soma
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LAH + THF
Is there a reaction between LAH and THF? I noticed that there is always fizzing when LAH is added to THF even after there's no longer any traces of
water left in the THF.
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Nicodem
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The solvation of LiAlH4 with THF is very exothermic and should be done with extreme care, but there is no actual reaction going on.
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Dr.Bob
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There is if you don't purge the flask with nitrogen first... It usually involves a fire if doe on a large scale. Seen it once. Not a good idea,
especially if the THF is not real dry.
I would suggest always purging the empty, dry, flask with N2, then putting the THF or LAH in next, then purge the flask again carefully, then slowly
adding the other (depending on scale, for small scale, add LAH second, for larger, sometimes easier to cannulate the THF in to flask of LAH, but ONLY
if under N2.) and slowly adding the substrate as a soln in THF to the LAH slurry with good mixing. With Boranes, it is possible to react the
boranes with the THF, if refluxing, to make 1,4-butanediol. This is harder to do with LAH, but I would guess it can happen if you let it get hot
enough. Note, 1,4-butanediol is a real pain to remove from any product, being high boiling, somewhat water soluble, semi-polar and UV transparent.
It sucks.
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soma
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Quote: Originally posted by Nicodem  | | The solvation of LiAlH4 with THF is very exothermic and should be done with extreme care, but there is no actual reaction going on.
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Wondering why it is exothermic?
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Bot0nist
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Search "enthalpy change in solution" on google or wikipedia.
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