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The preparation, reaction, and workup process for an aldol condensation experiment. Students are required to study the manual, lecture notes, and textbook to understand the concept of condensation reactions, the role of reactants, solvents, and catalysts, and safety considerations. The experiment involves mixing acetone and benzaldehyde in the presence of sodium hydroxide and ethanol, filtering and washing the product, and recrystallizing it. Quizzes may include predicting products and explaining mechanisms of aldol reactions and condensations.
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Unlike most of the experiments in this course, this experiment is not done on a microscale. It is still a considerably smaller-scale reaction than those that were done in organic chemistry laboratories in the past. Note that there is an error in the equation given for the reaction in Williamson. See if you can find it.
PRE-EXPERIMENT ASSIGNMENT
Study this chapter in the manual, the lecture notes on the Chemistry Department web site, and pages 455-456 in Williamson. You will also find it helpful to study the sections on the aldol reaction and condensation in your lecture textbook. Do the first parts of your notebook writeup.
A student who has prepared for the Aldol Condensation experiment should be able to:
Quizzes given after the experiment has been performed may also include:
The Reaction
Obtain 4 mL of 5 M aqueous sodium hydroxide solution and 4 mL of 95% ethanol. Add them to a 25 mL Erlenmeyer flask and swirl to mix. In a separate flask mix 0.6 mL of acetone (d = 0.79 g/mL) with 1.75 mL of benzaldehyde (d = 1.0 g/mL). Add half of the acetone/benzaldehyde mixture to the sodium hydroxide/ethanol mixture. Swirl the result. The mixture should quickly change from yellow to orange and warm up a bit. A yellow precipitate should begin to appear almost immediately, though the exact colors may vary slightly. As soon as the reaction starts, add the rest of the acetone/benzaldehyde mixture to the flask. Allow the reaction to proceed for about fifteen minutes, swirling occasionally.
The Workup
After fifteen minutes, suction-filter the mixture using your large Büchner funnel and filter flask. Disconnect the vacuum, wash the product with a few milliliters of cold ethanol, and reconnect the vacuum. Allow the suction to run for about five minutes longer to help air dry the crude product. Weigh the crude product and put some in a capillary so you can determine its melting point later.
Recrystallization
Add the remaining crude product to 5 mL of ethyl acetate in a 50 mL beaker. Warm it in a hot water bath ( not directly on a hot plate ) while stirring frequently. Add 5 mL of 95% ethanol, stir, remove from heat, and stir constantly until crystals begin to form. Cool slowly to room temperature and then use an ice-water bath. Collect the crystals by suction filtration. Spread the crystals out on the filter paper as much as possible. To help the crystals dry faster, allow the vacuum to run for at least five minutes after the last of the liquid has been pulled through the funnel. Determine the mass of these crystals and the melting point of both these crystals and the crude product. Calculate the percentage yield.
CLEANUP
Used Pasteur pipettes and melting point capillaries are placed in the broken glass box. Leftover ethanol and ethyl acetate are placed in the non- halogenated liquid waste bottle in the hood; your product goes in the non- halogenated solid waste bottle if your instructor does not collect it. Leftover NaOH solution in small amounts is washed down the drain with plenty of water.