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]

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]

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.

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]

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

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]