Experiment 11: Synthesis of Dibenzalacetone by the Aldol condensation Introduction:
The Aldol condensation reaction, under basic conditions, involves the nucleophilic addition of an enolate ion to another carbonyl group. The resulting product, a beta-hydroxy ketone or aldehyde, is called an aldol because it contains both and aldehyde group and the hydroxy group of alcohol. Condensations, including aldol condensation, combine two or more molecules, typically with a loss of a smaller molecule (including water or alcohol). In the presence of a base, the aldol condensation occurs by a nucleophilic addition of the enolate ion (a strong nucleophile) to a carbonyl group. The final step, protonation, gives the desired aldol. In this lab, the Aldol condensation reaction took place in basic conditions, with NaOH and EtOH, however, this reaction can also take place in acidic conditions as well. The enol can serve as a weak nucleophile to attack a protonated carbonyl group.
The first is an example of self-condensation. In this lab, we were performing a mixed condensation, so this side reaction would not be favorable. The second reaction would occur if there was excess acetone in the reaction, causing acetone to further react with the desired final product. The last side reaction is due to not enough acetone in the reaction, only able to add to one side of the carbonyl and ultimately in the wrong position. This is why it was important to pay special attention to the amounts of reactants added to the mixture.
In a medium sized test tube
* Add 4 mL of 3M NaOH solution
* Add 3 mL of 95% ethanol
* Add .424 g of benzaldehyde
* Add .116 g of acetone
Take a TLC of mixture
Cap tube with cork and shake mixture vigorously for 30 minutes * Add 3 mL of water into test tube and cap the tube and shake vigorously Repeat 3 times
Remove the liquid from test tube using Hirsch funnel vacuum filtration Dry and...
References: Wade, L.G. (2006). Organic Chemistry. Upper Saddle River, NJ: Prentice Hall
Weldegirma, S. Experimental Organic Chemistry Laboratory Manual. Department of Chemistry;
University of South Florida, Fall 2011/spring 2012. Pg 93-95.
http://riodb01.ibase.aist.go.jp/sdbs/cgi-bin/direct_frame_top.cgi (literature IR for dibezalacetone)
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