Question

1. Suggest a way to modify the laboratory procedure (offered below) so that the reaction produces monobenzalacetone instead of dibenzalacetone.

Up next i offer the procedure that we went through in the lab:

Lab Title: Dibenzalacetone synthesis

Objective: Conduct a mixed aldol condensation reaction using acetone and benzaldehyde.

Procedure:

1. In a test tube place 50 mL of NaOH at 10% w/v, 40 mL of 95% ethanol, 5.4 g of benzaldehyde and 1.5 g of acetone.
2. Close the tube with a septa and shake vigorously.
3. Continue shaking for 30 minutes.
4. Filter under vacuum with a Buchner funnel. 
5. Wash with water until the filtered liquid is free of the base. This will be verified with pink litmus paper (changes from pink to blue in basic medium).
6. Dry the product in the oven for 5 minutes, let cool.
7. Weight the dibenzalacetone, determine your melting point and calculate the% of performance.

Answer 1

In the preparation of dibenzalacetone, we take banzaldehyde in excess and acetone is our limiting reagent. Now, to get monobenzalacetone, we need to take acetone in excess and benzaldehyde as limiting reagent.

Procedure:

1. In a test tube A place 20 mL of NaOH at 10% w/v, 20 mL of 95% ethanol, 1 g of benzaldehyde. In another test tube B, take 40 mL of NaOH at 10% w/v, 20 mL of 95% ethanol, 10 g of acetone.
2. Now, add slowly (10 drops per 30 s) the content of test tube A in test tube B. 
3. Close the tube with a septa and shake vigorously after every addition.
4. Continue shaking for 30 minutes.
5. Filter under vacuum with a Buchner funnel. 
6. If, precipitate don't formed at room temperature, the place the content in ice for 10-15 min.
6. Wash the ppt with water until the filtered liquid is free of the base. This will be verified with pink litmus paper (changes from pink to blue in basic medium).
6. Dry the product in the oven for 5 minutes, let cool.
7. Weight the monobenzalacetone, determine your melting point and calculate the% of performance