Balanced reaction mechanism and laboratory procedure for 2 naphthol aniline dye
2- Naphthol aniline dye is an azo-compound. It is a red-colored dye. It is mainly used for dyeing textiles. Azo compounds have an extended conjugation scheme and they are also colored and used as colors. These compounds are prepared by a reaction known as the coupling reaction. 2-Aniline naphthol dye is made from aniline. In this article, we will study the preparation of 2 naphthol aniline dye in detail.
Preparation of 2 Naphthol Aniline Dye - Practical Experiment
Aim
To prepare 2-Naphthol Aniline Dye from aniline, sodium nitrite, hydrochloric acid and alkaline solution of β-naphthol also called 2-naphthol.
Theory
2- Naphthol aniline dye can be prepared by coupling reaction. In the presence of hydrochloric acid, aniline reacts with sodium nitrite and forms benzene diazonium chloride. A bright orange 2-naphthol aniline dye is formed by additional benzene diazonium chloride reacting with 2-naphthol.
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Azo compounds are prepared under alkaline conditions by the reaction of diazonium salts with phenol. To give a diazonium salt, primary aromatic amines react with nitrous acid at 0oC. In exchange, nitrous acid is formed by a sodium nitrite reaction with hydrochloric acid. Nitrous anhydride or dinitrogen trioxide is an active reagent. Nitrous anhydride reacts with aniline to provide an unstable nitroamine derivative and isomerizes to form a diacetic acid, which is converted into a diazonium salt in turn. Finally, in the presence of sodium hydroxide, this diazonium salt reacts with 2-naphthol to give 2-naphthol aniline, which is an aniline dye.
Materials Required
Aniline
Sodium nitrite
Hydrochloric acid
2-Naphthol
Sodium hydroxide solution
Beaker
Test tube
Buchner funnel
Pipette
Capillary tube
Thermometer
Distilled water
Hot air oven
Ice bath
Procedure
5ml of aniline was dissolved in a mixture of hydrochloric acid and water.
In an ice bath, cool the solution at 0-5 oC.
With constant shaking and monitoring the temperature below 5oC, add a solution of 4gm sodium nitrite in 15ml of water dropwise.
Take another flask to dissolve 8gm of 2-naphthol in a solution of 5 gm sodium hydroxide solution in 50ml of water.
In the ice bath, cool the solution to 0-5oC.
Now mix the two cold solutions dropwise with regular stirring.
Continue stirring for at least half an hour without raising the temperature above 10oC.
It is isolated by an orange azo dye called 2-naphthol aniline.
Filter and wash the crude sample with cold water.
From ethyl alcohol or glacial acetic acid, dry and recrystallize it.
Observations
Result
The 2- Naphthol aniline dye yield is ______ gm.
Precautions
It is important to cool the solution to 5oC. Do not let the temperature increase.
Do not touch the dye as it will stick to your palms. Do not touch
Do not touch the concentrated acids as it can cause irritation.
In order to eliminate soluble impurities, wash the crude sample frequently with cold water.
Keep the pH between 4-5.
Did You Know?
Coupling reaction refers to the class of organic reactions involving the interaction of two chemical species (usually with the help of a metal catalyst). The reaction of an organic halide with an organometallic compound having the general formula R-M that facilitates the formation of a new carbon-carbon bond is an important type of coupling reaction. If the organic halide has the general formula R'-X in this reaction, the compound produced as a result would have the R-R 'formula.
The Coupling Reaction is of Two Types
Homo-coupling reactions
Hetero-coupling reactions (also known as cross-coupling reactions)
Importance of Practical Experiments in Chemistry
Chemistry is an experimental science that needs to be understood more in practical terms than theoretical terms. Practical experiments have a significant role to play as the students learn the different chemical compositions through these. All schools and teachers believe in the benefits of practical experience as seeing something makes you more convinced in terms of understanding its concept. It assists in general evaluation and learning which helps students secure higher marks in their exams. Chemistry is a didactic subject that can only be understood once it is witnessed. Experiments form the core of a subject like Chemistry so that students can pick up whatever they learn in theory faster than usual.
FAQs on Preparation of 2 Naphthol Aniline Dye in Organic Chemistry
1. What is the preparation of 2‑naphthol aniline dye?
The preparation of 2‑naphthol aniline dye involves diazotization of aniline followed by azo coupling with 2‑naphthol to form an azo dye. It occurs in two main steps:
- Step 1: Diazotization – Aniline reacts with sodium nitrite and hydrochloric acid at 0–5°C to form benzenediazonium chloride.
C6H5NH2(aq) + NaNO2(aq) + 2HCl(aq) → C6H5N2+Cl-(aq) + NaCl(aq) + 2H2O(l) - Step 2: Coupling reaction – The diazonium salt reacts with alkaline 2‑naphthol to give an orange‑red azo dye.
2. What is the chemical reaction involved in the preparation of 2‑naphthol aniline dye?
The key chemical reaction is an azo coupling reaction between benzenediazonium chloride and 2‑naphthol in alkaline medium. The simplified reaction is:
C6H5N2+Cl-(aq) + C10H7OH(aq) → C6H5–N=N–C10H6OH(s) + HCl(aq)
- The –N=N– group formed is called the azo group.
- The reaction occurs in cold and alkaline conditions.
3. Why is the temperature maintained at 0–5°C during diazotization?
The temperature is maintained at 0–5°C to prevent decomposition of the unstable diazonium salt. Important reasons include:
- Benzenediazonium chloride decomposes at higher temperatures.
- Low temperature stabilizes the diazonium ion.
- It prevents formation of unwanted by‑products.
4. What is an azo dye in organic chemistry?
An azo dye is an organic compound containing the functional group –N=N– linking two aromatic rings. Key features include:
- Formed by azo coupling reaction.
- Usually brightly colored due to extended conjugation.
- Widely used in textile and dye industries.
5. What is the role of sodium nitrite and hydrochloric acid in this experiment?
Sodium nitrite and hydrochloric acid generate nitrous acid (HNO2) in situ, which converts aniline into a diazonium salt. The reaction is:
NaNO2(aq) + HCl(aq) → HNO2(aq) + NaCl(aq)
- HNO2 reacts with aniline to form benzenediazonium chloride.
- This step is called diazotization.
6. Why is the coupling reaction carried out in alkaline medium?
The coupling reaction is carried out in alkaline medium to increase the reactivity of 2‑naphthol. In basic solution:
- 2‑naphthol forms the naphthoxide ion, which is more nucleophilic.
- The activated aromatic ring reacts readily with the diazonium ion.
7. What is the structure of 2‑naphthol aniline dye?
The structure of 2‑naphthol aniline dye contains two aromatic rings linked by an azo group (–N=N–). Its structural form can be written as:
C6H5–N=N–C10H6OH
- One ring comes from aniline.
- The other ring comes from 2‑naphthol.
8. What type of reaction is involved in the preparation of 2‑naphthol dye?
The preparation involves two main reactions: diazotization and electrophilic aromatic substitution (azo coupling). Specifically:
- Diazotization converts a primary aromatic amine into a diazonium salt.
- Azo coupling is an electrophilic substitution where the diazonium ion acts as an electrophile.
9. What are the uses of 2‑naphthol aniline dye?
2‑naphthol aniline dye is mainly used as a synthetic azo dye in laboratories and textile applications. Its uses include:
- Dyeing cotton and wool fabrics.
- Demonstrating azo coupling reactions in practical chemistry.
- Preparation of pigments and coloring agents.
10. What precautions should be taken during the preparation of 2‑naphthol aniline dye?
Strict temperature control and safe handling of chemicals are essential during dye preparation. Key precautions include:
- Maintain temperature at 0–5°C during diazotization.
- Handle aniline and acids with gloves and goggles.
- Prepare diazonium salt freshly to avoid decomposition.
- Avoid inhalation of vapors in the laboratory.
