How is Aniline Yellow Prepared Reaction Mechanism Equation and Conditions
Aim
To prepare Aniline yellow (also called as para amino azobenzene) from benzene diazonium chloride and aniline.
Apparatus Required
Aniline
Sodium nitrite
Hydrochloric acid
Distilled water
Glacial acetic acid
Bunsen burner
Round bottom flask
Stirrer
Beaker
Funnel
Conical flask
Water bath
Theory
Aniline yellow is an unstable compound that is used as an intermediate for preparing other dyes. Aniline yellow (para amino azobenzene) is prepared by the coupling reaction between benzene diazonium chloride and aniline in an acidic medium. The dye has no industrial significance because it is an acid-sensitive dye.
The Chemical Reaction Involved
Step 1: When aniline is treated with sodium nitrite in the presence of acid.
Ar-NH2 + NaNO2 + HCl → Ar-N2+ -Cl-
Aniline Sodium Hydrochloric Benzene
Nitrite Acid diazonium chloride
Step 2: Ar-N2+ - Cl- + Ar-NH2 → Ar-N=N-NH-Ar
Step 3: Ar-N=N-NH-Ar → Ar-N=N-Ar-NH2
Aniline Yellow
In the first step, aniline acts as a nucleophile and reacts with benzene diazonium chloride to form a C-N bond. The product loses H+ and gives the azo dye.
Procedure
First of all, take a 10ml concentrated hydrochloric acid (HCl) and 20ml water in a beaker and add4.5ml aniline to the mixture. Dissolve them thoroughly to get a clear solution.
Cool the solution in an ice bath around 5°C. Mix 4gsodium nitrite with 20ml water and add this sodium nitrite solution to the above mixture by doing the constant stirring.
After some time, Diazotization will take place and the formation of benzene diazonium will occur.
Now, Prepare 4ml aniline in 4ml HCl and mix the aniline solution with benzene diazonium chloride solution by slow constant stirring.
After some time, a yellow precipitate of para amino azobenzene which is also called aniline yellow is formed. Filter the yellow precipitate with a Buchner funnel and dry the crude sample in between the folds of paper.
The crude sample can be recrystallized by dissolving in carbon tetrachloride to get the pure dye.
Setup
(Image to be added soon)
Observations
Result
Aniline yellow is produced in _____ gm.
Precautions
Wear lab coats, gloves, and goggles.
Try to maintain a pH of reaction between 4-5.
The temperature of the experiment should range between 40°C to 50°C.
The crude sample should be washed repeatedly by water.
Fun Fact
Preparation of Aniline yellow can be done in the home also. In place of the Buchner funnel, an alternate home-designed suction funnel and plastic bottles can be used. can be used. To maintain the temperature approx 5°C , ice cubes can be used to settle down the solution.
FAQs on Preparation of Aniline Yellow through Diazotization Reaction
1. What is the preparation of Aniline Yellow in chemistry?
The preparation of Aniline Yellow involves diazotization of aniline followed by azo coupling with another molecule of aniline to form p-aminoazobenzene.
It occurs in two main steps:
- Step 1: Diazotization – Aniline reacts with nitrous acid at 0–5°C.
C6H5NH2(aq) + NaNO2(aq) + 2HCl(aq) → C6H5N2+Cl-(aq) + NaCl(aq) + 2H2O(l) - Step 2: Azo coupling – The benzene diazonium chloride couples with aniline in acidic medium to form Aniline Yellow.
C6H5N2+Cl- + C6H5NH2 → C6H5–N=N–C6H4NH2 + HCl
2. What is the chemical formula of Aniline Yellow?
The chemical formula of Aniline Yellow (p-aminoazobenzene) is C12H11N3.
Its structure contains:
- An azo group (–N=N–)
- Two benzene rings
- An –NH2 group in the para position
3. How is benzene diazonium chloride prepared for Aniline Yellow?
Benzene diazonium chloride is prepared by diazotizing aniline with nitrous acid at low temperature (0–5°C).
The balanced reaction is:
C6H5NH2(aq) + NaNO2(aq) + 2HCl(aq) → C6H5N2+Cl-(aq) + NaCl(aq) + 2H2O(l)
Key conditions:
- Temperature maintained at 0–5°C
- Acidic medium (HCl)
- Freshly prepared nitrous acid (NaNO2 + HCl)
4. What is the role of low temperature in the preparation of Aniline Yellow?
Low temperature (0–5°C) is required to stabilize the benzene diazonium chloride formed during diazotization.
If the temperature rises:
- The diazonium salt decomposes
- Nitrogen gas (N2) may be released
- Side reactions reduce yield
5. What type of reaction is involved in the formation of Aniline Yellow?
The formation of Aniline Yellow involves an azo coupling reaction, which is an electrophilic substitution reaction.
In this reaction:
- The diazonium ion (C6H5N2+) acts as an electrophile
- Aniline acts as the activated aromatic compound
- A new –N=N– (azo linkage) is formed
6. Why is Aniline Yellow classified as an azo dye?
Aniline Yellow is classified as an azo dye because it contains the characteristic azo group (–N=N–) linking two aromatic rings.
Azo dyes:
- Contain one or more –N=N– groups
- Show bright colors due to extended conjugation
- Are widely used as synthetic dyes
7. What are the steps involved in the laboratory preparation of Aniline Yellow?
The laboratory preparation of Aniline Yellow involves diazotization followed by coupling.
Procedure steps:
- Dissolve aniline in dilute HCl and cool to 0–5°C.
- Add cold sodium nitrite solution slowly to form benzene diazonium chloride.
- Prepare a separate acidic solution of aniline.
- Add the diazonium solution slowly to the aniline solution with stirring.
- A yellow precipitate of p-aminoazobenzene forms.
8. What is the balanced equation for the azo coupling reaction in Aniline Yellow preparation?
The balanced azo coupling reaction forming Aniline Yellow is:
C6H5N2+Cl- + C6H5NH2 → C6H5–N=N–C6H4NH2 + HCl
Here:
- Benzene diazonium chloride reacts with aniline
- An azo bond (–N=N–) is formed
- The product is p-aminoazobenzene (Aniline Yellow)
9. What are the uses of Aniline Yellow?
Aniline Yellow is primarily used as a synthetic azo dye for coloring textiles and leather.
Common uses include:
- Dyeing silk and wool
- Coloring oils and varnishes
- Research and laboratory demonstrations of azo coupling
10. What precautions should be taken during the preparation of Aniline Yellow?
During the preparation of Aniline Yellow, temperature control and safe handling of chemicals are essential.
Important precautions:
- Maintain temperature at 0–5°C during diazotization.
- Handle aniline carefully as it is toxic.
- Prepare nitrous acid freshly (NaNO2 + HCl).
- Avoid overheating to prevent decomposition of diazonium salt.
