The Claisen-Schmidt reaction is a type of condensation reaction that yields α,β-unsaturated ketones. As the reactants an aromatic aldheyde and ketone is used. The aromatic aldehyde do not possess any α- hydrogens it cannot undergo self-condensation. However, if the ketone and base is present it can easily react to form α,β-unsaturated ketone. The reaction intermediate cannot be isolated due to the lability. The product possesses antoher activated hydrogens and is able to react with one more molecule of aromatic aldehyde. The following experiment demonstrates the formation of mono- and bis- aduct and their diferentiation. Mono- aduct is formed when the large excess of acetone is used. The excess is used in order to minimize the second condensation step. The second experiment involves using ethanol as a solvent to maintain the initial condensation product in the solution and 2:1 molar ratio benzalydehyde:acetone.
Preparation of E-4-phenylbut-3-en-2-one (benzylideneacetone)
To a 100 mL round bottom flask 8.0 mL (8.4 g, 80 mmol) of benzaldehyde followed by 16.0 mL (12.7 g, 220 mmol) of acetone was added. The flask was immersed in warm water bath and under constant stirring 2 mL of 2.5M aqueous sodium hydroxide solution was dropwise added to the mixture. The mixture was stirred for 90 minutes. When the reaction was complete diluted hydrochloric acid was added until the solution was slightly acidic. The mixture was extracted two times with 15 mL of diethylether. It was then washed with 15 mL of water, dried over anhydrous sodium sulfate and the solvent was distilled off using RVE. Yield: 93.7 %.
Preparation of 1,5-diphenyl-(E,E)-1,4-pentadien-3-one (dibenzylideneacetone)
2.5 g of sodium hydroxide was disolved in 25 mL of water. To the solution 15 mL of ethanol was added and the mixture was cooled down in the stream of cold water. The mixture was added to the 100 mL Erlenmayer flask contaning 2.5 mL (2.6 g, 25 mmol) of benzaldehyde and 0.9 mL (0.75 g, 13 mmol) of acetone. The mixture was stirred for 15 minutes. The precipiate formed was filtered off with suction and washed thoroughly with cold water. The product was dried in the air and weighted. Yield: 40.8 %.