foxofax474
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How to practically do an addition to carbon backbone via alkyne?
In any ochem class, a standard way to extend the carbon backbone of a molecule for a synthesis question is to add a halogen to a substrate,
deprotonate an alkyne with sodamide, and connect the two via an SN2 reaction.
For instance, we can make prop-2-ynylbenzene through benzyl chloride by reacting it with sodium hydrogen carbide (at least theoretically on paper).
See https://ibb.co/HxwS55J
More generally, the reaction goes like R1-X + Na-≡-R2 -> R1-≡-R2
This works well on paper, but I haven’t found a research paper somehow or a source online that actually carries this out. Does anyone have a
practical way this reaction can be done?
For my specific example, I’d imagine it could be something like
1. dissolve NaNH2 in NH3 in a dry ice acetone bath
2. Bubble acetylene (CaC2 + H2O, passing through H2SO4 to scrub water) through it to generate NaHC2 for xyz minutes
3. warm up and dry out the ammonia, leaving a mixture of NaNH2 (which shouldnt affect the reaction) and NaHC2
I don't really know the solubility of NaHC2 in solvents since I cannot find any info on it online but I’d imagine since its a sodium salt, it should
be soluble in say polar aprotic solvents for SN2 (DMSO, DMF maybe?)
So we could say dissolve the NaHC2 and benzyl chloride in DMSO and reflux for xyzabc hours and then distill the mixture to get the product?
Does my thought process work? Anyone have any firsthand experience? Does anyone have any online references/papers on this?
Much thanks!
[Edited on 7-5-2024 by foxofax474]
(∩^o^)⊃━☆ the proof is by magic
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clearly_not_atara
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Eg:
http://www.orgsyn.org/demo.aspx?prep=CV8P0391
Acetylide is not a preferred reagent due to its extreme reactivity and the availability of alternatives in most cases (e.g. Wittig coupling, Gilman
rxn, etc). It's taught in ochem because it has a nice simple clear mechanism for pedagogical reasoning.
[Edited on 04-20-1969 by clearly_not_atara]
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Dr.Bob
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The first book below has actualy methods and preps for acetylenic chemistry, it is quite useful. The second one I have also seen, but don't know as
well.
I will agree that there are many more common ways to do some of those 2 carbon additions, many are metal based, so harder to explain, like vinyl tin
reacgents (stinky, but effective), Pd coumplings, Wittigs, etc. In modern labs, it is possible to buy many of the core compounds, and then just do
simple reactions to modify them or add pieces. Of course there are many times that you can't buy what you want, and have to buy up molecules from
small pieces, I have to do that more often than I might have thought. But the first book below is the bible of acetylene, just a newer edition than
I have (from 1971). But it has great procedures with real details.
Preparative Acetylenic Chemistry (ISSN) by L. Brandsma | Oct 22, 2013
The chemistry of the acetylenic compounds by A. W Johnson | Jan 1, 1946
Also see
The chemistry of Acetylene by Julius A. and Richard R. Vogt Nieuwland | Jan 1, 1945
The chemistry of acetylene and related compounds (Brooklyn. Polytechnic Institute. Institute of Polymer Research. Lectures on progress in chemistry)
by Ernst David Bergmann | Jan 1, 1948
Modem Acetylene Chemistry by Peter J. Stang and François Diederich | Sep 1, 1995
[Edited on 8-5-2024 by Dr.Bob]
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