SplendidAcylation
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Making sodium isopropoxide - Sodium is not dissolving
Hi
I have recently acquired some sodium metal, with which I intend to make an anhydrous superbase for use in the Stevens rearrangement.
"Sodium isopropoxide looks like fun", I thought, as I have 99.9% isopropanol;
5g of isopropanol was placed in a beaker (the beaker and pipette were oven dried beforehand)
1g of sodium was removed from oil, and dried with a paper towel to remove the oil
The sodium was then cut into thin slices, which were then put in a dry, sealed container for a short period (so that I did not have to add it all at
once)
A piece of sodium was added to the beaker, and a very slow reaction began
Very small fine bubbles emerged from the sodium
I allowed it some time to get started, as the reaction with methanol is supposedly quite exothermic, and I expected this to be similar.
After 15 minutes, the reaction was still going very slowly, so I put the rest of the sodium in.
That was about 6 hours ago; The reaction has now slowed down considerably, the sodium appears to be coated with a uniform white layer, and the bubbles
are almost invisible
The beaker, sealed with cling film, has been placed in a sealed jar containing CaCl2.2H2O pellets
I'm not exactly sure what's happening;
At first glance it seems like the sodium has been passivated by a thin layer of hydroxide or oxide, formed due to a small amount of dissolved
oxygen/water...
However, sodium oxide should react with the alcohol just as sodium does, and the hydroxide is also soluble in alcohols as far as I know.
So either way, there should be no insoluble passivation layer, as far as I can see 
Any ideas would be much appreciated
Also, if I do succeed in dissolving the sodium, I am planning to vacuum distil off the excess isopropanol, followed by rapidly transferring the solid
sodium isopropoxide to a sealed container while still hot
As far as I can tell, this should work, but there isn't much data on sodium isopropoxide, so I'm basing my assumptions on the assumed similarities to
the methoxide
Do you guys think this would work?
Many thanks
Edit: I cringed at how many times I said "as far as I can tell" or similar phrase
[Edited on 1-7-2020 by SplendidAcylation]
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draculic acid69
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What if u heat it a little bit?
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woelen
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With increasing length of the alcohol chain, the reaction with sodium becomes slower. Methanol reacts violently, ethanol still fairly vigorously,
apparently isopropyl alcohol reacts very slowly. I did indeed expect a faster reaction, but sometimes reality surprises.
Just an interesting test for you. Add some NaOH to your isopropyl alcohol. Does any of that dissolve? Solubility of NaOH in alcohols also very rapidly
decreases with increasing chain length.
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Tsjerk
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Sodium isopropoxide is not that soluble in IPA, I'm pretty sure the white substance you see is your product.
From here:
| Quote: | | For example, sodium isopropoxide is only soluble up to about 2 wt % in isopropanol |
From here:
| Quote: | The reaction was completed by heating and the mixture was refluxed
with continous stirring for a total of four hours. A light brown solution was
formed which on distillation at 80°C expelled excess isopropanol and light
brown crystals were obtained as product, yield about 85% |
where they use 2.4 grams of sodium in 100 ml IPA. Apparently you also don't need vacuum.
[Edited on 1-7-2020 by Tsjerk]
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karlos³
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You need to apply heat in the end, I always have when making both sodium (m)ethoxide.
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kmno4
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I made sodium isopropoxide several times and the worst thing one can do is refluxing IPA and Na.
During heating, Na melts and gives damned molten balls, turning around and floating for hours and very slowly dissapearing....
The best way to obtain suspension of the isopropoxide is to use Na in form of "sodium sand" (from toluene, xylene etc... see Vogel) without allowing
to melt it.
BTW. the easiest "superbase" to make is probably sodium-naphthalene radical salt. It can even (slowly) deprotonate THF, unfortunately it gives
hydrogenated naphthalene as by product and often it is just impractical... But it is easy to make
[Edited on 1-7-2020 by kmno4]
Слава Україні !
Героям слава !
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SplendidAcylation
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Thanks for the replies everyone!
Quote: Originally posted by woelen  | With increasing length of the alcohol chain, the reaction with sodium becomes slower. Methanol reacts violently, ethanol still fairly vigorously,
apparently isopropyl alcohol reacts very slowly. I did indeed expect a faster reaction, but sometimes reality surprises.
Just an interesting test for you. Add some NaOH to your isopropyl alcohol. Does any of that dissolve? Solubility of NaOH in alcohols also very rapidly
decreases with increasing chain length. |
Yes, it surprised me too.
Funny how, when you want to store sodium without reaction, it seems to react with everything, but when you want it to react... Haha
Since it reacts so slowly with the alcohol, the isopropoxide must be a strong base, I am hoping.
The pKas of methanol, ethanol, and isopropanol, are quite close together, so I don't suppose the basicity will vary too much though
| Quote: Originally posted by Tsjerk | Sodium isopropoxide is not that soluble in IPA, I'm pretty sure the white substance you see is your product.
From here:
| Quote: | | For example, sodium isopropoxide is only soluble up to about 2 wt % in isopropanol |
From here:
| Quote: | The reaction was completed by heating and the mixture was refluxed
with continous stirring for a total of four hours. A light brown solution was
formed which on distillation at 80°C expelled excess isopropanol and light
brown crystals were obtained as product, yield about 85% |
where they use 2.4 grams of sodium in 100 ml IPA. Apparently you also don't need vacuum.
[Edited on 1-7-2020 by Tsjerk] |
Yes! You were indeed spot on
Thanks for those links, it really helped to see an actual write up on it
So here's what happened;
Having left it overnight, the white layer had become thicker and somewhat fluffy, but no bubbles were visible, and a lot of the sodium remained
So I added more isopropanol, to match the ratios given in the document you sent, and I swirled it a bit
Despite this, the white stuff didn't seem to be dissolving, however some of it flaked off the sodium, leaving shiny sodium metal which still didn't
seem to react at all.
Then I applied heat, and the reaction sped up quite significantly, with most of the white solid appearing to dissolve.
Even at the boiling point of IPA, though, the reaction was by no means vigorous; it was similar to the reaction between lithium and water at room
temperature.
As the end approached, a few little bits of sodium remained undissolved, and it was necessary to maintain the solution boiling for the remainder of
the reaction, as soon as the temperature dropped a little, the reaction seemed almost to stop.
Once everything was dissolved, I was left with a slightly cloudy solution with no undissolved material.
As soon as this solution began to cool a little, beautiful needle crystals began to form
At one point I allowed it to cool to room temperature, and the whole solution solidified!
I set up a short path distillation apparatus with a 500mL RBF into which was poured the solution, boiling hot to avoid crystals forming.
As soon as the stuff had been poured from the beaker, it began to solidify on the spout of the beaker
Next time I'll make the solution less concentrated!.
Vacuum distillation then commenced, and I ended up with most (but not all) of the isopropanol recovered, and lovely white snowy crystals of the
alkoxide!
Picture to follow
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DraconicAcid
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| Quote: Originally posted by SplendidAcylation |
Since it reacts so slowly with the alcohol, the isopropoxide must be a strong base, I am hoping.
The pKas of methanol, ethanol, and isopropanol, are quite close together, so I don't suppose the basicity will vary too much though
|
Again, kinetics vs. thermodynamics. The pKas of the various alcohols aren't very different, so the basicities won't vary very much (that's a
thermodynamic property). How quickly the isopropanol reacts with the sodium is determined by kinetic factors.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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BromicAcid
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I totally relate to this! Took me 3 days of refluxing 5-7 hours a day to make like 100 grams of isopropoxide. It was just as laughably slow as you
describe. Me with a flask of sodium, adding a mL and waiting with stirring, then adding another mL, and adding heat, and thinking it was going to
take off anything second. Then 3 days later finding out that my flask is etched.
[Edited on 7/1/2020 by BromicAcid]
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SplendidAcylation
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| Quote: Originally posted by DraconicAcid | | Quote: Originally posted by SplendidAcylation |
Since it reacts so slowly with the alcohol, the isopropoxide must be a strong base, I am hoping.
The pKas of methanol, ethanol, and isopropanol, are quite close together, so I don't suppose the basicity will vary too much though
|
Again, kinetics vs. thermodynamics. The pKas of the various alcohols aren't very different, so the basicities won't vary very much (that's a
thermodynamic property). How quickly the isopropanol reacts with the sodium is determined by kinetic factors. |
Interesting again 
There is a correlation though, right?
| Quote: Originally posted by BromicAcid | I totally relate to this! Took me 3 days of refluxing 5-7 hours a day to make like 100 grams of isopropoxide. It was just as laughably slow as you
describe. Me with a flask of sodium, adding a mL and waiting with stirring, then adding another mL, and adding heat, and thinking it was going to
take off anything second. Then 3 days later finding out that my flask is etched.
[Edited on 7/1/2020 by BromicAcid] |
I know, right!
I wish I had that much sodium to turn into superbases
I suppose your flask is etched because hot sodium alkoxides dissolve glass similarly to NaOH?
Quite a few of my flasks are etched yet I can recall no reactions involving NaOH, HF, or H3PO4; its very curious.
The isopropoxide seems to have a lot of volume; I should only have 3g but it looks more like 30g
I don't think its fully dry, but I can't imagine traces of alcohol being an issue; Still, I'll probably end up trying to dry it further
Here's a pic, sorry about the low resolution
[Edited on 2-7-2020 by SplendidAcylation]
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nezza
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Try potassium. That works.
Attachment: Potassium with secondary and tertiary alcohols.mp4 (3.9MB)
This file has been downloaded 381 times
If you're not part of the solution, you're part of the precipitate.
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