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Diazotization is the process of producing a diazonium salt or diazonium compound. It is an organic reaction in which an aromatic amine reacts with a reagent containing a nitrosyl cation (NO) or a reagent capable of producing the corresponding aryldiazonium salt. It was first discovered by Peter Griess. Diazotization is the process used to form diazonium salts with aromatic amines. Diazotization of bifunctional aromatic amines (eg, p-phenylenediamine or benzidine) is also called "tetrazotization".
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Key Terms: Aromatic amines, diazonium salts, Compounds, chemical reactions, nitrous acid, amines, tetrazotization, aromatic ring, amino group
Diazotization Reaction
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Aromatic amines react with nitric acid and mineral acids to form diazonium salts, producing water as a by-product. This reaction is known as the diazotization reaction. Reactions can be expressed in words in reaction form as follows:
Mineral Acid + Aromatic Amine + Nitrous Acid -> Water + Diazonium Salt
Compounds in which an amino group or a substituted amino group is directly attached to an aromatic ring are known as aromatic amines. For example-
The video below explains this:
Diazotization Reaction Detailed Video Explanation:
Aromatic Amines
Nitrous acid is a weak monobasic acid commonly used in the gas phase. The formula is HNO2.
Mineral acid is an inorganic acid that releases hydrogen ions when dissolved in water. Examples of mineral acids are HCl, H2SO4, HBF4 and so on. Diazotization reaction can be written as:
Examples:
- Aniline’s Diazotization
This is done by treating the Aniline with sodium nitrate and HCl at a temperature of 273K.
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Mechanism of Diazotization Reaction
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The mechanism of diazotization can be explained in the following four steps.
- Formation of Nitronium Ions
Nitric acid reacts with mineral acids (mineral acids provide hydrogen ions to form nitronium ions.
Formation of Nitronium Ions
- Formation of N-nitrosamines
In this step, nitrosonium ions react with aromatic amines to produce N-nitrosamines. When the nitrosonium ion reacts with the aromatic amine, its positive charge shifts to the nitrogen of the aromatic amine when the nitrogen attached to the aromatic amine gives the nitrosonium ion only a few electrons. As a result, a nitrogen-nitrogen bond is formed between the aromatic amine and the nitrosonium ion. Deprotonation occurs and the product is N-nitrosamines.
Formation of N-nitrosamines
- Formation of diazohydroxide by protonation and deprotonation of N-nitrosamines
Protonation of N-nitrosamines occurs, followed by its deprotonation. This leads to diazo hydroxides.
Formation of diazohydroxide by protonation and deprotonation of N-nitrosamines
- Formation of Diazonium Ions by Protonation of Diazo Hydroxides
In this step, diazohydroxide is protonated to produce water and diazonium ions. Diazonium ions can be easily converted to diazonium salts.
Formation of Diazonium Ions by Protonation of Diazo Hydroxides
Titration of Diazotization
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Diazotization titration involves a diazotization reaction or the formation of a diazotized salt. In the diazotization titration process, the sample is first weighed and placed in a standard Erlenmeyer flask. Now Add Concentrated HCl and KBr to the flask and fill the remaining volume with distilled water.
Titration of Diazotization
This solution is a standard solution. Then pipette the appropriate amount of standard solution into another Erlenmeyer flask for titration. The temperature is kept at 0-5 ° C. The solution is then titrated with a NaNO2 solution until the starch iodide paper turns blue. It shows the endpoint.
Diazonium Compound and Applications
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The usage of diazonium compounds is as follows.
- Used in the dye and pigment industry.
- These compounds are light-sensitive and decompose under ultraviolet or violet light, so they are used in document duplication.
- Used for the synthesis of organic compounds.
- These compounds are used in explosive materials because solid halogenated diazoniums are explosive in nature.
- Used for Fischer indole synthesis of triptan and indomethacin compounds.
- Used in nanotechnology to remove nanotubes.
- It is used in a reaction called Meerwein Arylation and products like phenylated ones are produced.
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Things to Remember
- Diazotization is the process of producing a diazonium salt or diazonium compound. It is an organic reaction in which an aromatic amine reacts with a reagent containing a nitrosyl cation (NO) or a reagent capable of producing the corresponding aryldiazonium salt. It was first discovered by Peter Griess.
- Diazotization of bifunctional aromatic amines (eg, p-phenylenediamine or benzidine) is also called "tetrazotization".
- Aromatic amines react with nitric acid and mineral acids to form diazonium salts, producing water as a by-product. This reaction is known as the diazotization reaction.
Mineral Acid + Aromatic Amine + Nitrous Acid -> Water + Diazonium Salt
- Diazotization titration involves a diazotization reaction or the formation of a diazotized salt.
- The usage of diazonium compounds is of various kinds like They are used in the dye and pigment industry. These compounds are light-sensitive and decompose under ultraviolet or violet light, so they are used in document duplication. They are used for the synthesis of organic compounds.
Sample Questions
Ques: How are diazonium salts made from aniline? (3 marks)
Ans: Benzene is very stable and less reactive, making it very difficult to prepare various aromatic compounds from benzene.
However, since many aromatic derivatives can be produced from highly reactive diazonium salts, diazonium salts are often used as a raw material for preparing various aromatic hydrocarbons.
Diazonium salts are prepared by a diazotization reaction. In this reaction, aniline is treated with NaNO2 and HCl at low temperatures to form the benzene diazonium chloride.
Ques: How is aniline converted to carbonic acid? (1 marks)
Ans: When aniline reacts with NaNO2 and HCl at low temperatures, diazotization occurs and benzene diazonium chloride is produced. The diazonium salt thus obtained is hydrolyzed to phenol.
Ques: What is the Balz-Schiemann reaction? (2 marks)
Ans: Diazotization of induced tetrafluoroborate or hexafluorophosphate followed by thermal decomposition conversion of arylamines to aryl fluorides. Degradation can also be photochemically triggered.
Ques: What are the coupling reaction and diazotization factors? (3 marks)
Ans: Prepare synthetic dyes using diazotization and coupling reactions Ariel diazonium salts that are water-soluble by diazotizing aromatic primary amines with nitric acid (0-4 ° C) and nitric acid (NaNO2 dil. HCl). And form a clear solution dye. This clear solution is added to an ice-cold alkaline solution of the phenolic compound and mixed well to give a red dye.
Ques: What happens if I add a mixture of aniline and dilute hydrochloric acid to a solution of sodium nitrite in the AZO colour test? (3 marks)
Ans: Nothing happens!
Because diazotization requires cold environments, Below 5 degrees Celsius, Benzene diazonium chloride is obtained. It is colourless.
Lower the temperature again. Then, it is necessary to start the coupling reaction between diazonium chloride and aromatic amines containing auxiliary chromium.
Ques: What is the effect of benzene diazonium chloride on aniline? (2 marks)
Ans: diazotization occurs by substituting hydrogen of NH2 contained in aniline with chlorine of benzene diazonium chloride to form a complex derived from Azoderivative.
Ques: How can our ortho-chloro nitro benzene be made from nitrobenzene? (3 marks)
Ans: Nitro benzene of chlorobenzene produces nitrobenzene, a mixture of ortho chloro benzene and paradichlorobenzene. Separation results in ortho chloronitrobenzene.
Chlorobenzene can be obtained from nitrobenzene by following the steps below.
- Nitrobenzene is reduced to aniline using Sn / HCl.
- Aniline diazotized with NaNO2 / HCl produces benzene diazonium chloride.
- Benzenediazonium chloride in CuCl / HCl-treated benzene produces chlorobenzene (Sandmeyer reaction).
Ques: How can I make an azo dye? (3 marks)
Ans: Phase 1- Diazotization
This is a primary aromatic amine called the diazo component. Treated with sodium nitrite under cold acidic conditions, it forms an unstable diazonium salt.
Phase 2- Azo Coupling
Diazonium salts react with coupling components (e.g. phenols or aromatic amines). Form a stable azo dye.
Ques: Why is only one aromatic amine diazotized? (3 marks)
Ans: Treatment of PhNH2 with NaNO2 + HCl / 0–5 ° C gives PhN2+Cl-.
Since PhNHCH3 has only one hydrogen in nitrogen, N-nitroso-N-methyl aniline can be obtained.
Since PhN(CH3)2 does not contain hydrogen in nitrogen, it undergoes an electrophilic substitution reaction to produce para-nitroso-N and N-dimethylaniline.
Therefore, only primary amines undergo a diazotization reaction.
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