Reduction of a ketone using zinc in acetic acid

In summary, Ozonolysis is a useful reaction that can produce different products depending on the workup.
  • #1
mycotheology
89
0
I'm going to be giving a 1st year student chemistry tutoring so I'm going over some of his past exam papers to make sure I know all the stuff but I'm already at a question I can't do:
http://img571.imageshack.us/img571/5716/26705030.png
So from the formula, I can see that the degree of unsaturation for the compound is 2. Theres at least one C=C bond in there but the oxygen could either be a carbonyl group or an alcohol. Seeing as it reacts with H2SO4, I assume its an alcohol and the reaction it undergoes is an acid catalysed dehydration of the -OH group. This will yield the alkene. Then ozonolysis breaks the alkene into 2 ketones or aldehydes. Its the final part that has me confused. I don't know what this zinc reduction is and how it could convert ketones or aldehydes into a cyclic ketone.
 
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  • #2
See here.
Also, ozonolysis doesn't produce the ketone directly. The trioxolane it produces requires a reductive workup.
 
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  • #3
Thanks. Ozonolysis is an even more useful reaction than I thought, I didn't know you can get different products depending on the workup.
 
  • #4
So, do you have an idea about the structures of A,B and the starting material?
 
  • #5
Yeah, the starting compound is two cyclopentane rings bridged by a sigma bond. There is a hydroxyl group attached to one of the bridge carbons. The acid catalysed dehydration either turns the bridge into a double bond (ozonolysis of this product yields 2 molecules of cyclopentanone) or else turns a neighbouring bond into a double bond (ozonolysis of this one yields a molecule with an aldehyde at one end of the chain, a ketone in the middle and a cyclopentane ring at the other end of the chain). Thats a tricky question for a 1st year exam paper in my opinion. The rest of the questions were fairly straightforward, but that one would have definitely caught me out in first year. I tried explaining this to the guy I was tutoring but he didn't know about acid catalysed dehydrations and was only vaguely familiar with ozonolysis reactions so I just taught him about ozonolysis reactions and moved onto the next question.
 
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  • #6
That's what I thought as well and you're right about that being a tricky question for first semester O-chem.
 

1. What is the purpose of using zinc in acetic acid for reducing a ketone?

The combination of zinc and acetic acid is commonly used as a reducing agent in organic chemistry reactions. The zinc acts as the reducing agent, while the acetic acid serves as the solvent and proton source. This combination allows for the efficient reduction of a ketone into an alcohol.

2. How does the reduction of a ketone using zinc in acetic acid work?

The zinc in acetic acid reduces the ketone by transferring two electrons to the carbonyl group, resulting in the formation of an alcohol. This reaction is known as a nucleophilic addition, where the zinc acts as a nucleophile and attacks the electrophilic carbon of the ketone.

3. What are the advantages of using zinc in acetic acid for the reduction of a ketone?

Using zinc in acetic acid as a reducing agent has several advantages. It is a mild and selective reducing agent, meaning it can reduce ketones without affecting other functional groups in the molecule. Additionally, the reaction is generally fast, and the byproducts (zinc acetate and water) are easily separated from the product.

4. Are there any limitations or drawbacks to using zinc in acetic acid for ketone reduction?

One limitation of using zinc in acetic acid for ketone reduction is that it can only reduce ketones with at least one hydrogen atom on the adjacent carbon. Ketones with bulky or electron-withdrawing substituents may not be effectively reduced. Additionally, the reaction may not work well with highly sterically hindered ketones.

5. What are some common applications of the reduction of a ketone using zinc in acetic acid?

The reduction of ketones using zinc in acetic acid has various applications in organic synthesis. It is commonly used to prepare alcohols, which can then be further functionalized to form more complex molecules. It is also used in the production of pharmaceuticals, flavorings, and fragrances.

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