Alkyne Hydration Question

[w4nt2baDDS]

The following picture shows the confusion I have about the following alkyne hydration reactions:

These reactions are from Chad's reaction list and I tried to check the road maps in the Ochem Destroyer but couldn't find these.

Can anyone verify if alkyne location is critical to their success?

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[DAT Destroyer]

.2:0.0.0.0.0">.2:0.0.0.0.0.0">Here is what to do..... When hydrating a terminal alkyne, use H2S04, water, and HgS04....although simple acid catalysis is known. The result will be a ketone. This also works for internal alkynes, but they should be symmetrical to avoid an isomeric mixture. If you desire an aldehyde, things are a bit more tricky. Use BH3, peroxide and base if the alkyne is INTERNAL. For terminal alkynes, use a bulky Borane such as Sia2BH. This is used to prevent alcohol formation. The details aren't that important for the DAT, however. The yields of these reactions are often over 90%. Use these suggestions and you will be fine.

Good luck on the DAT

Dr. Jim Romano

 

[w4nt2baDDS]

Thanks orgoman, sounds like H2SO4 and HgSO4 work on both internal and external alkynes.

I didn't know about the BH3/H2O2/-OH reaction to make an internal alkyne turn into an aldehyde, that's helpful.

 

[DAT Destroyer]

Thanks orgoman, sounds like H2SO4 and HgSO4 work on both internal and external alkynes.

I didn't know about the BH3/H2O2/-OH reaction to make an internal alkyne turn into an aldehyde, that's helpful.

Aldehydes will only result if the alkyne is terminal......... As I stated.....use Sia2BH....If BH3 is used,,,,,on an internal alkyne.....a ketone is made.......sorry for any confusion.

 

[w4nt2baDDS]

Okay, I see that. Hydroboration will turn an internal alkyne into a ketone not an aldehyde.

Will hydroboration turn a terminal alkyne into an aldehyde like Sia2BH will?

 

[DAT Destroyer]

Okay, I see that. Hydroboration will turn an internal alkyne into a ketone not an aldehyde.

Will hydroboration turn a terminal alkyne into an aldehyde like Sia2BH will?

Sia2BH is an excellent way to turn a terminal alkyne into an aldehyde !!!!! BH3 will not work very well,,,,,,since alcohols can form !!!!

Dr . Romano