacted aluminium. Can't say precisely, but it's very small amount, close to my measurement error.
Most likely some really strong agitation and long reaction time is needed to get all the aluminium reacted, because clearly the iodine by itself is not able to destroy the protective aluminium oxide layer at low temperature, and strong agitation destroys the layer mechanically. But in this case do I need the iodine at all? If it all depends on mechanical force, why do I need anything else?
Few more researchers that failed with iodine in isopropanol:
http://images.library.wisc.edu/WI/EFacs/transactions/WT1896/...
and
http://archive.org/stream/philtrans07558607/07558607_djvu.tx...
I'd like to quote the aluminium alcoholates that were successfully prepared by the last researchers: ethylic, propylic, iso-butylic, amylic, benzylic, phenylic, cresylic, and thymolic.
No methanol, no isopropanol, sorry.

[Edited on 22-5-2015 by byko3y]

blogfast25 - 21-5-2015 at 18:29

Quote: Originally posted by byko3y

But in this case do I need the iodine at all? If it all depends on mechanical force, why do I need anything else?

Cos G-men are f*cking up your speriments?

WGTR - 21-5-2015 at 19:19

Quote: Originally posted by byko3y

Ok, so after standing for 2-3 days, the mixture of aluminium turnings + iodine + isopropanol + some more stuff I've tried to use as a catalyst turned less orange-red, almost colorless, so I tried distilling it. I recovered almost quantitively the isopropanol I've charged into the reaction, and detected almost no reacted aluminium. Can't say precisely, but it's very small amount, close to my measurement error.
Most likely some really strong agitation and long reaction time is needed to get all the aluminium reacted, because clearly the iodine by itself is not able to destroy the protective aluminium oxide layer at low temperature, and strong agitation destroys the layer mechanically. But in this case do I need the iodine at all? If it all depends on mechanical force, why do I need anything else?

What I wonder, is where your iodine is going. Are you able to recover it? The solution I have is still sitting quietly on the table, either muddy brown, purple, or green, depending on how one looks at it. Is it possible that your iodine is subliming away during the reaction? I don't understand how your solution is going colorless otherwise under those conditions.

byko3y - 21-5-2015 at 21:32

Probably the whole iodine reacted with aluminium and turned into AlI3, which is not capable of peneterating Al2O3 layer at this conditions (80°C, IPA). Actually, I needed to add some copper salt to force the solution color to change, because without it even after 3 hours of heating and mild agitation I could not see any changes. There was a slight turbidity in the solution, but it was mostly clear.
The slight yellow color of the solution most likely comes from some high boiling yellow compound, which I was able to distill from the mixture (0.5 ml out of 35 ml IPA charged). AFAIK, if this was isopropoxide, it would hydrolyze rapidly, but I see no Al(OH)3, only a clear yellow oil.
After distillation of any volative products, I quickly washed the aluminium turnings with hydrochloric acid to remove water soluluble solids. The resulting solution after some heating turned yellow, however I don't know why.
And by the way, when I charged a 13% solution of HCl into non-reacted aluminium turnings (so it would be easier to remove them through a narrow flash neck), noticable reaction(bubbling) started even at room temperature, and after reaching something like 50-60°C the reaction became really vigorous. So I'd say my aluminium has good reaction ability, but the IPA-I2 conditions led to an extreemly sluggish reaction.

WGTR - 24-5-2015 at 18:36

I should mention that every day or two I go by and release pressure from the vial. Cracking the seal evidences a slight "hiss" as pressure is released. I'm not even bothering to heat the material, it's just sitting quietly at room temperature. It's definitely a slow reaction at these temperatures.

When I first pick up the vial after letting it sit for a day or so, I notice that there are considerable amounts of gray powder mixed in with the remaining shiny aluminum powder. I'm going to let this reaction sit quietly in the corner. I plan to check on it periodically.

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