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Chemistry Forums for Students => Organic Chemistry Forum => Organic Chemistry Forum for Graduate Students and Professionals => Topic started by: ocvihwer on December 09, 2016, 11:54:20 AM

Title: Washing NaH (60% suspension in mineral oil)
Post by: ocvihwer on December 09, 2016, 11:54:20 AM
Background: I'm working on a Wittig reaction and I'm using NaH (60% suspension in mineral oil) to deprotonate

My product is very nonpolar and the grease in NaH might be a problem for workup. So I tried to use freshly distilled THF to wash away the grease. I add some THF to NaH/oil suspension and removed the liquid, hoping that THF will dissolve the grease away.

However, I cannot remove all the THF from the NaH solid. I decided to just leave it in there and added DMSO anyway.

Question:

Will the residual THF pose any potential problem?

Thanks!
Title: Re: Washing NaH (60% suspension in mineral oil)
Post by: rolnor on December 09, 2016, 03:06:49 PM
I have worked with methylenetriphenylphosphorane and that reagent was in the original paper made with NaH/DMSO. I found that it can be generated with n-BuLi/THF instead wich I find more convenient.
To answer your question, no, THF will not be a problem.
Title: Re: Washing NaH (60% suspension in mineral oil)
Post by: Dan on December 10, 2016, 03:28:25 AM
Absolutely agree. DMSO is a total hassle, BuLi or tBuOK in THF is much more convenient.
Title: Re: Washing NaH (60% suspension in mineral oil)
Post by: RedViper9 on January 21, 2017, 03:08:07 AM
Assuming your THF is dry, it should not be a problem (See Williams and Lawton JOC, 2010, 8351. (http://pubs.acs.org/doi/abs/10.1021/jo101589h)); however, I've always triturated NaH with dry hexane or dry pentane (very flammable!) since the trace solvent is inert and is easily removed after the reaction.
Title: Re: Washing NaH (60% suspension in mineral oil)
Post by: pgk on January 21, 2017, 01:21:58 PM
I have used NaH (from mineral oil suspension) in diethyl ether, as a reaction medium. I have got better yields by preliminary washing NaH with petroleum ether (anhydrous, by keeping  over molecular sieves 3-4 Å), followed by washing with diethyl ether than washing with diethyl ether, only.
Title: Re: Washing NaH (60% suspension in mineral oil)
Post by: discodermolide on January 21, 2017, 03:20:33 PM
You used to be able to buy 100% NaH from Aldrich.
Title: Re: Washing NaH (60% suspension in mineral oil)
Post by: RedViper9 on January 21, 2017, 03:51:53 PM
Quote from: discodermolide on January 21, 2017, 03:20:33 PM
You used to be able to buy 100% NaH from Aldrich.

Is this similar to 60% H2O2? I expect in both cases Sigma would be happy to sell it to you, but the DoT won't ship it.

On a side note, has anyone used the KH suspended in a solid wax block?