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Topic: ethyne questions  (Read 5550 times)

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Offline maakii

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ethyne questions
« on: February 10, 2007, 09:32:05 PM »
hi, thanks to anyone who helps me answer these questions!

1) I was wondering if ethyne could be double deprotonated to give just 2 carbon atoms with a 2- charge?

2) Secondly, how can ethyne be both hydrogenated and deprotonated by Na/ liquid NH3?

3) If you deprotonate ethyne using Na/ NH3, to give a carbanion, then react it with aldehyde, will it only give a product that only goes though 1 round of addition (added only on 1 side)

or will it react further with 2 equivalents of aldehyde to give a product which has been added on both sides?


Offline english

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Re: ethyne questions
« Reply #1 on: February 10, 2007, 09:38:37 PM »
Once you deprotonate acetylene (ethyne) it becomes acetylide, a very strong base.  Using this understanding, do you think it would want to lose another proton?

Offline movies

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Re: ethyne questions
« Reply #2 on: February 11, 2007, 05:57:28 PM »
It can be done!  Calcium carbide is CaC2.  True though, these dianions are petty rare.

Offline english

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Re: ethyne questions
« Reply #3 on: February 11, 2007, 07:05:21 PM »
It can be done!  Calcium carbide is CaC2.  True though, these dianions are petty rare.

Why did I have a feeling you were going to say that.

 ;D

Offline maakii

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Re: ethyne questions
« Reply #4 on: February 12, 2007, 04:39:32 AM »
ah i see thank you! so if i use a regular base (NaNH2) it would only deprotonate once, yes i got it!

any one knows the answers to the other 2 questions?

Offline movies

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Re: ethyne questions
« Reply #5 on: February 12, 2007, 12:50:09 PM »
For your second question, it's a matter of how you run the reaction.  In one case, you would dissolve the alkyne in NH3 and add Na(0) to the pot.  As the Na dissolves, the alkyne would get reduced to the alkene.

In the other procedure, you first mix Na(0) and NH3, which will eventually react to give NaNH2 (note that this is a much slower pathway than the alkyne reduction described above).  Then, once the NaNH2 has formed, you can add the alkyne and generate the sodium acetylide.

Of course, you can also just buy NaNH2 to begin with, then it's easy!

Offline HP

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Re: ethyne questions
« Reply #6 on: February 12, 2007, 02:10:36 PM »
C2H2 + 2AgNO3--> C2Ag2 (precipitate)
Also with some Cu2+ salts giving Cu carbide...
xpp

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