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Author: Subject: Alkynyl Magnesium Halide:Grignard's reagent
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[*] posted on 9-6-2019 at 09:21
Alkynyl Magnesium Halide:Grignard's reagent


Is Alkynyl Magnesium Halide a Grignard's reagent?
I mean something like ethynyl magnesium halide

If so can we use it to prepare an alkyne?rather than using Alkyl Halides
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Pumukli
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[*] posted on 9-6-2019 at 09:50


Yes, it is a Grignard.
We can prepare an alkyne from it, yes.

"rather than using Alkyl Halides"
It is a bit hard for me to understand.

Do you think of the alkyl halide -> alkene -> vic. alkyl halide -> alkyne route?

Anyway, you would need an alkyne halide at first to make that alkyne Grignard. But how could you get to the alkyne halide? Wouldn't it be easier to get to the alkyne through a different approach?
What is the target compound, if not something top secret?

[Edited on 9-6-2019 by Pumukli]
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[*] posted on 9-6-2019 at 10:54


Yeah i meant the vic.alkyl halide method

Nothing top secret:D
I was just wondering because we usually mention alkyl magnesium halide as grignard but not the alkynyl magnesium halide.

Thanks for the reply!
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[*] posted on 9-6-2019 at 13:29


Alkynyl magnesium halides aren't generally used as Grignard reagents because 1-haloalkynes aren't stable, so RCCBr + Mg --> RCCMgBr isn't feasible. You could make them using a terminal alkyne plus a regular Grignard, though....RCCH + R'MgBr --> RCCMgBr + R'H. But it's just as easy to use an alkyllithium to deprotonate the terminal alkyne.



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[*] posted on 9-6-2019 at 14:32


Why is 1 haloalkyne unstable? What will it turn into?



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[*] posted on 9-6-2019 at 15:59


Read the second sentence of this paper:

https://pubs.acs.org/doi/abs/10.1021/jo00824a003




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[*] posted on 9-6-2019 at 22:38


Quote: Originally posted by DraconicAcid  
Alkynyl magnesium halides aren't generally used as Grignard reagents because 1-haloalkynes aren't stable, so RCCBr + Mg --> RCCMgBr isn't feasible. You could make them using a terminal alkyne plus a regular Grignard, though....RCCH + R'MgBr --> RCCMgBr + R'H. But it's just as easy to use an alkyllithium to deprotonate the terminal alkyne.


In my old lab at the University of Minnesota, we regularly used ethynylmagnesium bromide, which is commercially available (you can buy it from Sigma-Aldrich). It's produced by reaction of acetylene with ethylmagnesium bromide.

However, that was the only alkynyl Grignard we used. For all other alkynes, we lithiated them with nBuLi, but doing this with acetylene would have been a bit tricky.

Also, 1-bromoalkynes in general are definitely stable. I've made quite a few (by bromination of an alkyne with NBS and catalytic silver salt in the dark). Haloacetylenes are the problem. (However, bromo(trimethylsilyl)acetylene can usually be substituted, followed by deprotection.)


[Edited on 2019-6-10 by Metacelsus]




As below, so above.
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[*] posted on 10-6-2019 at 06:42


Quote: Originally posted by Metacelsus  
Quote: Originally posted by DraconicAcid  
Alkynyl magnesium halides aren't generally used as Grignard reagents because 1-haloalkynes aren't stable, so RCCBr + Mg --> RCCMgBr isn't feasible. You could make them using a terminal alkyne plus a regular Grignard, though....RCCH + R'MgBr --> RCCMgBr + R'H. But it's just as easy to use an alkyllithium to deprotonate the terminal alkyne.


In my old lab at the University of Minnesota, we regularly used ethynylmagnesium bromide, which is commercially available (you can buy it from Sigma-Aldrich). It's produced by reaction of acetylene with ethylmagnesium bromide.

However, that was the only alkynyl Grignard we used. For all other alkynes, we lithiated them with nBuLi, but doing this with acetylene would have been a bit tricky.

Also, 1-bromoalkynes in general are definitely stable. I've made quite a few (by bromination of an alkyne with NBS and catalytic silver salt in the dark). Haloacetylenes are the problem. (However, bromo(trimethylsilyl)acetylene can usually be substituted, followed by deprotection.)


[Edited on 2019-6-10 by Metacelsus]


Thanks for the correction. I thought they were unstable as a large group.




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[*] posted on 22-6-2019 at 00:55


Quote: Originally posted by Metacelsus  
Quote: Originally posted by DraconicAcid  
Alkynyl magnesium halides aren't generally used as Grignard reagents because 1-haloalkynes aren't stable, so RCCBr + Mg --> RCCMgBr isn't feasible. You could make them using a terminal alkyne plus a regular Grignard, though....RCCH + R'MgBr --> RCCMgBr + R'H. But it's just as easy to use an alkyllithium to deprotonate the terminal alkyne.


In my old lab at the University of Minnesota, we regularly used ethynylmagnesium bromide, which is commercially available (you can buy it from Sigma-Aldrich). It's produced by reaction of acetylene with ethylmagnesium bromide.

However, that was the only alkynyl Grignard we used. For all other alkynes, we lithiated them with nBuLi, but doing this with acetylene would have been a bit tricky.

Also, 1-bromoalkynes in general are definitely stable. I've made quite a few (by bromination of an alkyne with NBS and catalytic silver salt in the dark). Haloacetylenes are the problem. (However, bromo(trimethylsilyl)acetylene can usually be substituted, followed by deprotection.)


[Edited on 2019-6-10 by Metacelsus]


Working with acetylene sucks, but you can always substitute it for TMS-acetylene, which is not a gas. But yeah, if you're already going to buy a grignard, you might as well buy directly the HCCMgX.




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