Destroyer 2013, ochem #169

[tandem7]

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This problem is a Claisen reaction for an ester. It adds a strong base which deprotonates the ester at the alpha position. However, the question also adds acid, which should hydrolyze the ester portion of the final product into a carboxylic acid. Therefore, I would think the answer would be "e" (none of these) but it says it is c, which is an ester product (but I am 100% certain it should be a carboxylic acid after adding the acid). Any thoughts?

 

[Meat Gyver]

I don't have the new DAT destroyer, so I don't know how the question was drawn out but at the end of a Claisen Condensation reaction, you usually add dil.H3O+ (keyword being: dilute) to ensure the alpha (acidic) hydrogen doesn't get deprotonated, since you're still in basic conditions (and that H is very reactive). The fact that it is dilute ensures that the ester doesn't react to become a carboxylic acid. Hope that helped.

 

[J777]

The resulting beta keto ester has particularly acidic hydrogens between the two carbonyl groups, one of which gets easily deprotonated under the basic conditions of the reaction. This forms a resonance stabilized enolate (and is actually the driving force of the reaction). The acid is added in order to reprotonate the carbon.

Just remember that Claisen Condensations require the acid, but since the product is a beta keto ester, it will not form a carboxylic acid like a normal ester would.