[Archer]

Hi All,

I am intending on making propargylic alcohols from substituted benzaldehydes



I was wondering whether anyone knows if there is any particular advantage to using sodium acetylide rather than the corresponding Grignard reagent.

Any tips / guidance would be greatly appreciated.

Kind regards

Archer

[discodermolide]

I think the sodium acetylide may be better than the magnesium because the latter may well trend to self couple and oligomerise.

[rucik5]

I'd probably get ethynylmagnesium bromide (or chloride?) myself - we've had a bottle in the fridge for more than half a year and it was OK (benzaldehyde titration). Also, it's supplied in THF and it's relatively cheap. Sodium acetylide comes in xylenes I think, only. May be a bit of a pain to remove.
Lithium acetylide is another option; I'm not sure about advantages or disadvantages. I believe that Lithio compounds react on average 100 times faster than Grignards (which still react fast and perfectly fine).
Peter

[KrCo]

Some aspects (maybe helpful):

If you want to do it on big scale, the sodium acetylide is ~5 times cheaper.
If you are doing some ‘green chemistry’, the atomic economy is better with the sodium acetylide.
The sodium acetylide is less flammable than the other although both of them may be handled with care.

[clarkstill]

I agree with KrCo; Prof Rubin at UCLA singles out ethynylmagnesium bromide as a pyrophoric liquid:

http://yvesrubin.files.wordpress.com/2011/02/1-pyrophoric-reagents.pdf

while there's no mention of the corresponding lithium acetylide.

And incidentally, that document is extremely useful when instructing people in handling pyrophoric liquids; definitely worth a read.