To work out the theoretical yield of the preparation of dibenzalacetone, it is useful to first have a reaction equation complete with molar ratios. Using the following equation, what is the correct stoichiometric ratio of acetone:benzaladehyde to yield dibenzalacetone? +\ Acetone Benzaldehyde Dibenzalacetone 2:1 1:2 1:1
The Correct Answer and Explanation is:
Correct Answer:1:2 (Acetone : Benzaldehyde)
Explanation
To calculate the theoretical yield of dibenzalacetone, we must first understand the balanced chemical equation and the stoichiometric ratio between the reactants. The reaction used in the preparation of dibenzalacetone is a classic example of an aldol condensation reaction. In this synthesis, acetone (CH₃COCH₃) reacts with benzaldehyde (C₆H₅CHO) in the presence of a base (commonly NaOH) to produce dibenzalacetone (C₁₇H₁₄O) and water as a by-product.
The balanced reaction is: CH3COCH3+2 C6H5CHO→C17H14O+H2O\text{CH}_3\text{COCH}_3 + 2 \, \text{C}_6\text{H}_5\text{CHO} \rightarrow \text{C}_{17}\text{H}_{14}\text{O} + \text{H}_2\text{O}CH3COCH3+2C6H5CHO→C17H14O+H2O
In this reaction:
1 mole of acetone reacts with 2 moles of benzaldehyde.
This occurs because acetone contains two α-hydrogens, one on each side of the carbonyl group, allowing it to undergo two aldol condensations — one with each molecule of benzaldehyde.
The final product, dibenzalacetone, has two benzylidene groups (–CH=CH–C₆H₅) attached to the central carbonyl carbon of acetone.
This stoichiometric ratio is critical for determining the limiting reagent and calculating the theoretical yield of the product. If benzaldehyde is present in excess, then acetone will be the limiting reagent. Conversely, if the ratio is inverted, benzaldehyde becomes the limiting reagent.
Understanding and using the correct molar ratio — 1 mole of acetone to 2 moles of benzaldehyde (1:2) — ensures that the reaction can proceed completely and form one mole of dibenzalacetone per mole of acetone.
Therefore, the correct stoichiometric ratio for this reaction is:
