Aldol

Only available on StudyMode
  • Download(s) : 183
  • Published : December 9, 2012
Open Document
Text Preview
Aldol Condensation: Synthesis of Dibenzalacetone

Aldol Condensation: Synthesis of Dibenzalacetone

Leah Monroe May 15, 2003

Organic Chemistry Lab II Experiment performed on May 6 and 8, 2003

Abstract:
The purpose of this experiment was to synthesize dibenzalacetone via an aldol condensation reaction between acetone and benzaldehyde. This was done by mixing the two reactants with NaOH and ethanol, then allowing the reaction to sit for thirty minutes. The crystals were then washed with water three times and recrystallized using ethanol. It was then characterized using melting point analysis. The percent yield for this reaction was 59.84%. This was due to loss of crystals during recrystallization and during solvent removal from the reaction mixture. The observed melting point was 104 – 107.5°C, compared to a literature value of 110°C. The lower and broader observed melting point may have been due to the product still being wet. It may also be due to unevaporated ethanol or other impurities in the product. However, the observed melting point was close to the literature value, and it can thus be concluded that the product was dibenzalacetone. Thus, the aldol condensation reaction was successful.

Aldol Condensation: Synthesis of Dibenzalacetone Introduction: The purpose of this experiment is to synthesize dibenzalacetone via an aldol condensation reaction between acetone and benzaldehyde. The product will be recrystallized using ethanol, then characterized using melting point analysis.

Materials Used:
2 beakers, 100-mL 2 vials, 5-mL 10-mL Erlenmeyer flask 25-mL Erlenmeyer flask filter paper rubber bulb support stand sand bath ice (for ice bath) melting point capillary tubes 100 µL micropipet Pasteur pipettes, plastic glass Pasteur pipettes glass stirring rod Hirsch funnel clamp watch glass

Reagents and Properties:
Substances Formula Weight, g/mol Amount Used Moles Used Mole Ratio Melting Point °C Boiling Point °C Density g/mL

Acetone Benzaldehyde Dibenzalacetone ethanol 10 % Sodium Hydroxide

58.08 106.12 224 46.07 40.00

38 µL 100 µL Product 2.8 mL 1.0 mL

5.17 x 10-4 9.84 x 10 N/A 0.048 0.05325
-4

1 to 1 1 to 1 N/A N/A N/A

N/A N/A 110 N/A N/A

56 178 N/A 78.5 N/A

0.731 1.044 N/A 0.791 2.130

Reaction and its Mechanism:
O CH3 C CH3 + 2 Ph Acetone O C H Ph CH CH Benzaldehyde O C CH CH Ph Dibenzalacetone

O CH3 C

Acidic

O
-

O
H2O

OH CH2 CH
-

OH O Ph C H CH2 OCH CH Ph Ph CH CH

O + OH CH3 C
-

O C

CH

CH

Ph

OH
H2O

O CH2 C
-

OH CH CH Ph
-H+

Ph

CH

Ph

CH

OH

-

CH3 C

Ph

-H+

CH3 C

-

CH2 H + OH

CH3 C

CH2

O Ph C + H

O CH3 C

OCH2 CH Ph

O CH

OH CH Ph
OH-

O CH3 C CH CH Ph + H2O

O C CH CH Ph

O CH C CH CH Ph

O
OH-

Ph

CH

CH

C

CH

CH

Ph

Dibenzalacetone

Aldol Condensation: Synthesis of Dibenzalacetone Procedure: Part 1 – Condensing Acetone with Benzaldehyde Prepare an ice-water bath in a 100-mL beaker. Place 0.75 mL ethanol and 1.0 mL 10% NaOH in a 10-mL test tube. Place this tube in the ice-water bath to cool to approximately 20 °C. Remove the tube from the ice bath. Prepare a mixture of 100 µL fresh benzaldehyde and 38 µL acetone. Add this mixture to the ethanol-NaOH solution in two separate portions, approximately 5 minutes apart. Then, let the solution sit for 30 minutes, stirring occasionally. Once the thirty minutes is up, cool the mixture in the ice-water bath. Then, use a glass Pasteur pipet and rubber bulb to remove the solvent from the tube. Add 2 mL distilled water to the tube in order to wash the crystals. Remove the water using the Pasteur pipet. Rinse the crystals two more times with 1 mL portions of distilled water each time. Make sure you remove all the solvent from the crystals.

Part 2 – Recrystallization
Prepare a hot water bath by placing approximately 50 mL of water into a 100-mL beaker. Heat the water to boiling using a sand bath. Add...
tracking img