The Aldol Condensation Reaction Preparation of Benzalacetophenones Chalcones

The Aldol Condensation Reaction Preparation of Benzalacetophenones (Chalcones) 

Benzaldehyde reacts with a ketone in the presence of base to give a, /3-unsaturated ketones. This reaction is an example of a crossed aldol condensation where the intermediate undergoes dehydration to produce the resonance-stabilized unsaturated ketone. 

Crossed aldol condensations of this type proceed in high yield because benzaldehyde cannot react with itself by an aldol condensation reaction because it has no a-hydrogen. Likewise, ketones do not react easily with themselves in aqueous base. Therefore, the only possibility is for a ketone to react with benzaldehyde. 

In this experiment, procedures are given for preparing benzalacetophenones (chalcones). You should choose one of the substituted benzaldehydes and react it with the ketone, acetophenone. All the products are solids that can be recrystallized easily. 

Benzalacetophenones (chalcones) are prepared by the reaction of a substituted benzaldehyde with acetophenone in aqueous base. Piperonaldehyde, p-anisaldehyde, and 3-nitrobenzaldehyde are used. 

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