Chemistry 351 - Principles of Organic Chemistry II
Spring 2022, Winona State University, Dr. Thomas Nalli

Expt 5. Preparation of a Dibenzalacetone Derivative vial Aldol Condensation

Relevant textbook reading - Klein, Chapter 21

Overview – In this experiment, you will carry out a double crossed aldol condensation reaction. The reaction uses the simple starting materials, acetone and 4-chlorobenzaldehyde, to form the 17-carbon product, 1,5-bis(4-chlorophenyl)penta-1,4-dien-3-one. The common name of the product minus the chlorines is dibenzalacetone so we will refer to it as dichlorodibenzalacetone or DCDBA. The obtained crude  product will be recrystallized and characterized by IR, NMR, and melting point determination.

equation
Procedures

Running the reaction.

  • In a 50-mL Erlenmeyer flask equipped with a magnetic stirring bar, prepare a mixture of 7.5 mL EtOH, 1.5 mL 10% NaOH, and 1.5 mL water.
  • To the stirring solution add 0.0143 mol 4-chlorobenzaldehyde.
  • Add 0.0065 mol acetone and note the time. (You will want to time your observations throughout the reaction.)
  • Continue stirring for 30 min.

Work-up procedures.

  • Add 10 mL water, and then vacuum filter the mixture.
  • Wash the solid three times with 25-mL of water each time.
  • Allow the vacuum to pull air through and press the solid dry by pressing a filter paper or rubber glove to squeeze out more water.
  • Measure the crude yield and save a small sample for melting point determination.
  • Recrystallize the crude product from ethanol.
  • Allow the crystals to dry thoroughly on the vacuum and pressing as before.
  • Measure the final yield.

Characterization of Product

Obtain the 1H and 13C NMR spectrum using CDCl3 as the solvent.

Obtain an IR spectrum using the dry film method.

Obtain the mp of both the crude and final products.


Assigned Questions

1. Why is it important to add the benzaldehyde first and then the acetone rather than in the opposite order?
2. What is the purpose of the water washes in step 2 of the work up procedure?
3. What does the coupling constant observed for the alkene proton doublets reveal about the stereochemistry of the product?