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Author Topic: Aldol condensation between acetophenone and benzaldehyde  (Read 11745 times)

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IoanaD

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Aldol condensation between acetophenone and benzaldehyde
« on: November 08, 2009, 08:09:17 AM »

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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Dan

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Re: Aldol condensation between acetophenone and benzaldehyde
« Reply #1 on: November 09, 2009, 12:36:24 AM »

(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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Med90

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Re: Aldol condensation between acetophenone and benzaldehyde
« Reply #2 on: November 09, 2009, 12:52:03 AM »

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.
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