Stepwise mechanism of diazotization reaction with conditions and examples
The process of producing diazonium salts or diazonium compounds is called diazotization. It was 1st given by Peter Griess. Thus, diazotization is the process used in the formation of diazonium salts through aromatic amines.
What is Diazotization Reaction?
Aromatic amine reacts with nitrous acid and mineral acid to form diazonium salt and produces water as a side product. This reaction is known as Diazotization Reaction. The reaction can be represented in words reaction form as follows –
Word Reaction Form of Diazotization Reaction – It will help you to remember the reaction easily.
Aromatic Amine + Nitrous Acid + Mineral Acid \[\rightarrow\] Diazonium Salt + Water
Compounds in which an amino or substituted amino group is bonded directly to an aromatic ring are known as aromatic amines. For example –
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Nitrous acid is a weak and monobasic acid which is generally used in the gaseous phase. Its formula is HNO2.
Nitrous Acid Structure :
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Mineral acids are inorganic acids that give hydrogen ions when dissolved with water. Examples of mineral acids are HCl, H2SO4, HBF4 etc.
We can write diazotization reaction in the following form as well –
\[ArNH_2 + HNO_2 + HX \rightarrow RN_2^+X^- + H_2O\]
Aromatic Amine Nitrous Acid Mineral Acid Diazonium salt Water
Example of Diazotization Reaction
Diazotization of Aniline
It is done by treating aniline with sodium nitrate and HCl at a temperature of 273K.
The Reaction Involved is Given Below :
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Diazotization Reaction Mechanism
The Diazotization mechanism can be explained in the following four steps –
Step 1. Formation of Nitrosonium Ion -
Nitrous acid reacts with mineral acid (mineral acid provides hydrogen ion) and forms nitrosonium ion. The reaction is given below-
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Step 2. Formation of N-Nitrosamine -
In this step, Nitrosonium ion reacts with the aromatic amine to give N-nitrosamine. When nitrosonium ion reacts with aromatic amine, its positive charge shifts on the nitrogen of aromatic amine as nitrogen attached with aromatic amine gives its lone pair of electrons to nitrosonium ion. As a result of this, a nitrogen-nitrogen bond is formed between aromatic amine and nitrosonium ions. Now deprotonation takes place which gives N-nitrosamine as a product. The reaction involved is given below –
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Step 3. Formation of Diazohydroxide by Protonation and Deprotonation of N-Nitrosamine
Protonation of N-nitrosamine takes place followed by deprotonation of it. Which gives rise to diazohydroxide.
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Step 4. Formation of Diazonium Ion by Protonation of Diazohydroxide
In this step protonation of diazohydroxide takes place which gives water and diazonium ion. Diazonium ion can be easily converted into diazonium salt.
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Diazotization Titration
Diazotization titration involves a diazotization reaction or formation of diazotization salt. In the diazotization titration process, we 1st weigh the sample and put it in the standard conical flask. Now conc. HCl and KBr are added to the flask and the rest of the volume is filled with distilled water. This resulting solution is a standard solution. Now the appropriate quantity of standard solution is pipette out in another conical flask for titration. The temperature is maintained at 0-5℃. Now the solution is titrated with the NaNO2 solution until starch iodide paper turns blue. It indicates the endpoint.
Uses of Diazonium Compounds
Uses of Diazonium Compounds are as follows –
It is used in the dye and pigment industry.
It is used in document reproduction as these compounds are light-sensitive and break down under UV or violet light.
It is used in the synthesis of organic compounds.
These compounds are used in explosive materials as solid diazonium halides are explosive.
It is used in Fischer indole synthesis of triptan compounds and indomethacin.
It is used in nanotechnology to exfoliate the nanotubes.
It is used in the reaction called Meerwein Arylation which produces phenylated products.
Benefits of Diazonium Compounds in Nanotechnology:
Diazonium Compounds are a key component in the realm of nanotechnology.
Diazonium Compounds are combined with an ionic solvent in a mortar and pestle to exfoliate the nanotubes.
Due to significant cohesive forces between the tubes, dizonium compounds prohibit the tubes from forming intimate bundles, which is a recurring difficulty in nanotube technology.
Conclusion
This article is all about introduction of diazotization reaction, diazotization reaction mechanism, diazotization titration and uses of diazotization compounds.
FAQs on Diazotization Reaction Mechanism in Organic Chemistry
1. What is the diazotization reaction in chemistry?
The diazotization reaction is the conversion of a primary aromatic amine into a diazonium salt using nitrous acid at low temperature (0–5°C).
In this reaction:
- A primary aromatic amine (e.g., aniline, C6H5NH2) reacts with nitrous acid (HNO2), generated in situ from NaNO2 and HCl.
- The product formed is a benzene diazonium salt (C6H5N2+Cl-).
2. What is the mechanism of the diazotization reaction?
The diazotization mechanism involves formation of a nitrosonium ion followed by substitution of the amine group to form a diazonium salt.
Main steps:
- Step 1: NaNO2 + HCl → HNO2 (formation of nitrous acid).
- Step 2: HNO2 + H+ → NO+ + H2O (formation of nitrosonium ion).
- Step 3: The aromatic amine reacts with NO+ to form a diazonium ion.
- Step 4: The diazonium ion combines with Cl- to give the diazonium salt.
3. What is the balanced chemical equation for the diazotization of aniline?
The balanced equation for diazotization of aniline is:
C6H5NH2(aq) + NaNO2(aq) + 2HCl(aq) → C6H5N2+Cl-(aq) + NaCl(aq) + 2H2O(l)
Key points:
- Aniline is converted into benzene diazonium chloride.
- Nitrous acid is generated in situ from NaNO2 and HCl.
- The reaction is performed at 0–5°C.
4. Why is the diazotization reaction carried out at 0–5°C?
The diazotization reaction is carried out at 0–5°C to prevent decomposition of the diazonium salt.
Reasons:
- Aromatic diazonium salts are stable only at low temperatures.
- At higher temperatures, they decompose to form phenols or release N2 gas.
- Low temperature ensures better yield and controlled reaction.
5. What are diazonium salts and why are they important?
Diazonium salts are organic compounds containing the functional group –N2+ attached to an aromatic ring.
General formula: Ar–N2+X-
- Ar = aromatic group
- X- = Cl-, Br-, etc.
- Used in azo dye synthesis.
- Participate in Sandmeyer and other substitution reactions.
- Help introduce –Cl, –Br, –CN, –OH groups into aromatic rings.
6. What reagents are required for the diazotization reaction?
The main reagents required for diazotization are a primary aromatic amine, sodium nitrite (NaNO2), and a mineral acid such as HCl.
Reagent roles:
- Primary aromatic amine (e.g., aniline) – starting compound.
- NaNO2 – generates nitrous acid.
- HCl – provides acidic medium and forms diazonium chloride.
7. Can aliphatic amines undergo diazotization?
No, aliphatic amines do not form stable diazonium salts under diazotization conditions.
Explanation:
- Aliphatic diazonium salts are highly unstable.
- They decompose immediately to form alcohols and release N2 gas.
- Only primary aromatic amines form relatively stable diazonium salts.
8. What is the role of nitrous acid in diazotization?
Nitrous acid (HNO2) provides the nitrosonium ion (NO+), which is the active electrophile in diazotization.
Key steps:
- NaNO2 + HCl → HNO2
- HNO2 + H+ → NO+ + H2O
- NO+ reacts with the aromatic amine to form the diazonium ion.
9. What is the difference between diazotization and azo coupling?
Diazotization forms a diazonium salt, while azo coupling uses that diazonium salt to form an azo compound.
Differences:
- Diazotization: Ar–NH2 → Ar–N2+X-
- Azo coupling: Ar–N2+ reacts with phenol or aniline to form Ar–N=N–Ar′
- Diazotization is a preparation step; azo coupling produces colored azo dyes.
10. What are the common uses of the diazotization reaction?
The diazotization reaction is mainly used to prepare azo dyes and substituted aromatic compounds.
Main applications:
- Manufacture of textile dyes and pigments.
- Sandmeyer reaction to introduce –Cl, –Br, –CN groups.
- Preparation of phenols from aromatic amines.
- Synthesis of pharmaceuticals and fine chemicals.
