Lillica
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Under what conditions should butyllithium be used at -78c?
I don't have much experience with it, but I do understand basic pyrophoric liquid handling procedures. I want to use n-butyllithium to
ortho-deprotonate a tertiary aniline. Would I need to use low temperatures in this reaction?
I've only read about low temperatures being used for one of two reasons, to either prevent degradation which would generate butane, or as a means of
thermodynamic control. Can anyone provide some insight into this?
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Metacelsus
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No, unless there are other functional groups present that might react. I've done ortho-lithiation of substituted anisoles at 0 °C, which should be
very similar to your procedure.
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Lillica
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Should I still do it at 0c for any particular reason, rather than RT? It's going to be done under argon to begin with.
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Tsjerk
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What is the solvent?
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Lillica
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The butyllithium is dissolved in hexanes, so that is what I was possibly considering using, but I am not sure if it would be the best solvent.
Metacelsus, what solvent do you find best for deprotonating anisoles? My main concern is that I just want the enolate to maintain solubility so I can
transfer it after the fact.
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Dr.Bob
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Most deprotonations are done in THF or ether, as they are better solvents for anions than hexane. You can always add the base at very low temps and
then let it rise slowly if in doubt.
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Metacelsus
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Quote: Originally posted by Lillica  | The butyllithium is dissolved in hexanes, so that is what I was possibly considering using, but I am not sure if it would be the best solvent.
Metacelsus, what solvent do you find best for deprotonating anisoles? My main concern is that I just want the enolate to maintain solubility so I can
transfer it after the fact. |
In my procedure, I used THF and TMEDA. The TMEDA might not be necessary, depending on your substrate. The BuLi I used was 2.5 M in hexanes.
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Tsjerk
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I guess the problem with room temperature is, is that your solvent will start boiling. I would at least start at zero degrees and keep the reaction on
ice. Maybe it is no problem to reach RT during the reaction but boiling solvent will give a mess.
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