Preparation of Dibenzalacetone: Virtual Lab Synthesis

Dibenzal acetone is also called dibenzylideneacetone. It is an organic compound composed of C, H and O. It is also often abbreviated as dba. It is a pale-yellow solid insoluble in water but soluble in ethanol. It’s a non-polar substance, a symmetrical molecule.

Preparation of dibenzal acetone:

Two equivalents of benzaldehyde react with one equivalent of acetone in the presence of alkali (NaOH) to give β-hydroxy ketone. Further β-hydroxy ketone undergoes a condensation reaction giving rise to α,β-unsaturated ketone. It is an example of a base-catalyzed crossed aldol reaction. It is also called the Claisen-Schmidt reaction.

Mechanism: 

The entire mechanism can be shown basically in four steps. It is completed in the following steps:

Step 1: The acetone reacts with base (NaOH) to get the negatively charged compound for further reaction. This is also called carbanion and acts as an intermediate.

Step 2:  Then carbanion is further reacted with benzaldehyde, followed by hydrolysis to yield beta-hydroxy ketone.

Step 3: The third step involves a condensation reaction to give benzalacetone.

Step 4: Similarly, benzal acetone reacts with a base to generate carbanion as an intermediate. Finally, carbanion reacts with one more equivalent of benzaldehyde, followed by a condensation reaction to give dibenzyl acetone. 

Structure of Dibenzal acetone

The IUPAC name for dibenzyl acetone is 1,5-Diphenylpenta-1,4-dien-3-one. 

The formula for Dibenzal acetone

Dibenzyl acetone is an organic compound with the chemical formula C₁₇H₁₄O.

What is aromatic aldehyde?

The aldehydes in which the aldehydic group (−CHO) is attached with an aromatic structure or group are called aromatic aldehydes.

The simplest aromatic aldehyde is benzaldehyde with the chemical formula C₆H₅CHO. Benzaldehyde is used in the almond extract as a flavouring and as an ingredient in some dye and plastics production.

Examples for aromatic aldehydes:

What is Claisen-Schmidt’s reaction?

Claisen-Schmidt’s reaction was discovered by Rainer Ludwig Claisen and J. G. Schmidt in 1881. Claisen-Schmidt condensation is one of the most widely used methods for carbon-carbon bond-forming reactions, many of which lead to biologically and pharmacologically active compounds. 

The Claisen-Schmidt reaction is a crossed aldol condensation. Aromatic aldehyde lacking an α-hydrogen undergoes a condensation reaction with aldehyde or ketone having α-hydrogen atoms in the presence of an alkali. This reaction is called the Claisen-Schmidt reaction. 

For example, Benzaldehyde lacking an α-hydrogen undergoes a reaction with acetone which contains α-hydrogen in the presence of alkali to give alpha-hydroxy ketone. Further alpha-hydroxy ketone undergoes a condensation reaction giving rise to α,β-Unsaturated ketone.

What is condensation reaction?

In organic chemistry, a condensation reaction is a chemical reaction in which the loss of a small molecule such as water occurs when two molecules are combined to form a single molecule.

Example: In the crossed aldol reaction, the addition of the two molecules typically proceeds stepwise to the additional product, such as alpha hydroxy ketone. Further, it will undergo loss of water molecules to produce condensation products usually, these are in equilibrium.

Applications of Dibenzalacetone

• Dibenzalacetone is used in the manufacturing of sunscreens. This is because dibenzalacetone absorbs UV light and helps to protect the skin from the sun’s damaging rays.
• It acts as a ligand in preparing organometallic complexes, and these complexes will be used as catalysts in the coupling reactions.
• Many important derivatives of dibenzalacetone are prepared from the compound for their antioxidant properties.

Preparation of Dibenzalacetone Experiment

Experiment Title – Preparation of Dibenzalacetone

Experiment Description – Benzaldehyde undergoes condensation with acetone in the presence of aqueous sodium hydroxide (NaOH) to give dibenzalacetone. Let’s prepare this organic compound in a virtual lab.

Aim of Experiment – To prepare dibenzalacetone (dibenzylideneacetone)

Apparatus and Material Required – 

Apparatus

• Conical flask
• Beaker  
• Buchner funnel 
• Ice bath         

Chemicals

Acetone: 2.3 mL
Distilled water
Ethanol: 25 mL
NaOH : 3.15 g
Benzaldehyde: 3.2 mL

Procedure – 

• First, a solution of 3.15 g sodium hydroxide mixed with 25 mL ethanol and 30 mL distilled water should be prepared in a beaker. 
• Cool the beaker in an ice bath maintained at a temperature of about 20–25 °C. 
• We will prepare a mixture of 3.2 mL of benzaldehyde and 2.3 mL of acetone in a conical flask. 
• We will slowly add half of this mixture to the ice-cooled NaOH solution prepared in step (i) with vigorous stirring. 
• A fluffy precipitate will form within a few minutes. 
• Stir the mixture gently for about fifteen minutes. Then, we will add the remaining mixture of benzaldehyde and acetone and stir for 30 more minutes. 
• Filter the pale yellow solid obtained and wash with cold water. 
• Dry it and recrystallise its small amount of ethanol.

Precautions – 

(a) Maintain the temperature at around 20 °C while shaking the reaction mixture. 

(b) Always use freshly distilled benzaldehyde or the sample from a freshly opened bottle.

FAQs on Preparation of Dibenzalacetone