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Author: Subject: Sodium hydride purification (NaH)
Monoamine
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smile.gif posted on 4-9-2021 at 08:38
Sodium hydride purification (NaH)


I'm planning on trying out a NaH synthesis that was suggested to me by a member of the forum. The advantage is that apparently it can be done at room temperature (well, outdoor temperature really, since I don't want to make H2 in a room...) by using a naphthalene catalyst.

However, this means that one is left with an n-hexane naphthalene solution containing insoluble NaH precipitate.

I wouldn't really mind just storing the NaH in n-hexane, but also having naphthalene in there just seems a bit messy.

Normally, since NaH is not soluble in n-hexane the solvent could just be filtered off, but then there would be NaH exposed to the atmosphere, which might pose a fire hazard.

The other thing I initially thought about was trying to use DMSO or DMF to extract the NaH, since these polar aprotic solvents aren't miscible with hexane. But after some research I learned that NaH in both DMSO and DMF actually poses and explosion hazard!

Another thing I can think about right now is using acetonitrile to extract the NaH, however I'm also worried that acetonitrile has the same problems as DMSO and DMF (although I couldn't find any information to confirm this). Also, acetonitrile is kind of toxic...

Lastly, might it perhaps be possible to recrystallize the NaH from THF and the n-hexane/naphthalene solution (without also crystallizing the naphthalene)?

Thank you for any input.
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[*] posted on 4-9-2021 at 11:13


I'm fairly sure that NaH would deprotonate acetonitrile.

The easy way is simply to add more hexane to dilute the naphthalene, let the solid settle, pour off the liquid.
Repeat that until you have removed most of the naphthalene.
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[*] posted on 5-9-2021 at 04:25


Thank you for the tip unionised! I will try that.

Also, I was looking at how Sigma sells NaH, and they sell it as a "dispersion" in mineral oil. What exactly is meant by " a dispersion? I couldn't find a definition of this term...

[Edited on 5-9-2021 by Monoamine]
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[*] posted on 5-9-2021 at 05:12


The powder is dispersed in the oil.

A paste.

The oil restricts the rate at which the hydride reacts with air and that makes it much easier to work with.

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[*] posted on 5-9-2021 at 21:59


Yup. Ventron used to sell LiAlH4 as a thick paste, mixed with mineral oil.

Eases your mind a little bit. It's pretty safe to work with.

At least, it used to be. I don't know if anyone offers LiAlH4 in that form anymore.
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