Stepwise Diazotization Reaction Mechanism with 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 Explained
1. What is the diazotization reaction in simple terms?
The diazotization reaction is a chemical process that converts a primary aromatic amine (like aniline) into a diazonium salt. This is achieved by reacting the amine with nitrous acid (HNO₂), which is typically generated in the reaction mixture itself at a very low temperature (0-5°C).
2. What are the essential reagents needed to carry out a diazotization reaction?
To successfully perform a diazotization reaction, you need three main components:
- A primary aromatic amine (e.g., aniline).
- Sodium nitrite (NaNO₂).
- A strong mineral acid, most commonly hydrochloric acid (HCl) or sulfuric acid (H₂SO₄).
3. Could you explain the step-by-step mechanism of the diazotization reaction?
The mechanism involves several key steps:
- Step 1: The mineral acid (like HCl) protonates the sodium nitrite to form nitrous acid (HONO).
- Step 2: A second protonation of nitrous acid leads to the loss of a water molecule, forming the highly reactive nitrosonium ion (NO⁺), which acts as the electrophile.
- Step 3: The lone pair of electrons on the nitrogen atom of the primary amine attacks the nitrosonium ion.
- Step 4: A series of proton transfers and the elimination of a water molecule occur, ultimately leading to the formation of the diazonium salt with its characteristic N≡N triple bond.
4. What are some key properties of the diazonium salts that are formed?
Aryl diazonium salts have several distinct properties:
- They are generally colourless, crystalline solids.
- They are readily soluble in water.
- They are stable only at low temperatures (below 5°C) in solution.
- When dry, they are highly unstable and can be explosive, so they are almost always used immediately in solution after being prepared.
5. Why is it so crucial to maintain a very low temperature (0-5°C) during this reaction?
Maintaining a low temperature is critical because diazonium salts are highly unstable. Above 5°C, the diazonium salt will readily decompose, reacting with water to form a phenol and releasing nitrogen gas. This side reaction would prevent the desired synthesis. The cold condition stabilises the diazonium salt, allowing it to be used as an intermediate for other chemical transformations.
6. How do aromatic diazonium salts differ from aliphatic ones in terms of stability?
Aromatic diazonium salts are significantly more stable than their aliphatic counterparts. This stability is due to resonance, where the positive charge on the diazonium group is delocalised across the benzene ring. Aliphatic diazonium salts lack this resonance stabilisation and are extremely unstable, decomposing instantly even at low temperatures to release nitrogen gas. This makes them much less useful in synthetic chemistry.
7. What makes diazonium salts so important in synthetic organic chemistry?
Their importance stems from the diazonium group (–N₂⁺) being an excellent leaving group. It leaves as a very stable, neutral nitrogen molecule (N₂). This property allows the diazonium group to be easily replaced by a wide variety of other atoms or functional groups (like –Cl, –Br, –CN, –OH), making it a versatile bridge to synthesise many different aromatic compounds that are otherwise difficult to prepare.
8. Can you use the diazotization of aniline as a classic example?
Yes, the reaction of aniline is a textbook example. When aniline (C₆H₅NH₂) is treated with sodium nitrite and hydrochloric acid at 0-5°C, it forms benzenediazonium chloride (C₆H₅N₂⁺Cl⁻). This specific product is a key intermediate used in many named reactions, including the Sandmeyer and Gattermann reactions, to introduce different functional groups onto the benzene ring.
