Dibenzal Acetone Preparation
Practicals form an important part in the lesson of Chemistry. Hands-on experience not only develops the practical skills of the students but also an understanding of the importance of scientific concepts and methods. The practical classes also prepare the students to understand and deal with safety hazards in chemistry laboratories and learn how to work safely.
Preparation of Dibenzal acetone falls in the Organic Chemistry practical syllabus.
Preparation of Dibenzal Acetone - Practical Experiment
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
The preparation of dibenzalacetone from benzaldehyde and acetone proceeds by the procedure of Claisen-Schmidt reaction which is a condensation reaction between aromatic aldehydes or aldehyde with ketone in the presence of an alkali.
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
Benzaldehyde
Acetone
Sodium hydroxide solution
Methylated spirit
Dilute hydrochloric acid
Ether
Beaker
Funnel
Conical flask
Filter papers
Procedure
There are stepwise method given below to prepare a sample of dibenzalacetone.
Add 10ml of freshly distilled benzaldehyde and 20ml of acetone to a conical flask.
Place the flask in a cold bath of water and then, with regular stirring, add 2.5ml sodium hydroxide dropwise.
Keep the temperature at 30 oC.
stir the mixture for 2 hours after the complete addition of sodium hydroxide.
To the reaction mixture, add dilute hydrochloric acid and then transfer to a 250ml separating funnel.
To the mixture, apply 20ml of chloroform/ether and shake thoroughly.
Shake the mixture completely, remove the organic layer and repeat the process twice.
cool the ice-water mixture. As a fine emulsion, Dibenzal acetone separates initially and then forms yellow crystals.
Under pressure, distill the residual portion and collect the fraction that boils at 150c.
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
Whenever there is a vigorous reaction within the flask, release the pressure by opening the cork of the flask from time to time.
Do not raise the temperature beyond 30 oC.
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.
Conclusion
The practical experiment for the preparation of Dibenzal Acetone describes the detailed process of preparing Dibenzal Acetone from benzaldehyde and acetone in the presence of sodium hydroxide. The process covers the aim of the experiment, the theory behind it, materials required, step-by-step procedure, observation, results, and discussion.
FAQs on Preparation of Dibenzal Acetone
1. What is the basic chemical structure of dibenzalacetone?
Dibenzalacetone (chemical formula C₁₇H₁₄O) is an unsaturated ketone. Its structure is formed when one molecule of acetone condenses with two molecules of benzaldehyde. This creates a chain with a central ketone group flanked by two phenyl groups and double bonds, resulting in an extended conjugated system.
2. How is dibenzalacetone prepared in a laboratory?
Dibenzalacetone is typically prepared through a reaction known as the Claisen-Schmidt condensation. In this process, two equivalents of benzaldehyde (an aldehyde with no alpha-hydrogens) react with one equivalent of acetone in the presence of a base, such as sodium hydroxide (NaOH), and ethanol as a solvent. The reaction involves the formation and subsequent dehydration of an aldol adduct to yield the final product.
3. What is a Claisen-Schmidt condensation reaction?
The Claisen-Schmidt condensation is a specific type of crossed aldol condensation. It occurs between an aldehyde or ketone that has alpha-hydrogens and a carbonyl compound that lacks them. The compound without alpha-hydrogens (like benzaldehyde) can only act as an electrophile, preventing self-condensation and leading to a more controlled reaction with a single major product.
4. What are the main applications of dibenzalacetone?
Dibenzalacetone is valued for its unique properties and is used in several fields:
- Sunscreens: It is highly effective at absorbing UV light, protecting the skin from sun damage.
- Organometallic Chemistry: It is used as a stable ligand to create catalysts, such as tris(dibenzylideneacetone)dipalladium(0), which are important in organic synthesis.
- Material Science: It serves as a component in creating certain polymers and advanced materials.
5. Why does dibenzalacetone have a distinct yellow colour?
The yellow colour of dibenzalacetone is due to its extended conjugated system of alternating single and double bonds, which includes the benzene rings and the carbon-carbon double bonds. This system absorbs light in the high-energy blue-violet region of the visible spectrum. As a result, it reflects the complementary colour, which is yellow, making the compound appear yellow to our eyes.
6. What is the specific role of sodium hydroxide (NaOH) in this preparation?
Sodium hydroxide acts as a base catalyst in the Claisen-Schmidt condensation. Its primary role is to remove an acidic alpha-hydrogen from the acetone molecule. This creates a highly reactive nucleophile called an enolate ion, which then attacks the carbonyl carbon of a benzaldehyde molecule, initiating the condensation process.
7. What makes dibenzalacetone such an effective ingredient in sunscreens?
Dibenzalacetone is effective in sunscreens because its conjugated pi-electron system is excellent at absorbing harmful ultraviolet (UV) radiation, particularly UV-B rays. When it absorbs this energy, the molecule gets excited to a higher energy state and then releases the energy harmlessly as heat, preventing the UV rays from penetrating the skin and causing cellular damage. It is also stable and generally non-allergenic.
8. Why is it important that benzaldehyde has no alpha-hydrogens for this reaction?
It is crucial that benzaldehyde lacks alpha-hydrogens to prevent self-condensation. If the aldehyde had alpha-hydrogens, the base (NaOH) could deprotonate it, leading to a mixture of unwanted side products. By using benzaldehyde, we ensure that only acetone can form the enolate nucleophile, forcing it to react with the benzaldehyde electrophile and yielding dibenzalacetone as the primary, desired product.
