Aldol Condensation (Dibenzalacetone)

Synthesizing a UV-absorbing compound used in sunscreens

Organic Synthesis Advanced (University) 75 min ~$18.00

Objective

Synthesize dibenzalacetone via a crossed aldol condensation between benzaldehyde and acetone, demonstrating carbon-carbon bond formation.

Background

The aldol condensation is one of the most important carbon-carbon bond-forming reactions in organic chemistry. Dibenzalacetone is formed by the double aldol condensation of benzaldehyde with acetone under basic conditions. The bright yellow product absorbs UV light and was once used in sunscreen formulations.

Safety Warnings

  • NaOH is corrosive
  • Benzaldehyde is an irritant with a strong almond odor
  • Acetone is flammable
  • Work in a fume hood

Required PPE

goggles gloves lab_coat

Materials

  • Benzaldehyde (5 mL)
    Fresh, not oxidized
  • Acetone (1.5 mL)
  • Sodium hydroxide (NaOH) (25 mL)
    10% solution
  • Ethanol (20 mL)
    95%
  • Distilled water (100 mL)
    Ice-cold

Equipment

250 mL Erlenmeyer flask Buchner funnel Filter flask Vacuum pump Melting point apparatus Ice bath Magnetic stirrer

Procedure

1

Dissolve 5 mL benzaldehyde in 20 mL ethanol in the Erlenmeyer flask.

3 min Fume hood — benzaldehyde is an irritant
2

Add 1.5 mL acetone to the flask and stir.

2 min
3

Slowly add 25 mL of 10% NaOH while stirring. A yellow precipitate should begin forming.

5 min NaOH is corrosive
4

Stir the mixture at room temperature for 30 minutes.

30 min
5

Cool the flask in an ice bath for 10 minutes to maximize crystallization.

10 min
6

Collect the yellow crystals by vacuum filtration. Wash with cold water.

10 min
7

Dry the product and determine the melting point (pure dibenzalacetone: 110-112°C).

10 min
8

Calculate the percent yield.

5 min

Expected Results

Bright yellow crystals with a melting point of 109-112°C. Typical yield is 60-80%. The product absorbs UV light strongly, which can be confirmed if a UV lamp is available.

Cleanup

Dispose of organic waste in designated containers. Neutralize NaOH waste. Rinse all glassware.

Details

Category
Organic Synthesis
Difficulty
Advanced (University)
Duration
75 min
Est. Cost
$18.00
Steps
8
Materials
5

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Frequently Asked Questions

What is the objective of Aldol Condensation (Dibenzalacetone)?
Synthesize dibenzalacetone via a crossed aldol condensation between benzaldehyde and acetone, demonstrating carbon-carbon bond formation.
How difficult is Aldol Condensation (Dibenzalacetone)?
This experiment is rated as Advanced (University). It takes approximately 75 minutes to complete.
What safety precautions are needed for Aldol Condensation (Dibenzalacetone)?
Key safety precautions include: NaOH is corrosive; Benzaldehyde is an irritant with a strong almond odor; Acetone is flammable.
What materials are needed for Aldol Condensation (Dibenzalacetone)?
The main materials required are: Benzaldehyde, Acetone, Sodium hydroxide (NaOH), Ethanol, Distilled water.
What results should I expect from Aldol Condensation (Dibenzalacetone)?
Bright yellow crystals with a melting point of 109-112°C. Typical yield is 60-80%. The product absorbs UV light strongly, which can be confirmed if a UV lamp is available.