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Author: Subject: Cutting sodium
sveegaard
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[*] posted on 8-8-2014 at 06:55
Cutting sodium


Hi guys

I wanted to hear if any of you have experience in cutting sodium with a minimum amount of oxidation?
I'm making some reactions where I need elemental sodium. I take a slab from the chemical stock room (I currently work at a university), cut a piece off and try to cut off all the oxide/hydroxide layer while under pentane. This is followed by a wash in fresh pentane and then it is transferred to an argon flushed flask. Trouble is, the reaction doesn't seem to work well, although it is a published method. My work is confidential, but I can tell that the first step involves a reaction with sodium and another chemical, helped by phenanthrene in dimethoxyethane or THF. The sodium reacts very sluggishly, so I suspect I somehow get a thick oxide layer on my sodium.

Am I really that retarded at weighing out sodium, or...?
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TheChemiKid
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[*] posted on 8-8-2014 at 07:04


You could cut the sodium under an inert solvent, preferably one more dense than sodium. After you cut it, add a small amount of isopropanol, or other longer chain alcohol, do not use methanol or ethanol. This will help clean the surface by forming a small quantity of sodium alcoxide in solution, cleaning the surface.



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forgottenpassword
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[*] posted on 8-8-2014 at 07:10


It would be the lack of surface area that is the problem. You could make birdshot sodium or sodium wire.
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TheChemiKid
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[*] posted on 8-8-2014 at 07:15


Just slicing sodium thinly can give very similar results to sodium wire.



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Magpie
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[*] posted on 8-8-2014 at 15:29


I recently made sodium ethoxide from sodium and absolute ethanol. My sodium is in large sticks about 1" square by ~3", covered in some kind of viscous oil. I cut the oxidized sides off one stick. From the stick I cut some small cubes about 1/4" (6mm) on a side. I removed oil from these cubes by paper towel just before dropping them down my reflux condenser into the ethanol, per procedure. This worked well and my sodium steadily reacted with no addition of external heat.

[Edited on 8-8-2014 by Magpie]




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mnick12
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[*] posted on 8-8-2014 at 15:50


Well it doesn't sound like its and oxide/passivating layer problem. If it were it would be obvious from the tarnished metal. Are you sure your reagents are pure? Additionally if it is a published procedure could you give a reference for it? That would help, otherwise we are just taking shots in the dark.
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Mailinmypocket
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[*] posted on 8-8-2014 at 16:27


At work we prepare very fine sodium by sticking sodium into a reflux set up under xylene and heating it up to melt the sodium, then it is stirred rapidly and very small globules of sodium are created. Stop heating and keep stirring and when cool you have very fine sodium. It does make exceptionally reactive sodium- Might not be something to try right from the get-go though.
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Dr.Bob
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[*] posted on 8-8-2014 at 18:44


Yes, if you just cut off a piece and scrap off any crud, it will be fine. You could cut it into small pieces in some mineral oil, and then just rinse it with hexanes before use. I would not do the boiling xylenes thing unless you have to, that is very exciting, and not ideal for new chemists. Using a press and die, you can extrude sodium wire, which is great for stills and hard to run reactions. But that can be dangerous, as if you have any spill or if you try to quench the leftover sodium, it can react quite violently or start a fire.
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[*] posted on 10-8-2014 at 21:49


I really like Mailinmypocket's sodium globules. If you consider it, even with a sodium wire, there's still a good bit of unreacted sodium in the core. Then again, a sodium wire could be cut into little bits with a spatula under oil.



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sveegaard
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[*] posted on 11-8-2014 at 03:54


Thank you for all your replies!

I think it turns out I might have been too sloppy about moisture/oxygen. Tried the reaction again today, but with a Schlenk line, and it immediately turned green on the addition of solvent. The sodium still got a thin layer of oxide/hydroxide, possibly because 1) the pentane I used was not completely dry and 2) when the pentane evaporates, water condenses on the pliers (oops). Never thought too much about that.

And btw, I don't see myself as new to chemistry although I got my MSc in Chemical Engineering as recently as last year :)
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