[owk9688]

Hi all,

I'm doing a deprotonation of an alcohol in THF with sodium hydride to evantually yield an ether after the alkoxide attacks a primary bromoalkane. Ive never used NaH before but I've read it is insoluble in every solvent it does not react with (deprotonate). I'm wondering how can NaH be so efective as a base if it never is solubilized; I guess I'm confused as to how my compound (soluble in THF) will ever be able to come in contact with the NaH that is outside of solution.

Thanks for any *delete me*

[discodermolide]

There are many heterogeneous reactions in organic chemistry, hydrogenolysis being probably the most common.
Think about reactions on a surface.

[kriggy]

Also, it is not 100% insoluble. SOme of it will disolve and deprotonate the alcohol forming alkoxide and hydrogen gas that escapes. Then more of NaH gets dissolved.

[wildfyr]

Kriggy is right. Also, if you've never used NaH before please be careful, it can be quite dangerous. Is it the type that is suspended ~50%by by in mineral oil? This oil will affect your workup. It is possible to remove it beforehand but it makes the NaH more pyrophoric.

[owk9688]

This is my first time using NaH and yes, it comes in a small can saying 60% dispersion in mineral oil. I was planning on weighing it out (taking into account the oil too) in a RBF, adding in a large volume of hexanes, swirling it a bit under nitrogen and then removing the remaining liquid via syringe or a cannula before evacuating the flask and re-filling it with Nitrogen. I think that should be safe, right?

Thank you for the bit on surface catalysis. I hadnt thought about surface reactions much, especially not for simple acid base deprotonations. I'm assuming the surface would be the NaH crystal lattice itself?

[wildfyr]

Yes, that is a standard way to clean the oil off. If you need to get truly all the mineral oil off, it should be washed 3 times. I would only pull vacuum on the last one, and do it slowly and carefully so the powder doesn't jump all over the place. Remember that at this point that powder is HIGHLY pyrophoric. I would quench this reaction with something like slow addition of isopropanol, then MeOH, then add whatever your aqueous workup is.

For your lattice question, I'm not sure I understand. The outer surface has exposed hydride groups, and as these react /dissolve, more hydrides are exposed and so on. It probably does proceed along crystal boundaries to some degree.