To Prepare a Sample of Dibenzalacetone

Dibenzalacetone is a crystalline solid frequently used as a ligand in the preparation of organometallic complexes that are then used as catalysts in coupling reactions. It is also a common ingredient in some sunscreens because it absorbs harmful UV light.

Table of Contents

• Aim of the Experiment

• Apparatus Required

• Theory

• Procedure

• Observations

• Result

• Precautions

Aim of the Experiment

To prepare a sample of dibenzalacetone.

Apparatus Required

• Benzaldehyde

• Acetone

• Sodium Hydroxide Solution

• Methylated Spirit

• Dilute Hydrochloric Acid

• Ether

• Beaker

• Funnel

• Conical Flask

• Filter Papers

Theory

In the presence of an alkali, aromatic aldehyde condenses with aldehyde or ketone containing alpha hydrogen atoms. This is known as the Claisen-Schmidt reaction. According to Claisen, in the presence of sodium hydroxide, aldehydes can condense with another aldehyde or ketone, thereby removing a water molecule. Dibenzal acetone is formed when moles of benzaldehyde condense with one mole of acetone.

Procedure

• Obtain a conical flask. 10ml freshly distilled benzaldehyde and 20ml acetone are added.

• Place the flask in a cold water bath and gradually add 2.5ml sodium hydroxide while stirring constantly.

• Keep the temperature set at $${{30}^{o}{C}}$$.

• Stir the mixture for 2 hours after adding all the sodium hydroxide.

• Transfer the reaction mixture to a 250ml separating funnel after adding dilute hydrochloric acid.

• Shake the mixture thoroughly after adding 20 ml of chloroform/ether.

• Shake the mixture thoroughly, remove the organic layer, and repeat twice.

• In ice water, cool the mixture. Dibenzyl acetone separates as a fine emulsion first, then as yellow crystals.

• Under pressure, distil the residual portion and collect the fraction boiling at $${{150}^{o}{C}}$$.

• The pale yellow crystals should be washed with cold water, dried, and crystallised with ethanol.

Observations

Result

The yield of DibenzalAcetone is in gm.

Precautions

• When a vigorous reaction occurs inside the flask, periodically release the pressure by opening the flask's cork.

• The temperature should not be raised above $${{30}^{o}{C}}$$.

• Keep ethanol and acetone away from the flame.

Lab Manual Questions

1. Which solvent was used for the recrystallization of dibenzalacetone?

Ans. The dry product from the previous lab period will be recrystallised by using about 20 mL of hot, boiling 95% ethanol. After dissolving, crystals should reform as soon as the solution cools to room temperature (without ice).

2. Which functional group is present in dibenzalacetone?

Ans. Dibenzalacetone contains a ketone and two alkene functional groups.

3. Is it necessary to recrystallise the dibenzalacetone?

Ans. Yes, it is important to recrystallise a compound obtained from a reaction.

4. Is dibenzalacetone soluble in water?

Ans. Dibenzalacetone is insoluble in water.

Viva Questions

1. What kind of isomerism is involved in the synthesis of dibenzalacetone?

Ans. This dibenzalacetone can show cis-trans geometrical isomerism due to a double bond.

2. What is the density of dibenzalacetone?

Ans. The density of dibenzalacetone is 1.1±0.1 g/$${{cm}^{3}}$$.

3. What side products are formed in the aldol condensation of dibenzalacetone?

Ans. $$\beta$$-hydroxy aldehyde is the product of the aldol condensation of dibenzalacetone.

4. Why is ethanol used in the recrystallization of dibenzalacetone?

Ans. Sufficient alcohol is used to dissolve the benzaldehyde rapidly and to retain the benzalacetone in the solution until it has had time to react with the second aldehyde molecule. 

5. What is the intermediate formed in the synthesis of dibenzalacetone?

Ans. Benzaldehyde is the intermediate product in the synthesis of benzalacetone.

6. Is dibenzalacetone soluble in acetone?

Ans. Yes. Benzalacetone is soluble in acetone.

7. What is the limiting reagent in aldol condensation?

Ans. Acetone is the limiting reagent because it produces the least dibenzalacetone.

8. Why can benzaldehyde and acetone undergo double aldol condensation?

Ans. Acetone has $$\alpha$$-hydrogens (on both sides) and thus can be deprotonated to give a nucleophilic enolate anion. As aldol condensation is a type of nucleophilic reaction.

9. What is the molar ratio of benzaldehyde and acetone required to make dibenzalacetone?

Ans. To prepare dibenzalacetone 2:1 molar ratio of benzaldehyde and acetone is required.

10. What is the purpose of dibenzalacetone by the aldol condensation?

Ans. Aldol condensation is an important route of organic synthesis because it provides an efficient way to form carbon-carbon bonds. In this condensation, an enol or enolate ion reacts with a carbonyl compound to form a β-hydroxy ketone or β-hydroxyaldehyde, followed by dehydration. As dibenzalacetone is an organic compound, it is required to undergo aldol condensation.

Practical Based Questions

1.IUPAC name of dibenzal acetone is

(a)1,5-Diphenylpenta-1,4-dien-3-one

(b)2,5-Diphenylpenta-1,4-dien-3-one

(c)1,5-Diphenylpenta-2,4-dien-3-one

(d)1,5-Diphenylpenta-1,3-dien-3-one

Answer: (a)

2.What is the odour of dibenzalacetone

(a)Sweet almond odour

(b)Bitter almond odour

(c)Sweet odour

(d)Bad odour

Answer: (b)

3. Boiling point of dibenzalacetone is

(a)150 degree celsius

(b)125 degree celsius

(c)130 degree celsius

(d)145 degree celsius

Answer: (c)

4. Melting point of dibenzalacetone is

(a)100 degree celsius

(b)110 degree celsius

(c)111 degree celsius

(d)99 degree celsius

Answer: (c)

5. Benzalacetone is

(a)Acidic

(b)Basic

(c)Neutral

(d)None of the above

Answer: (c)

6. Which of the following is the simplest member of organic compounds?

(a) Formic acid

(b) Formaldehyde

(c) Methane

(d) Methanol

Answer: (c)

7.Synthesis of dibenzalacetone from benzaldehyde known as

(a)Claisen-Schmidt reaction

(b)Swarts reaction

(c)Cannizzaro Reaction

(d)Hoffmann Bromamide Reaction

Answer: (a)

8. Which of the following bonds is made up of many organic compounds?

(a) Metallic bond

(b) Dipolar bond

(c) Ionic bond

(d) Covalent bond

Answer: (d)

9.Which of the following is a classification of Organic compounds?

(a) alicyclic compounds and acyclic compounds

(b) Cyclic compounds and alicyclic compounds

(c) Open chain compounds and acyclic compounds

(d) Open chain compounds and linear chain compounds

Answer: (a)

10. Which of the following is not a class of organic compounds?

(a) Amides

(b) Electro compounds

(c) Nitro compound

(d) Carbonyl compound

Answer: (b)

Conclusion

Dibenzylideneacetone, also known as dibenzalacetone, is an organic compound with the formula $${{C}_{17}{H}_{14}{O}}$$. 

It is a pale yellow solid that is soluble in ethanol but insoluble in water.

Dibenzalacetone is a crystalline solid frequently used as a ligand to prepare organometallic complexes that are then used as catalysts in coupling reactions.

It is also a common ingredient in some sunscreens because it absorbs harmful UV light.