“Synthesis of dibenzalacetone (DBA)”

 

“Synthesis of dibenzalacetone (DBA)”

Theory:

Dibenzalacetone can be synthesized via a crossed aldol condensation reaction between benzaldehyde and acetone. The reaction involves the nucleophilic addition of the α-carbon of the carbonyl group of acetone to the carbonyl carbon of benzaldehyde, followed by dehydration to form dibenzalacetone.

Materials Required:

• Weigh Balance
• Ice bath
• Beaker
• Stirrer
• Filter paper

Chemicals Required:

1. Benzaldehyde (C₇H₆O) (20 mL)
2. Acetone (C₃H₆O) (10 mL)
3. Sodium hydroxide (NaOH) (catalytic amount)
4. Hydrochloric acid (HCl) (few drops)
5. Water (for washing)

Chemical Equation:

Mechanism:

Procedure:

1. Set up an ice bath by placing a large beaker or bowl filled with ice and water.
2. In a separate reaction flask, add 20 mL of benzaldehyde and 10 mL of acetone.
3. Place the reaction flask in the ice bath to maintain a low temperature.
4. Slowly add a catalytic amount of a base, such as sodium hydroxide (NaOH), to the reaction mixture while stirring continuously.
5. Continue stirring the reaction mixture in the ice bath for about 30 minutes.
6. After the reaction time has elapsed, remove the flask from the ice bath and add a few drops of concentrated hydrochloric acid (HCl) to acidify the mixture.
7. Allow the reaction mixture to settle, and collect the yellow precipitate formed, which is dibenzalacetone.
8. Wash the collected dibenzalacetone with water to remove any impurities, and then dry it. 

Calculations:

To calculate the theoretical yield and percentage yield, we need the actual yield value from the experiment. Let's assume the actual yield of dibenzalacetone obtained is 8.5 grams.

Theoretical Yield:

In the synthesis of dibenzalacetone, the molar ratio between benzaldehyde and dibenzalacetone is 1:1.

To calculate the moles, we can use the formula:

Moles = Mass / Molar mass

Moles of Benzaldehyde= Molar mass of benzaldehyde (C₇H₆O) = 106.12 g/mol

Moles of benzaldehyde = 20 g / 106.12 g/mol

Calculating the above expression gives:

Moles of benzaldehyde = 0.188 moles

Moles of Benzaldehyde: Since the molar ratio between benzaldehyde and dibenzalacetone is 1:1, the moles of benzaldehyde will be the same as the moles of dibenzalacetone.

Moles of dibenzalacetone = 0.188 moles

The molar mass of dibenzalacetone (C₁₇H₁₄O) = 234.29 g/mol

The molar mass of benzaldehyde (C₇H₆O) = 106.12 g/mol

Since the molar ratio is 1:1, the theoretical yield can be calculated as follows:

Theoretical yield = (Actual yield) × (Molar mass of dibenzalacetone) / (Molar mass of benzaldehyde)

Theoretical yield = (8.5 g) × (234.29 g/mol) / (106.12 g/mol)

Calculating the above expression gives:

Theoretical yield = 18.73 g

Percentage Yield:

Percentage yield = (Actual yield / Theoretical yield) × 100

Plugging in the values:

Percentage yield = (8.5 g / 18.73 g) × 100

Calculating the above expression gives:

Percentage yield = 45.4%

Therefore, if the actual yield of dibenzalacetone obtained in the experiment is 8.5 grams, the theoretical yield would be approximately 18.73 grams, and the percentage yield would be approximately 45.4%.