soma
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purification of LAH
Not sure if this is the right place for this - but since LAH is used alot in organic chemistry, I thought to post here.
Anyone tried purifying LAH? (LiAlH4)
I've noticed that it reacts more quickly and at lower temperatures when pure.
Would appreciate information on purification - recrystalization - methods.
Thanks.
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RiP057
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I know this sounds lame, but buy more if its been sitting around for a while....
story of mine is that I had a whole mess of it 10g in a round bottom covered in ether. well it wasnt the cleanest and the smallest spatula full of
fresh LiAlH4 made the whole thing erupt and I had an ether fire
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Fleaker
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Anyone think of looking in the references section for W.L.F. Armarego's Purification of Laboratory Chemicals (or Brauer's for that matter, ought to be
in there)?
Neither flask nor beaker.
"Kid, you don't even know just what you don't know. "
--The Dark Lord Sauron
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soma
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Not sure how to get to the references section. When I try to get there I get a message that I don't have permission to view it.
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madscientist
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Thread Moved
17-4-2011 at 15:15 |
soma
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It's not in Armarego. I'll check Brauer --
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soma
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Brauer has preparation methods but not purification.
Thanks for the suggestions.
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Mumbles
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Whenever we need exceptionally pure LAH in the lab, we extract it with ether a few times, and filter off the insolubles. Evaporation of the solvent
gives white LAH. Most of the good stuff comes over with the first extraction, but if you want it all 3-4 times does the trick. The grey solid
remaining works fine for most reductive applications, but for the sensitive stuff and some specific reactions, the pure and totally soluble form is
nice.
Be forewarned, that you need to get ALL of the ether out of both the white and grey products, or they will catch fire when/if exposed to air, so this
needs to be done under inert atmosphere. A glovebox is nice for this, but probably not necessarily available to all home chemists.
Typically, you only get 20-30% of the clean stuff out, just FYI.
[Edited on 4-21-2011 by Mumbles]
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