Detailed Procedure for Preparation of Acetanilide with Explanation
The Preparation of Acetanilide is a widely performed organic synthesis experiment in chemistry. Acetanilide is an aromatic amide used as an intermediate in pharmaceuticals, dyes, and as a stabilizer. This article explores the method for the preparation of acetanilide from aniline, elucidates its chemical reaction mechanism, and outlines key aspects relevant to laboratory synthesis.
Acetanilide: Structure and Importance
Acetanilide (C8H9NO) is an aromatic amide formed by the acetylation of aniline. It consists of a benzene ring attached to an amide functional group.
- Acetanilide is produced by replacing one hydrogen atom of the amine group in aniline with an acetyl group.
- It is significant as a precursor in dyes and medicines, and is also used in research and industrial applications.
Preparation of Acetanilide from Aniline
The most common method for the preparation of acetanilide from aniline involves acetylation, typically using acetic anhydride or acetyl chloride as the acetylating agent.
Materials and Reagents
- Aniline ($C_6H_5NH_2$)
- Acetic anhydride or acetyl chloride
- Glacial acetic acid (as solvent and catalyst)
- Distilled water
Step-by-Step Procedure
- Dissolve aniline in glacial acetic acid to form a clear solution.
- Add acetic anhydride (or acetyl chloride) slowly with stirring to the solution.
- Mix thoroughly. The exothermic reaction leads to the formation of acetanilide and acetic acid as a byproduct.
- Pour the reaction mixture into cold water to precipitate acetanilide.
- Filter and purify the crude acetanilide by recrystallization.
The overall chemical equation for this process is:
$$ C_6H_5NH_2 + (CH_3CO)_2O \rightarrow C_6H_5NHCOCH_3 + CH_3COOH $$
Mechanism of Acetanilide Formation
The preparation of acetanilide from aniline mechanism follows a nucleophilic acyl substitution:
- The lone pair on aniline nitrogen attacks the carbonyl carbon of acetic anhydride (or acetyl chloride).
- This forms a tetrahedral intermediate.
- Elimination of acetic acid (or HCl if acetyl chloride is used) gives acetanilide.
Alternative Methods and Variations
- Preparation of acetanilide from aniline and acetyl chloride is known as acetylation as well.
- Industrial synthesis occasionally uses other acylating agents for efficiency or yield improvements.
For more about related acetylation reactions, you may explore acetylation mechanisms. Understanding the types of organic reactions deepens insight into this process. Additionally, knowledge of benzene ring reactions is beneficial for comprehending similar aromatic compound syntheses.
Crystallization and Purification
After precipitation, acetanilide is purified by recrystallization:
- Dissolve crude product in hot water.
- Filter to remove insoluble impurities.
- Cool to allow pure acetanilide crystals to form.
Other Preparative Routes
While the most common route is from aniline, preparation of acetanilide from acetophenone involves more complex organic synthesis and is less frequently used in basic labs.
You can also read about preparation of benzene for context on aromatic compound synthesis.
Key Safety Tips
- Always perform reactions in a fume hood due to volatile chemicals and potential irritants.
- Wear proper lab safety gear such as gloves and goggles.
For fundamental concepts needed to understand this experiment, review organic compounds and their properties.
The preparation of acetanilide is an essential experiment highlighting acetylation reactions and nucleophilic acyl substitution mechanisms. Whether approached through acetic anhydride or acetyl chloride, understanding the preparation, mechanism, and purification process reinforces major organic chemistry concepts. Mastery of this reaction supports comprehension of both laboratory and industrial aromatic amide synthesis, especially for key intermediates like acetanilide. Further study of the preparation of acetanilide from aniline and related topics is pivotal for students and professionals in organic chemistry.
FAQs on How to Prepare Acetanilide in the Laboratory
1. What is the preparation of acetanilide?
Acetanilide is prepared by the acetylation of aniline with acetic anhydride in the presence of glacial acetic acid or concentrated sulfuric acid as a catalyst. The process involves:
- Mixing aniline and acetic anhydride in a suitable flask
- Adding glacial acetic acid or sulfuric acid to catalyse the reaction
- Gently heating until a solid precipitate of acetanilide forms
- Isolating the product by filtration and washing
- Purifying the product by recrystallization from hot water
2. What is the principle of preparation of acetanilide from aniline?
The preparation of acetanilide from aniline is based on the principle of acetylation, where the amino group (-NH2) in aniline reacts with acetic anhydride to form an amide. The main steps are:
- Replacement of a hydrogen atom of the amine group in aniline by an acetyl group
- Formation of acetanilide and acetic acid as a byproduct
3. What are the materials required for the preparation of acetanilide in a laboratory?
To prepare acetanilide in the lab, you need:
- Aniline
- Acetic anhydride
- Glacial acetic acid (or concentrated sulphuric acid)
- Water (for recrystallization)
- Beaker, glass rod, funnel, filter paper, and heating apparatus
4. Describe the procedure for the laboratory preparation of acetanilide from aniline.
The laboratory preparation of acetanilide involves several steps for pure product formation:
- Take a small quantity of aniline in a beaker
- Add an equal amount of acetic anhydride and a few drops of glacial acetic acid
- Stir the mixture and warm gently in a water bath for 10–15 minutes
- Upon cooling, crystalline acetanilide separates out
- Filter, wash with cold water, and dry the crude product
- Purify by recrystallization from hot water
5. What is the chemical equation for the synthesis of acetanilide from aniline?
The chemical equation for the formation of acetanilide is:
Aniline + Acetic anhydride → Acetanilide + Acetic acid
C6H5NH2 + (CH3CO)2O → C6H5NHCOCH3 + CH3COOH
This highlights the acetylation reaction central to acetanilide preparation for board exams.
6. Why is glacial acetic acid used in the preparation of acetanilide?
Glacial acetic acid acts both as a solvent and a catalyst during the synthesis:
- It helps dissolve both aniline and acetic anhydride for better mixing
- Catalyses the acetylation reaction for improved yield of acetanilide
- Minimizes side reactions for purer product
7. How is crude acetanilide purified after synthesis?
Crude acetanilide is generally purified by recrystallization from hot water:
- Dissolve the crude product in minimum hot water
- Filter if any insoluble impurities are present
- Cool the filtrate to allow pure acetanilide crystals to form
- Filter and dry the crystals to obtain pure acetanilide
8. What are the uses of acetanilide?
Acetanilide has multiple uses in academics and industry:
- Intermediate in the synthesis of pharmaceuticals
- Precursor for dyes, plastics, and rubber chemicals
- Reference compound in organic qualitative analysis
- Study material in laboratory experiments and CBSE syllabus
9. What safety precautions should be followed in the preparation of acetanilide?
Key safety precautions when preparing acetanilide in the laboratory:
- Always wear gloves, goggles, and a lab coat
- Avoid inhaling fumes of aniline and acetic anhydride
- Conduct the experiment in a well-ventilated area
- Handle chemicals carefully and avoid skin contact
- Dispose of waste properly, following school lab protocols
10. What observations are made during the preparation of acetanilide?
During the synthesis of acetanilide, students commonly observe:
- Mixing of reactants produces slight heat
- Upon gentle heating, solution becomes clear
- On cooling, white crystalline acetanilide separates out
- Washing and recrystallization yield pure, needle-shaped crystals
11. Which method is used for the preparation of acetanilide?
The standard method for acetanilide synthesis is the acetylation of aniline using acetic anhydride and glacial acetic acid as described in CBSE textbooks and practical manuals.
