Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: IoanaD on November 08, 2009, 02:09:17 PM
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When carrying out the aldol condensation between acetophenone and
benzaldehyde, a student decides to heat up the reaction flask to make it go faster.
When she takes a TLC at the end of the reaction, she notices a second spot with
similar polarity to the crossed-aldol product. What could this side-product be?
Illustrate with a mechanism (hint: the aldehyde is not involved in this process).
My thought about this was that the enolate that results from the ketone can react with another ketone, meaning aldol condensation would take place as well as crossed condensation. Some thoughts please? :S
Also, why does a product have to be completely dry before taking melting point? It makes sense in my head but i don't know how to properly explain this.
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(hint: the aldehyde is not involved in this process).
My thought about this was that the enolate that results from the ketone can react with another ketone, meaning aldol condensation would take place as well as crossed condensation. Some thoughts please? :S
Based on the hint you are probably right. Another side reaction I've often seen in Aldol addition reactions with formaldehyde at elevated temperature is a crossed Cannizzaro - benzaldehyde may also do this (assuming your Aldol condensation is base catalysed) - but this is not consistent with the clues you've been given, I just though it was worth mentioning.
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I think aldol condensation was followed by michael addition reaction. you can try this mechanism. May be CH2- of the acetophenone (abstracted by base) attacked the beta carbon on the aldol product.
http://www.cerlabs.com/experiments/0534681417.pdf
plz check out the link. I hope it will be helpful.