vinothan23
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Want to use lithium inplace of Butyl lithium
I want to use Lithium metal inplace of butyl lithium for the reaction i have attached. kindly suggest me will it work or not. And i also want to know
why people use Butyl lithium not Lithium metal even though lithium is much cheaper than Butyl lithium.
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[Edited on 23-10-2012 by vinothan23]
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UnintentionalChaos
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I don't see how using Li metal would work. Li is a reducing agent, BuLi is a very strong base, and based on the mechanism shown, you need to metallate
the benzene ring, a job for an alkyllithium base. The Li-O coordination is also clearly important so another metal would not stand in as well.
Lithium metal would do one-electron reductions and make a mess.
You can substitute another alkyllithium, but metallic lithium won't get you anywhere.
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'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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vinothan23
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Bt Sir Li is also a very strong base....
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Hexavalent
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Yes, but it would do single-electron reductions as it itself has only one valence electron, making a mess of your reaction. The intermediate 'II' also
suggests you need the alkyl group. If you are attempting a synthesis like this, then you should probably be able to work out questions like these
yourself.
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
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Nicodem
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Lithium is not a base. It is a metal. For obvious reasons, it can not be used in such directed ortho-lithiations.
If you have lithium, then why don't you just use it to make n-BuLi? Nevertheless, I suggest you avoid organolithium chemistry until you learn some
basics. When working with pyrophoric materials, lack of knowledge can cause lack of life.
PS: Please open threads without references only in the Beginnings section. Read the forum guidelines for more information on how to properly open
threads. Also, do not attach Word files for pictures, or any other file format that requires external viewers. Attach a picture instead.
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scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
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Nicodem
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Thread Moved
23-10-2012 at 11:54 |
vinothan23
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I am using sodium, potassium, sodium hydride and butyl lithium from last four years i mean i have good enough experience in working with pyrophoric
materials. I have used sodium metal for amide deprotonation (HUNTERA ND JONESJ,. Chem. SOC.9,4 1 1930 ). But in picture butyl lithium is used. My
worry is about aromatic deprotonation ( second deprotonation, see picture). We know that phenyl lithium is prepared by lithium metal why i cant i use
lithium here.
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Nicodem
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Quote: Originally posted by vinothan23  | | But in picture butyl lithium is used. My worry is about aromatic deprotonation ( second deprotonation, see picture). We know that phenyl lithium is
prepared by lithium metal why i cant i use lithium here. |
BuLi is not needed for the deprotonation and lithiation of the amide (LiH could do that as well), but is needed for the directed
ortho-lithiation. What you call a "second deprotonation" is obviously not that. That reaction is called "directed ortho-lithiation" and
requires an alkyllithium, LDA or LiTMP. If you check its reaction mechanism, you will immediately see why lithium cannot be used.
And phenyllithium is prepared from lithium and a halobenzene, which is something very different. It can't be prepared from lithium and benzene, but
can be made by letting BuLi react with benzene.
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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