[Lo.Lee.Ta.]

I'm trying to convert 4-octyne to butanal...
This the solution for the reaction that takes place:

http://i1261.photobucket.com/albums/ii596/lolita56381/aldehyderxn.jpg

I know that first we have to add H2 and a Lindlar catalyst in order to produce what is the reactant.
I thought adding O3 would be an ozonolysis reaction.
An ozonolysis reaction should yield this:

http://i1261.photobucket.com/albums/ii596/lolita56381/ozonolysisreaction.png

I don't know why they added the Zn and CH3CO2H, though.
 
What does this even do in the reaction? Why couldn't we just add O3 and be done with it?

Thanks!

[discodermolide]

Adding ozone to an alkene gives an intermediate which needs to be treated to give the final compound.
So what is the Zn/acetic doing?

[AlphaScent]

There are 3 things that happen during Ozonolysis.

What are they and why are they happening?


Zinc/Acetic acid is fine, but I have always preferred dimethyl sulfide..both accomplish the same "thing"

[AlphaScent]

Also a bigger fan of P-2 Nickel for Z-olefin formation....

[discodermolide]

The effectiveness of a catalyst really depends upon it's source. I have never had any trouble with the classical Pd/BaSO₄ cat.
But for other reactions we had to scene lots of cats. to get an optimal one.

[Lo.Lee.Ta.]

Oh, okay. So there is an intermediate here.

It looks like the O3 adds to the overall molecule, and the Zn/acetic acid is used to separate that molecule into 2 carbonyls.
http://www.chem.ucalgary.ca/courses/351/Carey5th/Ch06/ch6-10.html

Thanks!

[discodermolide]

The Zn/acetic acid reduces the intermediate ozonide to give the final molecules.

[orgopete]

The Zn/acetic acid reduces the intermediate ozonide to give the final molecules.

Since this is the second question about ozonides, let me illustrate this further. An ozonide could be thought of as a cyclic peroxy acetal. Hydrolysis would give the two aldehydes and hydrogen peroxide. Hydrogen peroxide will react with an aldehyde to produce a carboxylic acid, formally. The reaction can also produce the carboxylic acid directly from the ozonide by loss of a proton and cleavage of the O-O bond. Zinc or dimethylsulfide are two common reagents used to reduce the peroxy-group or hydrogen peoxide and avoid the over oxidation.