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Author: Subject: Preparation of solid aluminium isopropoxide
Klute
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[*] posted on 18-9-2009 at 18:14
Preparation of solid aluminium isopropoxide


I'm planning on trying out an Oppenauer Oxidation to prepare a few aromatic aldehydes. The most common and availble catalyst is aluminium isopropoxide.

The "classical" conditions of the Opennauer oxidation, using exces acetone as oxidant and a co-solvent, can't be used here, as the formed aldehydes xould immediatly condense with acetone in an aldol reaction. So another oxidant, non-enolizable, such as paraformaldehyde is used.

So the reaction requires solid aluminium isopropoxide in toluene to be used as a catalyst, as described in this OrgSyn prep.

So I was considering preparing the isopropoxide myself, following the details given in the preparation of alumium butoxide.
Now the problem is that usually the aluminium isoproxide is isolated by distillation, after removal of excess isoproyl alcohol. Unfortunaly, my vaccum facilities don't able me to distill this product at a reasonable temperature (bp= 140–150 °C at 5 mm Hg). And I don't feel confortable adding water to the prepared alkoxide solution to effectively filter out the impurities in the aluminium, mercury, and unreacted meatl. Actually, I don't feel confortable filtering that bloody mercury, and I'm scared the solution might be exposed to too much humidity during the filteration ( the atmosphere in my soon-to-be new lab is quite humide).

So basicly, my question is, do you think I cna use the crude alkoxide directly in the reaction? Will the mercury and undissolved impurities interfere with the oxidation?

I don't want to prepare the catalyst freshly before each run, as I plan on doing sevral small scale test, and each preparation of the alkoxide requires several hours of reflux.. So I was thinking of making a large batch and using the catalyst when needed.

Of course, all this could be simplified by simply buying commercial aluminium isopropoxide. It's cheap, and availble in 100g quantities. The problem is that "old" alkoxide is under the form of less soluble tetramer, as opposed to fresh which is a readibly-soluble trimer, so the catalyst might be less effective..
EDIT: Found a very complete document on the Oppenauer oxidation, stating that the solid tetramer can be converted to the liquid trimer by heating it, and that the two forms are equally as effective for the oxidation! Very nice read: Oxidation of alcohols to aldehydes and ketones

Basicly, I'd like to know if anyone has experience with preparing alumium alkoxides from alumium amalgam, and isolating the alkoxides. Also, if anyone have already performed a Oppenauer oxidation, even a "clasical" one, would you care to share details and comments?

Thanks in advance!

[Edited on 19-9-2009 by Klute]




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[*] posted on 19-9-2009 at 09:51


http://www.sciencemadness.org/library/books/Preparation_of_O...

Look on page 7 for an easy preparation - and the phrase "the product may be used directly for subsequent reactions" might be interesting to you! :D
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[*] posted on 19-9-2009 at 13:55


Thanks for the ref, nice book! But unfortunaly I can't use it as is, I have to remove the ispropyl alcohol if I want the reaction to occur.. The formed iPrOH (and MeOH from paraformaldehyde) must be distilled out to favor the equilibrium.



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[*] posted on 20-9-2009 at 05:26


See

https://www.hyperlab.info/inv/index.php?s=88e1ebf6d308224ea5...
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[*] posted on 20-9-2009 at 14:09


I once prepared a small amount of aluminum isopropoxide and I was able to distill a good part of it at water pump pressure. I followed the procedure in Vogels and when I distilled the excess isopropyl alcohol, crystals formed in the distillate indicating the codistillation of the isopropoxide with the isopropanol. The were highly water reactive and would react violently with water. I wonder in aluminum isopropoxide could be used instead of sodium ethoxide or methoxide as a strong base in deprotination reactions? Vogel also claims that after forming the aluminum isopropoxide, the crude material can be diluted to 1L with isopropanol and used as such for reductions. Another idea; add a small amount of water to the mixture, forming collodial alumina which will carry the mercury, and suspended impurities with it. Filter and strip the excess isopropanol with a rotary evaporator with the vacuum source protected with a calcium chloride tube and use the aluminum isopropoxide as is. I am planning on making some aluminum isopropoxide once I finish drying my isopropyl alcohol.

[Edited on 20-9-2009 by benzylchloride1]




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[*] posted on 20-9-2009 at 16:22


Aluminium isopropoxide is easily made, it was one of the first "organometallics" I made. I followed a standard procedure (I think it was Saunders & Mann), we are talking me about 14 here! I think I used I2 instead of HgCl2! So consider that! If you use a excess of iPrOH and distill that off, you could use the residual Al(iPrO)3, or use the alcoholic solution as is.

I wonder too if it could be used as a base... certainly would be much more convenient (and cheaper) than sodium (m)ethoxide for most amateurs. I suppose Al(MeO)3 maybe equally convenient, perhaps better, as a base. Can anyone get a pKa?




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[*] posted on 20-9-2009 at 17:55


All alkoxides are basic. This is dependent upon the alcohol they come from. pKa is the acidity of the conjugate acid... so.. the pKa should be ~16. Given its ability to be a reducing agent in the presence of isopropanol, it may be more difficult to control this reagent as a base. Solubility and the fact that aluminum is chelating might also be a problem. I2 is a fine way of initiating the reaction of alcohols with magnesium or aluminum.
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[*] posted on 27-9-2009 at 21:02


I am working on synthesizing some aluminum isopropoxide following the procedure in Vogels Text Book of Practical Organic Chemistry. I followed their procedure and after 6 hours of refluxing, very little of the aluminum had dissolved, but the mixture had turned quite dark. The 91% 2-propanol that I used was treated with sodium chloride and decanted from the brine that formed. The 2-propanol was then dried over anhydrous magnesium sulfate before using. The aluminum was aluminum foil cut into small pieces. 0.5g of mercuric chloride was added to the mixture. Some bubbling was observed after heating to reflux and the mixture turned very dark in color and dark spots formed on the aluminum, but even after 6 hours of refluxing, very little of the aluminum had dissolved. I am starting over with this synthesis, and drying the 2-propanol by a different way. After treating the 2-propanol with sodium chloride, I am then refluxing the alcohol with calcium oxide and distilling. What can I do to further dry the alcohol as it appears that the alcohol must be completely anhydrous for the reaction to occur?



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[*] posted on 27-9-2009 at 21:09


I use 4A molecular sieves to dry the azeotropic ethanol I distill from vodka. That should work well for polishing your IPA also I would think.

Edit: correction: I use 3A mole sieves

[Edited on 28-9-2009 by Magpie]




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UnintentionalChaos
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[*] posted on 27-9-2009 at 21:23


Quote: Originally posted by benzylchloride1  
I am working on synthesizing some aluminum isopropoxide following the procedure in Vogels Text Book of Practical Organic Chemistry. I followed their procedure and after 6 hours of refluxing, very little of the aluminum had dissolved, but the mixture had turned quite dark. The 91% 2-propanol that I used was treated with sodium chloride and decanted from the brine that formed. The 2-propanol was then dried over anhydrous magnesium sulfate before using. The aluminum was aluminum foil cut into small pieces. 0.5g of mercuric chloride was added to the mixture. Some bubbling was observed after heating to reflux and the mixture turned very dark in color and dark spots formed on the aluminum, but even after 6 hours of refluxing, very little of the aluminum had dissolved. I am starting over with this synthesis, and drying the 2-propanol by a different way. After treating the 2-propanol with sodium chloride, I am then refluxing the alcohol with calcium oxide and distilling. What can I do to further dry the alcohol as it appears that the alcohol must be completely anhydrous for the reaction to occur?


It takes a vast quantity of MgSO4 to strip out that 9% water effectively. Attached is a much simpler way to do it.

After that, you could proceed with MgSO4, reflux with magnesium turnings, or molecular sieves.

anhydrous iPrOH.jpg - 133kB




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[*] posted on 27-9-2009 at 21:45


If that paper's right, and you can even slightly overshoot the azeotrope by drying with NaOH, slow fractional distillation thereafter should get you darn near 100% isopropanol. The production of absolute ethanol is comparable. They exceed the azeotrope concentration by drying with molecular sieves and then distill again.
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[*] posted on 28-9-2009 at 02:25


Drying of isopropanol azeotrope:
Add sufficient NaOH pellets (or powder) to get 2 clear phases. Separate the phases (you can use the NaOH solution for other purposes if the i-PrOH azeotrope was pure), repeat the NaOH treatment until the pellets remain unchanged.
Distill the remaining liquid together with NaOH pellets to get a nearly completely anhydrous isopropanol.
If you need an absolutely anhydrous product, add approx. 5 mass% of sodium metal to your min. 99% product, let the metal dissolve under reflux and distill. The recovery is approx. 70%.
No need for adding an isopropylester like in the case of ethanol, because the equilibrium

NaO-i-Pr + H2O = i-PrOH + NaOH

is nearly completely on the right side of the equation. That´s why i-PrOH as a secondary alcohol is a much weaker acid than ethanol. Or you can say sodium isopropylate is a much stronger base than sodium ethylate.

[Edited on 28-9-2009 by grind]
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thumbdown.gif posted on 28-9-2009 at 07:04


I think we all know sodium metal is a great desiccant, and I also think few of us have it. Also, isopropoxide (pKa 16.5) and ethoxide (pKa 15.9) are almost the same in terms of basicity, though isopropoxide is a poorer nucleophile.

I think breaking the azeotrope with NaOH, then using magnesium metal (more reactive than aluminum) to get it anhydrous would be the way to go. OTC materials, lots of distillation, but no sodium to deal with.
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[*] posted on 28-9-2009 at 14:19


I have used the same method posted by UnintentionalChaos and grind for drying iPrOH for making Al isopropoxide:

The 91% grade is shaken with 10% of its weight of commercial flake sodium hydroxide, separated from the aqueous layer which forms, then shaken with a little more sodium hydroxide, decanted and distilled.

You can test it for residual H2O with anhydrous CuSO4.

[Edited on 28-9-2009 by entropy51]
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[*] posted on 28-9-2009 at 23:00


Do you dry the NaOH prior to use? Commercial NaOH nealry always contains as much as 10% water.
I suppose it would do no harm to the dessicant to keep it in an oven at 200degC for a while then use that?
Sure some carbonate will be formed but this can simple be filtered off?
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[*] posted on 28-9-2009 at 23:54


Quote: Originally posted by Picric-A  
Do you dry the NaOH prior to use? Commercial NaOH nealry always contains as much as 10% water.
I suppose it would do no harm to the dessicant to keep it in an oven at 200degC for a while then use that?
Sure some carbonate will be formed but this can simple be filtered off?


Why bother? It's being used as a means to strip bulk water from the alcohol by mechanical seperation of phases. A few percent water in the sodium hydroxide should be irrelevant.

Final drying should be by molecular sieves, or some other powerful means of removing traces of water.

In my experience, NaOH is consistently quite pure and reasonably dry. Why dry in an oven, when you can readily fuse it to expel water. KOH is another story entirely and is often 85% or so, and cannot be dehydrated by fusion, except to red heat, IIRC.




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[*] posted on 29-9-2009 at 01:45


Quote: Originally posted by UnintentionalChaos  
Quote: Originally posted by Picric-A  
Do you dry the NaOH prior to use? Commercial NaOH nealry always contains as much as 10% water.
I suppose it would do no harm to the dessicant to keep it in an oven at 200degC for a while then use that?
Sure some carbonate will be formed but this can simple be filtered off?


Why bother? It's being used as a means to strip bulk water from the alcohol by mechanical seperation of phases. A few percent water in the sodium hydroxide should be irrelevant.

Final drying should be by molecular sieves, or some other powerful means of removing traces of water.

In my experience, NaOH is consistently quite pure and reasonably dry. Why dry in an oven, when you can readily fuse it to expel water. KOH is another story entirely and is often 85% or so, and cannot be dehydrated by fusion, except to red heat, IIRC.


Sorry yes good point. I was confusing this with using NaOH to make anhydrous ethanol or sodium ethoxide from NaOH + EtOH
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[*] posted on 30-9-2009 at 04:31


@Arrhenius:
I didn´t know that sodium is so hard to get. Drying of solvents with sodium is so natural for me, so this idea didn´t come to me.
And of course, in this case you are right, OTC methods are better.
Houben/Weyl says drying of isopropanol with solid NaOH gives an anhydrous product which is miscible with pet ether and CS2 without a trace of cloudiness. I think such a product is satisfactory for the most "anhydrous purposes".

Another point:
With the isopropanol azeotrope at hand, you can also use K2CO3 (that should be OTC) to remove most of the water.

[Edited on 30-9-2009 by grind]

[Edited on 1-10-2009 by grind]
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[*] posted on 30-9-2009 at 18:01


*I* thinks that a very simple and scalable method is a Swern-variation, if you like names, called Albright-Goldman oxadation. It uses acetic anhydride to activate DMSO, and it is conducted at room temperature (compare to Swern!). See their JOC papers from seventies... There are couple of them IIRC...

Edit by Nicodem: I seriously hope the momentarily regression into "swiming" was some kind of a bad joke!

[Edited on 2/10/2009 by Nicodem]




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[*] posted on 30-9-2009 at 19:02


Quote: Originally posted by Sandmeyer  
SWIM thinks that a very simple and scalable method is a Swern-variation, if you like names, called Albright-Goldman oxadation. It uses acetic anhydride to activate DMSO, and it is conducted at room temperature (compare to Swern!). See their JOC papers from seventies... There are couple of them IIRC...


Swimming, are we?

Goddamnit, you should know better than that.

[Edited on 10-1-09 by UnintentionalChaos]




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[*] posted on 2-10-2009 at 15:28


OTC Isopropanol for Al Isopropoxide

Since the subject of drying IPA for the isopropoxide prep has come up, I decided to try the prep using Iso-HEET, the IPA sold as a fuel line antifreeze. The regular HEET is methanol, take note. Iso-HEET gives no color with anhydrous CuSO4, whereas 91% IPA gives a blue color indicating the presence of water, no surprise.

I ran a small scale prep of Al isopropoxide using Iso-HEET and was pleasantly surprised to see that it went essentially the same as the prep does when using IPA dried on NaOH and distilled. The Iso-HEET was used directly from a fresh, unopened bottle without further treatment. The Al was turnings from my lathe, degreased with acetone and air dried.

I thought this might be of interest to those of you who can find Iso-HEET in your local hardware or auto supply store.
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[*] posted on 2-10-2009 at 15:32


Quote: Originally posted by UnintentionalChaos  

Swimming, are we?

Goddamnit, you should know better than that.


SWIM, Swern, whatever.

If management is going to allow all manner of talk about illicit drug synthesis, the prohibition against SWIM is just plain silly.

Lighten up, otherwise the hypocrisy is palpable.

Actually the use of SWIM serves the useful purpose of identifying those with criminal intent so that the rest of us can choose to offer advice, or not, as the case may be.

[Edited on 3-10-2009 by entropy51]
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[*] posted on 2-10-2009 at 15:43


And what about swix and swij? I've seen those used recently too.

[Edited on 2-10-2009 by Magpie]




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[*] posted on 2-10-2009 at 16:08


Quote:
I thought this might be of interest to those of you who can find Iso-HEET in your local hardware or auto supply store.


That is good to hear and resonable considering it is made to aid in drying the fuel lines so excess water would be counter productive. It should be made mentioned though that a freind has recently lead me to believe that ISO-Heat has started putting an oil additive in there new formulation. They have told me that it can be seen from a yellow tint to the IpOH. Distillation is said to clear this right up though with no problem.





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[*] posted on 2-10-2009 at 16:51


Quote: Originally posted by Sedit  
Quote:
I thought this might be of interest to those of you who can find Iso-HEET in your local hardware or auto supply store.


That is good to hear and resonable considering it is made to aid in drying the fuel lines so excess water would be counter productive. It should be made mentioned though that a freind has recently lead me to believe that ISO-Heat has started putting an oil additive in there new formulation. They have told me that it can be seen from a yellow tint to the IpOH. Distillation is said to clear this right up though with no problem.


My methanol and isopropanol are from heet and iso-heet respectfully. I did distill both before use, based on their claim of an anti-rusting agent and an old report on here of a high boiling residue upon distilling heet.

I dried both with an arbitrary amount of anhydrous MgSO4 and decantation before distilling, although they seemed to have negligible water content.

I didn't boil the flask completely down and opted to scrap the last 50ml or so of a 1L run, which probably contained mostly high boilers.

[Edited on 10-3-09 by UnintentionalChaos]

[Edited on 10-3-09 by UnintentionalChaos]




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