How does Grignard work with Alkynes?

C

cuttiedentist

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• Jul 26, 2007

• #2

dsony2284 said:

Does anyone know what a grignard CH3MgBr with an alkyne would do?

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grignard reagent remove any acidic H so it would do the same this as it does with other Hs.
i guess this is correct, sorry if im not

 

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D

dsony2284

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• Jul 26, 2007

• #3

but theres no acidic H in an alkyne without an O, right? So what would happen here since there is no acidic hydrogen

 

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R

RING12

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• Jul 26, 2007

• #4

dsony2284 said:

but theres no acidic H in an alkyne without an O, right? So what would happen here since there is no acidic hydrogen

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the H next to triple bond is acid too.

 

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drteeth

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• Jul 26, 2007

• #5

The triple bond has a high electron density and slightly attracts the H's electrons. This makes the H slightly more acidic then say that of an alkane. The strongly basic Grignard would steel this H. So the CH3(-)MgBr would become CH4...

 

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Q

quikag1

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• Jul 26, 2007

• #6

Its another way to make an alkanide ion. Every1 else was correct in that it does pull off the acidic hydrgogen from the triple bond, but the main product of the rxn is the alkanide ion.

 

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shane.

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• Jul 26, 2007

• #7

I think it is important to note that the alkyne must be terminal to have a H available for removal.

 

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Mstoothlady2012

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• Jul 26, 2007

• #8

drteeth said:

The triple bond has a high electron density and slightly attracts the H's electrons. This makes the H slightly more acidic then say that of an alkane. The strongly basic Grignard would steel this H. So the CH3(-)MgBr would become CH4...

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thts right!

 

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BiomajorPreDent

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• Jul 20, 2009

• #9

I resurrected this thread because I have a question relating to it.

If you react the grignard with the terminal alkyne and form the alkanide ion, you can then react it with any carbonyl group such as a ketone and it would act as a nucleophile and add like a normal grignard reagent right?

 

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L

loveoforganic

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• Jul 20, 2009

• #10

Well it would react like a grignard, but it wouldn't be a grignard. You'd also obviously have an incompatibility with carboxylic acids.

 

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