[Ingeniosuccinimide]

Hello,

could anyone help me with two problems in the attachment:

1) what is the theoretical explanation for the fact that in the case of "keto-enol" tautomerism in this pyridine derivative, the equilibrium in practice is largely shifted to the "keto" form?

2) what could happen if this acetylide comes in contact with water, either in trace amounts or huge amount of water?

This problem is actually not an exercise question but an issue in the lab, since I'm doing one reaction with phenylacetylene and NaH, and the reaction mixture is quenched with water to get rid of unreacted NaH. The point of NaH was not to form acetylide but to deprotonate something more acidic, but it seems that phenylacetylene with its pKa≈28 reacts to some extent. What could happen in the scheme drawn here?

Also, why some transition metal acetylides like the copper and silver ones are not only water stable, but actually are prepared in water solutions?

[discodermolide]

Read this for the pyridone: http://en.wikipedia.org/wiki/2-Pyridone

Sodium acetylide and water will form, well what do you think?

[Ingeniosuccinimide]

Read this for the pyridone: http://en.wikipedia.org/wiki/2-Pyridone

Sodium acetylide and water will form, well what do you think?

Thanks for the link.

I'm not sure about the second one, maybe ethynol? I don't believe it's acetylene, since I think of sodium acetylide as Na-C---CH and not Na₂C₂?

As in the reaction that worries me and that I described I don't get phenylacetylene back when it reacts with NaH and carbanion (I presume sodium phenylacetylide is formed). The question is what happens with sodium phenylacetylide in contact with water...

[discodermolide]

Sorry I should have said "The sodium acetylide".

Quenching with water should give you the phenyl acetylene back again and NaOH.

[orgopete]

This problem is actually not an exercise question but an issue in the lab, since I'm doing one reaction with phenylacetylene and NaH, and the reaction mixture is quenched with water to get rid of unreacted NaH. The point of NaH was not to form acetylide but to deprotonate something more acidic, but it seems that phenylacetylene with its pKa≈28 reacts to some extent. What could happen in the scheme drawn here?

Also, why some transition metal acetylides like the copper and silver ones are not only water stable, but actually are prepared in water solutions?

I am not familiar with the procedure you are using, but when I did a copper acetylide coupling, this is how I reasoned the reaction. At first I was surprised that I could form the copper-acetylide in water. Then I began to think about it. In my case, I don't think I formed the copper-acetylide from the anion. I think copper formed a complex with the acetylene, and I deprotonated this to form the copper acetylide. The copper complexing with the acetylene can reduce the pKa of the acetylene so it can be deprotonated in water.

If we search for other reactions in which we might question the equilibria, elimination reactions come to mind. How could sodium ethoxide remove an alkyl proton? The pKa of an alkane is much too great for this to happen. However, if the C-Br bond were to lengthen, then the C-H electrons may be attracted to the back-side of the C-Br bond. I reason that this process will make the proton more acidic. I believe this will be consistent with an anti-periplanar stereochemistry, an E2 mechanism, and a Zaitsev product. At least, this is how I interpret this reaction occurring.