Sciencemadness Discussion Board

Synthesis, storage of sodium ethoxide

monolithic - 12-8-2020 at 04:08

I need some sodium ethoxide. I've seen a few different preparations and it seems the NurdRage synthesis is the cheapest and easiest: anhydrous ethanol + NaOH + molecular sieves into a single neck flask. Seal from atmosphere and allow swirl every now and then until the solvent line no longer falls.

I would like to separate the solid sodium ethoxide for purification and calculation of yield. I'm not familiar with how water/air sensitive sodium ethoxide is. Can I simply vacuum filter the sieves, rinse them with some dry ethanol, and then distill the ethanol to dryness to yield solid sodium ethoxide?

I also read an old Nicodem post about precipitating sodium ethoxide directly from the reaction mixture with acetone anti-solvent, to avoid distillation. Has anyone tried this -- did you see any self-condensation of acetone?


Is there an ideal recrystallization solvent for sodium ethoxide? How long can it be stored as a solid, in a sealed bottle in a freezer until it degrades?

walruslover69 - 12-8-2020 at 05:01

I have only ever synthesized it from sodium metal and ethanol and then pulled a vacuum to remove excess ethanol. You should be fine with vacuum filtering though.

as long as NaOH isn't a huge problem for you, there is a decent chance that you will create more impurities by recrystallizing due to air exposure than you will remove.

In a sealed container It should be stable for quite a long time. In my lab I have a rubber septa capped RBF with several grams of ethoxide that is roughly a year old, it has developed a little bit of yellow color, but still looks better than the almost orange 98% sodium ethoxide I have ordered from Sigma. Storing it in the fridge might also be counterproductive as the condensation from taking it out might cause more damage than storing it at room temp.

B.D.E - 12-8-2020 at 08:36

Never tried the method you've decscribed, but I have made some sodium alkoxides in the past by adding sodium metal into some heptane, followed by the addition of the alcohol. The alkoxide salt ppt right away as a fine white powder(soaked with the heptane of course).

Most(if not all) saturated hydrocarbons should work.

[Edited on 12-8-2020 by B.D.E]

karlos³ - 12-8-2020 at 10:22

I have heard the method with NaOH isn't that reliable, and if it even works then it will be low yielding.
Don't want to discourage you though.

But if you can obtain some Na metal, using this it is very straight forward to synthesise both NaOEt and NaOMe.
I prefer the latter though, as MeOH is usually much drier straight from the can.

You simply prepare an ice-salt bath with your flask or beaker seated in, containing the dry alcohol.
Then you add the sodium in small pieces, in successive portions.
It will be somewhat exothermic initially, of course, but at some point when all the sodium has been added, the reaction will slow down quite quickly.

Actually, the ice-bath can be removed after an half hour or so, likely even earlier(as long as you're not working with like, 20g of Na or such), let it get to RT then(or for faster results, apply a warm water bath).
There will be quite a lot of residual sodium floating around at that point, visibly shrunken, but they aren't bubbling as vigorous, or much at all, as they did at first when added.
When it is warm, you probably need to reflux it for a short time until these little residues have reacted as well.
If you need the alkoxide isolated, you can already set it up for distillation at this point, the last few pieces will have reacted probably even before the first drop of alcohol comes over.
Although, I have never isolated either of the alkoxides, when I made and used them it was always for some reaction that was done in the alcoholic alkoxide solution directly.

But if you use sodium metal, you don't need to isolate it really, as the yield will be quantitative anyway in regard of the Na used.
I wouldn't recommend to try to get the NaOH method to work, it is not reliable and will likely result in unneccessary frustration.
Instead I would recommend to acquire some Na metal, using this for alkoxide production is very straight forward and it is very likely to work just as it should on the first trial.
Just my opinion on this.


Maybe the attached paper is also useful for you?
It describes the formation of potassium methoxide from K2CO3/KHCO3 in dry methanol.
I've heard it works better with potassium, also with KOH and dry alcohol, than with NaOH, but I can't add much else.
Never looked into this reaction really, I simply prefer to use the alkali metals directly.

Attachment: platonov2002.pdf (27kB)
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monolithic - 12-8-2020 at 17:26

Will take a look at that paper, thank you. I would prefer to take the simple and high yielding approach that you mentioned, just adding sodium to ethanol, but I haven't had much success with sodium synthesis and it's rather expensive to purchase. Plus it's fun to experiment with alternative approaches. :)

karlos³ - 12-8-2020 at 17:53

If I would have to make sodium metal myself, I would definitely try the exciting looking method of nurdrage, it doesn't even look that complicated, the one in dioxane, by reaction of NaOH and magnesium?
I get the impression if done just the right way, that while it might be a good bit of work, it will work well enough to get at least some metallic sodium.
But I might be wrong.
I would definitely try this method if I would have to make the sodium for myself.

monolithic - 19-8-2020 at 10:48

I took a very lazy approach, just to see if it would work.

Approximately 55 g 190 proof grain alcohol + 11 g NaOH + 60 g 4A sieves into a flask. Stirred until all NaOH was dissolved, then stoppered and let sit for about 40 hours with occasional swirling. Vacuum filtered to yield maybe 20 ml of a yellow syrupy solution which was diluted with 100 ml dry acetone. (The 4A sieves adsorbed a large amount of the ethanol.) The solution turned cloudy and white, and a small amount of precipitate was visible on the bottom of the beaker. This was placed into a freezer for 30 mins to further precipitate any sodium ethoxide... then the white cloudiness disappeared to yield a clear light yellow solution. I was left with a very small amount of white solids floating on top. Not really sure what happened, but I guess that's what happens when you're lazy.

I'll be more thoughtful with my next approach, by drying the ethanol separately. I plan on trying the sieve method once more with 3A sieves rather than 4A. If that doesn't work then the NaOH separatory funnel method shown here http://www.sciencemadness.org/talk/viewthread.php?tid=2656 will be attempted. And if that doesn't work then I'll resolve myself to getting the NurdRage sodium synthesis to work, and make sodium ethoxide that way!

[Edited on 8-19-2020 by monolithic]

macckone - 19-8-2020 at 11:10

4A sieves are not suitable for drying methanol, ethanol or acetone.

https://www.bio.umass.edu/microscopy/mol_sieves.htm

dry the alcohol first then add dry hydroxide with 3A sieves.

S.C. Wack - 19-8-2020 at 17:47

Alkali won't play nice with acetone and likely the sieves as well. It's been said for over 15 years that the acetone patent won't work, and effort is best directed towards obtaining sodium. I note that in the vague sieve patent (US3479381) they prepare ethanolic 0.1M NaOH, add 4A sieves, and allegedly find 0.1M Na ethoxide. They do not say what the analysis is without adding sieves!!!! Probably quite close to that if protected from air.

An azeotrope patent might work, but for ethoxide it uses benzene...a lot of it IIRC. PS btw the azeotrope is 74.1% benzene, but something automatic can be rigged up using lime. Not sure what advantage there is to benzene over anhydrous alcohol.

[Edited on 20-8-2020 by S.C. Wack]

monolithic - 20-8-2020 at 03:52

Quote: Originally posted by S.C. Wack  
Alkali won't play nice with acetone and likely the sieves as well. It's been said for over 15 years that the acetone patent won't work, and effort is best directed towards obtaining sodium. I note that in the vague sieve patent (US3479381) they prepare ethanolic 0.1M NaOH, add 4A sieves, and allegedly find 0.1M Na ethoxide. They do not say what the analysis is without adding sieves!!!! Probably quite close to that if protected from air.

An azeotrope patent might work, but for ethoxide it uses benzene...a lot of it IIRC. PS btw the azeotrope is 74.1% benzene, but something automatic can be rigged up using lime. Not sure what advantage there is to benzene over anhydrous alcohol.

[Edited on 20-8-2020 by S.C. Wack]


I ended up throwing the sieves away, they didn't look right even after repeated water and dilute acid washings. What patent are you referring to with 'acetone patent'? US3479381?

S.C. Wack - 20-8-2020 at 13:46

It's mentioned if not attached in the relevant thread, the long kind of thread where posts are best posted IMHO instead of everyone needing their own personal thread on each subject each week. The fact that acetone produces visible results and is patented does not mean it is worth exploring.

morganbw - 20-8-2020 at 14:03

I have only had a need for NaOEt and/or NaOMe a few times and always used the metal to get to it. I have several pounds of sodium metal and it will probably last as long as I live. @len1 gave a very nice write up on getting sodium medal in the Prepublication forum. I worked using electricity to cause chemical transformations so this would be my method.
Nurd Rage has presented a non electrical method which should be good as well.

B.D.E - 21-8-2020 at 06:35

Just saying that producing sodium is quite fun as well.
Also, lithium is quite cheap(per mole) on ebay, if you can find use in LiOEt/LiOMe.

[Edited on 21-8-2020 by B.D.E]

unionised - 21-8-2020 at 11:00

From time to time I have wondered about this:

Mg + 2 EtOH -->Mg(OEt)2 + H2

Mg(OEt)2 + 2 NaOH --> 2 NaOEt + Mg(OH)2

Has anyone ever tried it?

macckone - 21-8-2020 at 11:32

unionised,
See nurdrage's series on sodium production via alcohol catalyzed reaction with magnesium.

monolithic - 21-8-2020 at 11:52

Quote: Originally posted by unionised  
From time to time I have wondered about this:

Mg + 2 EtOH -->Mg(OEt)2 + H2

Mg(OEt)2 + 2 NaOH --> 2 NaOEt + Mg(OH)2

Has anyone ever tried it?


https://www.youtube.com/watch?v=BsNoiFj3wlw

A large and strong stir bar is important, otherwise the magnesium will aggregate and create a hot spot which cracks flasks (from experience.)

S.C. Wack - 21-8-2020 at 12:53

Quote: Originally posted by unionised  
Mg(OEt)2 + 2 NaOH --> 2 NaOEt + Mg(OH)2


You knew 15 years ago it's not very soluble. The Ca version may be more soluble, but that's not how I'd use Ca here. The Mg could take the place of lime as a drying agent instead.

[Edited on 21-8-2020 by S.C. Wack]

unionised - 21-8-2020 at 13:23

Quote: Originally posted by S.C. Wack  
Quote: Originally posted by unionised  
Mg(OEt)2 + 2 NaOH --> 2 NaOEt + Mg(OH)2


You knew 15 years ago it's not very soluble.

[Edited on 21-8-2020 by S.C. Wack]

Well, I did say "From time to time ".
IPA might work better.

The thing is that I can buy magnesium more or less in bulk.

unionised - 21-8-2020 at 13:25

Quote: Originally posted by macckone  
unionised,
See nurdrage's series on sodium production via alcohol catalyzed reaction with magnesium.

Why?
I can (If I'm lucky) do two nice quiet; well behaved; near quantitative, reactions and get a solution of sodium alkoxide in alcohol.

S.C. Wack - 21-8-2020 at 21:37

Quote: Originally posted by unionised  
The thing is that I can buy magnesium more or less in bulk.

And you can reduce NaOH with it in seconds, then add ethanol to the residue.

unionised - 22-8-2020 at 02:47

Quote: Originally posted by S.C. Wack  
Quote: Originally posted by unionised  
The thing is that I can buy magnesium more or less in bulk.

And you can reduce NaOH with it in seconds, then add ethanol to the residue.

"And you can reduce NaOH with it in seconds"
With a loss of about 80% of the product, and my eyebrows (or worse) if I'm not careful.
It's not that I don't like fireworks, it's just that they aren't generally very well controlled / high yield reactions.
The idea of doing it using menthol as a solvent/ catalyst is more appealing but I still wonder if the pair of reactions I wrote, (or the equivalent with IPA) would work.

S.C. Wack - 22-8-2020 at 15:56

Quote: Originally posted by unionised  
"And you can reduce NaOH with it in seconds"
With a loss of about 80% of the product, and my eyebrows (or worse) if I'm not careful.
It's not that I don't like fireworks, it's just that they aren't generally very well controlled / high yield reactions.


Well that's fair NurdRage only gets 41% yield of actual clean sodium from 3 parts Mg to 4 parts NaOH with a soup can and a brick, no doubt his yields would be much less if he was only trying to make ethoxide.

B.D.E - 25-8-2020 at 21:30

Quote: Originally posted by unionised  
Quote: Originally posted by S.C. Wack  
Quote: Originally posted by unionised  
The thing is that I can buy magnesium more or less in bulk.

And you can reduce NaOH with it in seconds, then add ethanol to the residue.

"And you can reduce NaOH with it in seconds"
With a loss of about 80% of the product, and my eyebrows (or worse) if I'm not careful.
It's not that I don't like fireworks, it's just that they aren't generally very well controlled / high yield reactions.
The idea of doing it using menthol as a solvent/ catalyst is more appealing but I still wonder if the pair of reactions I wrote, (or the equivalent with IPA) would work.

I got 50% yield of clean sodium metal. It probably would have been about 55~60% if weren't the purification steps followed. And I think you can just use the aggregate "as is" for the purpose of making alkoxides.

Also, 20% yield is still probably more than you're gonna get with your method, so I wouldn't be too upset about the sodium yield(additionally this way you'll get a much purer product[given thay you'll use excess Mg/purify the sodium with dioxane]).

And the reaction isn't as uncontrollably dangerous as you might think. j
Just use one of these birthday cake sparklers as a fuse and immediately cover the top of the can "completely" with a heavy street tile (the hydrogen will find it's way out, just make sure to use heavy enough tile or else it'll fall).

Here's me starting the rxn by just throwing a piece of burning magnesium in. I've added a layer of magnesium sheaving only(without NaOH) on top of the rxn mix as a replacement for a fuse(not recommended):

Attachment: VID_20190630_121950.mp4 (6.5MB)
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It's easy, fast and spectacular.
---

Just as a side note, when using KOH instead of NaOH, the reaction is much more robust and dangerous. Also from my experience, the potassium metal would not separate by heating with dioxane.

[Edited on 26-8-2020 by B.D.E]