[CyanoHyd.rin]

Hi,
   I would like to know about the synthesis of sodium acetylide... could anyone help?

Thanks

Jyot

[Rishi]

Hi,

It is quite a complex process. The reaction takes place at either a very low temperature in presence of ammonia or it happens at a high temperature in presence of solvent. A lower temperature is not feasible and hence you are left with the other option.

At higher temperature the sodium metal tends to form tiny granules which cannot be separated from the product. And this is a part of serious concern. Also generating dry acetylene gas is an issue.

[UnintentionalChaos]

You don't need to use sodium metal for this. The typical base of choice is sodium amide (NaNH2) in liquid ammonia solvent, although sodium diisopropylamide or other strong bases may be used. I believe that ethers are also acceptable solvents.

When the intent is to the alkylate the resultant acetylide ion, di-alkylation is difficult to avoid unless the acetylene is protected on one end. An typical approach is to use something like trimethylsilyl acetylene. After alkylation, the group is deprotected, providing a terminal alkyne.

[CyanoHyd.rin]

Probably this is what I will do! Sodium inxylene, heat to 120, and store fast so it forms fine dust cool it down and then raise temp to 80 and pass acetylene. Acetylele to be sourced from cylinders... Seems fair?

[Markov]

Is this for
a) educational/general practice training, or
b) do you need to use sodium acetylide in a synthesis?

If b, you may want to consider that it is commercially available.

[milo2112]

When the intent is to the alkylate the resultant acetylide ion, di-alkylation is difficult to avoid unless the acetylene is protected on one end. An typical approach is to use something like trimethylsilyl acetylene. After alkylation, the group is deprotected, providing a terminal alkyne.

You can also feed your electrophile into an excess of the NaCCH, this tends to reduce (sometimes drastically) the amount of over reaction.

[Brooks2]

....then raise temp to 80 and pass acetylene. Acetylele to be sourced from cylinders...

For safety, Acetylene gas is dissolved in a solvent (either acetone or DMSO) in cylinders. As you draw down the cylinder, you will begin to get some of the solvent along with the acetylene.