Preparation of Dibenzal Acetone
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Preparation of Dibenzal Acetone - Practical Experiment

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Dibenzalacetone is also known as dibenzylideneacetone and dba. It's an organic compound with the C17H14O formula. It is used as a component in sunscreens and some industrial organometallic compounds as it binds with metals and helps form a stable chemical structure. It is a pale-yellow solid that does not dissolve in water but dissolves in ethanol. It's a non-polar, symmetrical molecule. In this article, we will study how to prepare a pure sample of dibenzalacetone in detail.


Aim

To prepare Dibenzal acetone(organic compound) from benzaldehyde and acetone in the presence of sodium hydroxide.


Theory

Aromatic aldehyde, in the presence of an alkali, undergoes a condensation reaction with an aldehyde or ketone containing alpha hydrogen atoms. This reaction is named as Claisen-Schmidt reaction. In the presence of sodium hydroxide,  aldehydes can condense with another aldehyde or ketone by eliminating a water molecule. Thus, with one mole of acetone, moles of benzaldehyde condense to give Dibenzal acetone. Given below the reaction shows how to prepare dibenzalacetone-

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In the same way, to give cinnamic aldehyde, benzaldehyde condenses with acetaldehyde and one equivalent of acetone to give benzal-acetone.

Other names of dibenzalacetone are Dibenzylideneacetone, 1,5-Diphenylpenta-1,4-dien-3-one, trans,trans-Dibenzylideneacetone.


Materials Required

List of materials required to prepare a sample of dibenzalacetone

  1. Benzaldehyde

  2. Acetone

  3. Sodium hydroxide solution

  4. Methylated spirit

  5. Dilute hydrochloric acid

  6. Ether

  7. Beaker

  8. Funnel

  9. Conical flask

  10. Filter papers


Procedure

There are stepwise method given below to prepare a sample of dibenzalacetone. 

  1. Add 10ml of freshly distilled benzaldehyde and 20ml of acetone to a conical flask. 

  2. Place the flask in a cold bath of water and then, with regular stirring, add 2.5ml sodium hydroxide dropwise. 

  3. Keep the temperature at 30 oC. 

  4. stir the mixture for 2 hours after the complete addition of sodium hydroxide. 

  5. To the reaction mixture, add dilute hydrochloric acid and then transfer to a 250ml separating funnel. 

  6. To the mixture, apply 20ml of chloroform/ether and shake thoroughly. 

  7. Shake the mixture completely, remove the organic layer and repeat the process twice. 

  8. cool the ice-water mixture. As a fine emulsion, Dibenzal acetone separates initially and then forms yellow crystals.

  9. Under pressure, distill the residual portion and collect the fraction that boils at 150c. 

  10. Wash with cold water the pale yellow crystals, dry them and crystallize with ethanol. 


Observation

Colour of the crystals

Pale yellow

Expected Yield

4gm

Melting Point

112 oC


Results and Discussion

The yield of Dibenzal Acetone is ______gm.

The synthesis of a pure sample of dibenzalacetone from excess benzaldehyde and acetone in the presence of NaOH and ethanol has served as a useful example of the Claisen-Schmidt (crossed aldol) condensation reaction, despite the presence of impurities in the recrystallized product. The selection of an aldehyde without alpha hydrogen (benzaldehyde) minimizes the risk of condensation of self-aldol as well as the undesirable synthesis of by-products of self-aldol.


Precautions

  1. Whenever there is a vigorous reaction within the flask, release the pressure by opening the cork of the flask from time to time. 

  2. Do not raise the temperature beyond 30 oC. 

  3. It is important to keep ethanol and acetone away from the flame.


Did You Know?

In this experiment to synthesize dibenzalacetone, the Claisen-Schmidt condensation, a crossed aldol condensation, was used. The Claisen-Schmidt condensation requires a ketone enolate, such as acetone, and an aldehyde that acts as the electrophile, unlike the self-aldol condensation reaction. 

Benzaldehyde, since it contains no alpha hydrogen, is an excellent electrophile; it can not be deprotonated by a base such as sodium hydroxide and thus does not form an enolate (nor will it compete with the acetone enolate). This makes acetone enolate possible to act as a nucleophile and bind (and add) to the aldehyde molecule. In addition, the use of an aldehyde without alpha hydrogens limits the formation of undesirable side products such as monobenzalacetone.


FAQ (Frequently Asked Questions)

1. Why is Dibenzalacetone yellow?

Since dibezalacetone is an aromatic compound and consists of a conjugated pi system that absorbs light in the visible region, so it absorbs by maximum up to 380nm and thus gives off yellow, hence it appears to be yellow in color.

2. Why is Dibenzalacetone used in sunscreens?

A common ingredient in sunscreen is dibenzalacetone. This is because UV light is absorbed by dibenzalacetone and helps shield the skin from the harmful rays of the sun. Another important thing is that the compound does not cause any allergic reaction.

3. What is the Schmidt Claisen Reaction?

It is an organic reaction in which an alpha-hydrogen holding ketone or aldehyde reacts with an aromatic carbonyl compound that has no alpha-hydrogens. This reaction has been named after the chemist J.G. Schmidt and Ludwig Claisent Rainer.

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