[Speed, T.J..; McIntyre, J.P.; Thamattoor, D.M. J. Chem. Educ. 2004, 81, 1355-6]
Introduction: You will synthesize a Wittig reagent, react it with an aldehyde to make a good Michael acceptor, and then react the Michael acceptor with a suitable Michael donor in a Michael reaction.
Experimental
Triphenylcarbethoxymethylphosphonium bromide: Dissolve 3.14 g of triphenylphosphine in 6 mL of toluene in a 25-mL Erlenmeyer flask. Add a stir bar and attach a reflux condenser (you probably will not need to run water through it). Prepare a solution of 2.00 g of ethyl bromoacetate in 6 mL of toluene and add it dropwise to the triphenylphosphine solution through the top of the condenser. The mixture will warm up and a solid will precipitate. Stir the mixture for 45 min and then filter the solid. Wash the solid with hexane. Use a clean filter flask and save the filtrate since more salt may precipitate overnight. Characterize the bromide salt.
Triphenylcarbethoxymethylphosphorane (Wittig Reagent): Dissolve the triphenylcarbethoxymethylphosphonium bromide in a minimum amount of water in a round bottom flask (should take about 10 mL per gram). Add an equal amount of toluene as the water. Also put 1-2 drops of phenolphthalein solution into the flask. Add enough 2.5 M NaOH to bring the mixture to the endpoint. Separate the two layers, dry the toluene layer, and evaporate off most of the toluene on a rotary evaporator. Carefully add petroleum ether to cause the phosphorane to precipitate. Dry the solid and characterize it.
Synthesis of Ethyl trans-Cinnamate: Weigh 0.50 g of recently distilled benzaldehyde into a 50-mL round bottom flask equipped with a stir bar. Add 20 mL of dichloromethane and stir for 10 min in an ice bath. Slowly add 2.0 g of the phosphorane. After the addition, stir for another 10 min and then warm the solution to room temperature. Remove the stir bar and evaporate the dichloromethane on a rotary evaporator. Add 20 mL of hexane to the residue in the flask and break up the suspension with a glass rod. Filter the mixture into a clean flask and use another 20 mL of hexane to rinse the round bottom flask. Transfer the filtrate into a clean round bottom flask and evaporate off the solvent using a rotary evaporator. Characterize the final product.
Michael Reaction with Aniline: A mixture of aniline (5 mmol), ethyl trans-cinnamate (4.5 mmol), and glacial acetic acid (5 mL) is heated under reflux for 30 min. Isolate the solid product using vacuum filtration, wash it with ethanol, and dry it. Recrystallize your sample and characterize it.