Sciencemadness Discussion Board

Al(O-i-Pr) decomposition problem

mackolol - 23-2-2020 at 12:12

Hello members, i have a problem. I'm recently working on reduction of cyclopentanone with Al(O-i-Pr), but every time, when I try to dissolve the residue with sulfuric acid, it decomposes into cyclopentene, cause it smells like gasoline and doesn't want to dissolve. When I try to distill organic layer, it stinks with so2 a lot and leaves super harsh to remove tar. I have tried it with 50% sulfuric acid as in procedure, then in 20% freezing cold H2SO4 and still the same. Does anybody know if I can distill the alcohol straight from mother liquor, or maybe different acid?

DraconicAcid - 23-2-2020 at 14:48

If you want to avoid dehydrating the alcohol, use very dilute acid. Not even 5%.

AvBaeyer - 23-2-2020 at 19:18

The suggestion to use very dilute acid is a good one. In that case I would try dilute citric acid as it will provide an acidic workup but not so strong to dehydrate your product. Another option is to use ammonium chloride as the acid which would be even milder than the citric acid. Citric acid has the advantage that it would dissolve the aluminum ions. I am not so sure about the ammonium chloride.

AvB

Vosoryx - 23-2-2020 at 20:48

Sulphuric is also a very very strong acid, even diluted. Maybe try with a weaker (also diluted) acid if citric/ammonium chloride are too weak to break up the ppt, acetic might be a good middle ground to try, though try AvB's idea first. Add a lot of solvent to the flask, and add the acid with strong stirring to minimize "hot spots" of acid where it's concentrated enough to decompose the product.
Let us know.

unionised - 24-2-2020 at 03:14

I have heard of people using potassium sodium tartrate to dissolve the aluminium salts (at near neutral or slightly alkaline pH).

mackolol - 25-2-2020 at 09:47

Thank You very much for your suggestions. I will try it when i will have time, but this aluminium precipitate is very hard to dissolve and if forms super thick sludge that is hard to dissolve even with sulfuric acid.

Vosoryx - 25-2-2020 at 16:12

Quote: Originally posted by mackolol  
Thank You very much for your suggestions. I will try it when i will have time, but this aluminium precipitate is very hard to dissolve and if forms super thick sludge that is hard to dissolve even with sulfuric acid.


If it's a sludge then make sure to use strong stirring, especially if it ends up below the rest of the solvent.

rockyit98 - 26-2-2020 at 05:34

IT MUST BE THE acetone that formed in the reaction and left over cyclopentanone reacting to form aldols tar.heat the mix to remove acetone and use weak acid like CH3COOH.maby adding H3PO4 will precipitate AlPO4.

Meerwein–Ponndorf–Verley reduction
this is the reaction that you use Al(iPrO)3 as the catalyst
https://en.wikipedia.org/wiki/Meerwein%E2%80%93Ponndorf%E2%8...

mackolol - 26-2-2020 at 09:48

Quote: Originally posted by Vosoryx  

If it's a sludge then make sure to use strong stirring, especially if it ends up below the rest of the solvent.


I use very strong stirring, but as acid touches the surface of liquid, super thick mass precipitates, that doesnt allow stir bar to move.
Quote: Originally posted by rockyit98  
IT MUST BE THE acetone that formed in the reaction and left over cyclopentanone reacting to form aldols tar.heat the mix to remove acetone and use weak acid like CH3COOH.maby adding H3PO4 will precipitate AlPO4.

Meerwein–Ponndorf–Verley reduction
this is the reaction that you use Al(iPrO)3 as the catalyst
https://en.wikipedia.org/wiki/Meerwein%E2%80%93Ponndorf%E2%8...


Before neutralisation i boil off the acetone, till the temperature of vapors is 85C. Maybe there is some of aldol tar, but anyways after distilling this dirty organic layer, i dont even reach the b.p. of cyclopentanol, and it stinks strongly of so2

Tsjerk - 26-2-2020 at 22:04

I'm still wondering on what you are exactly doing. You didn't write anything down so far. We can't smell what you are doing over there....

mackolol - 27-2-2020 at 13:40

Quote: Originally posted by Tsjerk  
I'm still wondering on what you are exactly doing. You didn't write anything down so far. We can't smell what you are doing over there....


The reaction is called Meerwein–Ponndorf–Verley (MPV) reduction and it reduces ketones to alcohols, and vice versa.

And that's the procedure:

Into a 250ml RBF equipped with a 15cm Vigreux column and distilling condenser there's added 53mls (50g) cyclopentanone in 50mls IPA and the soln from the previous prep'n, which contains about 40g Al isopropoxide. The rxn is gently heated, which causes acetone with some water to distill off. The distillation is ended when the temp of the vapors rises to ~85°C.

The ppt inside the flask is carefully decomposed with 50% H2SO4 until acidic and saturated with NaCl. The upper layer is decanted and distilled, collecting the fraction boiling at 137-140°C. Drying with MgSO4.

The part of dissolving is the precipitate is very problematic for me as I have written above

Chemi Pharma - 27-2-2020 at 16:01

Try to clear your doubts by consulting the holy MPV bible I'm attaching below.;)

Attachment: reductions with aluminum alkoxides.pdf (3MB)
This file has been downloaded 387 times

Vosoryx - 28-2-2020 at 09:07

Next time you copy your procedure word for word from erowid, uh, don't. Some people on this forum don't mind, a lot do.

What was the outcome of the suggestions given?

mackolol - 11-3-2020 at 13:14

Today I did the procedure, but with acetic acid. The product looked way better and purer, but unfortunately I didn't manage to isolate it. Maybe tomorrow I will repeat it but with purer ketone.

I remember when one time I mixed dirty alcoholic product with excess of water to dissolve the alcohol in water and then i salted it out, the product looked quite pure, but it was too small amount for me to separate it effectively.

Maybe instead of dissolving Al in acid, I'll just dissolve the alcohol from mother liquor in water and then salt it out. It doesn't seem efficient though.

clearly_not_atara - 11-3-2020 at 17:44

I would suggest using monopotassium or monoammonium phosphate to displace the Al. According to the Hofmeister series this pushes organics out of solution (more or less...). It should improve the extraction of cyclopentanol.

Aluminium phosphate precipitates readily. I'm not sure if it will cause a problem, but I don't think it's too flocculant (unlike aluminium sulfate!)

No idea about citric acid

mackolol - 13-3-2020 at 12:34

I tried to dissolve it in 25% phosphoric acid, but it's doesn't dissolve the residue well. Acetic acid seems good for this purpose, but still i didn't get this alcohol.

After dissolving the residue and salting out the product (which was dark orange), I distilled the organic. At first some water with little bit of orange organic substance, but when i reached vapor temperature of 140C, when my product (cyclopentanol) should be distilling over, nothing came over. I let the temperature to rise next 5C forward, but then I gave up as nothing really was distilling over.

I don't know if i should use pure Al-i-PrOH instead of just mother liquor from isopropoxide synthesis or maybe should I use more isopropanol.

For now I'm angry that I do it for almost a month and have used today my second batch of chemicals needed for this reaction without success.

This MPV reduction is way more tricky, than I have thought

[Edited on 13-3-2020 by mackolol]

S.C. Wack - 13-3-2020 at 13:10

Quote: Originally posted by mackolol  
maybe should I use more isopropanol.


See page 187 of Organic Reactions volume 2. "it seems possible that dilution may improve the yields with particularly sensitive ketones such as cyclopentanone."

mackolol - 13-3-2020 at 14:23

Quote: Originally posted by S.C. Wack  
Quote: Originally posted by mackolol  
maybe should I use more isopropanol.


See page 187 of Organic Reactions volume 2. "it seems possible that dilution may improve the yields with particularly sensitive ketones such as cyclopentanone."


Thanks for confirming my suppositions. I'll try once more, when chemicals will come to me.

So, the moral is not to take procedures from erowid or just not to follow them step by step haha.

mackolol - 15-3-2020 at 06:01

Today I performed the reduction with my last bit of cyclopentanone, but I diluted it more (20ml of ketone in ~100 ml of IPA) after reduction, organic was quite pure (very light yellow in colour), but my acetic acid was over, so I used formic acid instead.

After addition of acid my organic layer turned orange and started behaving as previously, so I threw it damn away.

In organic reductions it is mentioned in organic reductions "As no appreciable condensation of this type occurs if dilute solution (approx. 0.05 molar is used", so it would mean that I need 4,25 grams of ketone per 1l of IPA...

I'll try once again, but this time distill the cyclopentanol straight from reaction. If it doesn't work, I'll reduce it with metallic sodium as described in prepchem.

[Edited on 15-3-2020 by mackolol]

mackolol - 28-3-2020 at 01:42

Yesterday I performed the reaction once again. I thought that maybe I can decompose aluminium residue with conc. NaOH solution.
Unfortunately this didn't work, but anyways the organic product was very dark coloured and impure.
All I can say is that MPV reduction is not suitable with cyclopentanone at all.

clearly_not_atara - 28-3-2020 at 03:57

The limiting factor in the MPV reduction is usually aldol condensation. Ketones are usually resistant, but cyclopentanone is uniquely prone to them. I wonder if Cu/Al2O3-catalyzed transfer hydrogenation could work with cyclopentanone and excess isopropanol:

https://s3.amazonaws.com/academia.edu.documents/45522229/Syn...

If you do it at reflux you might even be able to remove acetone as it forms.

A more ambitious thought is to make the catalyst by depositing copper oxalate on alumina and heating to decomposition. Usually oxalate decomposition gives very high surface areas.

[Edited on 28-3-2020 by clearly_not_atara]