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. 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.
4. What are the uses of Dibenzalacetone?
It is used as a ligand in the preparation of organometallic compounds because of its binding property with metals to form a stable compound. It is also used in sunscreens to protect the skin from UV rays especially because it is not allergic to skin. It itself absorbs the UV rays and prevents the harmful rays from reaching the skin. In many important Organic coupling reactions, it is used as catalysts. Many important derivatives of dibenzalacetone are prepared from the compound for their antioxidant properties.
5. How dibenzalacetone is prepared by the Claisen Schmidt reaction?
Claisen Schmidt reaction is an important organic reaction that involves the condensation of a ketone or aldehyde having an alpha hydrogen with an aromatic carbonyl compound having no alpha hydrogen in presence of an alkali and eliminating water molecule. Dibenzalacetone is prepared using this reaction mechanism when two molecules of benzaldehyde are condensed with one molecule of acetone in presence of sodium hydroxide one molecule of dibenzalacetone is synthesised.
6. What is the colour of Dibenzalacetone and why?
Dibezalacetone is an aromatic compound which is pale yellow in colour. It has a conjugated pi system which means a system where the p orbitals are connected with delocalized electrons. The system usually has alternate double and single bonds since it is an aromatic compound. The conjugated pi system absorbs photons of longer wavelengths or lower energy in the visible region. It can absorb a maximum up to 380 nm which is the blue region light and thus emits yellow which is the complementary colour of blue. Hence it appears to be pale yellow in colour.
7. What is the role of aldehyde without alpha hydrogen in Claisen Reaction?
The Claisen-Schmidt reaction is actually a crossed aldol condensation. The Claisen-Schmidt condensation deals with condensation between a ketone enolate and an aldehyde which serves as the electrophile. The preferable electrophile is the one that contains no alpha hydrogen since it has no proton for deprotonation by an alkali and will not compete to form an enolate. The ketone enolate acts as the nucleophile. The aldehyde electrophile thus binds to the enolate nucleophile. The aldehyde without alpha hydrogens also prevents the formation of undesirable byproducts.
8. What are the precautions to be taken in a chemistry practical?
The only practical classes which need precautions and safety measures in the school level is the chemistry practical since it deals with many inflammable and reactive compounds. The precautions to be taken are:
Do not work on unknown chemical compounds
Always try to use less quantity of reagents in chemical reactions
Always try to avoid skin and eye contact with any chemicals
Try to control the pressure created in a flask by any vigorous reaction by opening the stopper minimally.
Always keep inflammable reagents away from the flame
Never Throw hot acids directly into the sink.
Wear safety glasses and an apron always in a chemical lab.
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