Preparation of Diazonium salts

A class of organic compounds with the general formula RN₂⁺X includes diazonium salts (di means “two,” azo means “nitrogen,” and the suffix -ium denotes a cationic nature) or diazonium compounds (for example, Cl-, Br-, BF₄– ). X is an organic or inorganic anion (for example, Cl–, Br–, BF₄–, etc.). The preparation of diazonium salts is an explosive process and should’ve been carried out with proper laboratory conditions. There are two nitrogen atoms in total, one of which is positively charged as a result. C₆H₅N₂⁺Cl^– benzene diazonium chloride, C₆H₅N₂+HSO₄^– benzene diazonium hydrogen sulfate, and so on are examples of the diazonium salt.

• A diazonium salt is an organic-inorganic compound that can be used in a wide variety of applications. RN₂⁺X is a common way to represent it. X stands for an ion, and R stands for an organic group.
• Diazonium salts typically contain Cl-, Br-, or BF₄^– as X. The N₂⁺ or diazonium group is what gives these salts their names.
• These salts are named as the diazonium suffix is added to the parent hydrocarbon, and then the anion X, such as bromide, is added.

Preparation of Diazonium Salts

• Diazotization or dissociation is the process of converting an organic compound, typically primary aromatic amines, into diazonium salts.

• Because diazonium salts are exceedingly unstable when held at room temperature, they cannot be used after the preparation of diazonium salts.

• One of the most popular ways to prepare diazonium salts is by reacting nitrous acid with aromatic amines.

• When aniline is added to nitrous acid, it is the preparation of benzene diazonium chloride.
• It is common practice to prepare nitrous acid in situ (on the spot) by reacting NaNO₂ with a mineral acid.

• Diazonium salts are stable at temperatures lower than 5°C, which is an important factor in the formation of these salts.

• In order to prevent the diazonium group from decomposing into N₂ as soon as it is formed, the reaction temperature must be kept below 5°C.

• Aniline reacts with NaNO₂ and hydrochloric acid to form benzene diazonium chloride, which is shown in the reaction below.

• NaNO₂+C₆H₅NH₂ +2HCl (Temperature0–5°C)−−−−−−−−−−−→C₆H₇N₂Cl +NaCl+2H₂O

The diazonium group can be used in a variety of applications. When it comes to synthesising various organic compounds, the ability to use both organically-derived and inorganic components has proven invaluable.

Properties of Diazonium Salts

• Ionic in nature, they have a charge of negative ions.
• They can be washed away.
• They are colorless, crystallized solids made of Aryl diazonium salt.
• In water, benzene diazonium chloride dissolves, but it only reacts with it once it has been slightly warmed.
• Insoluble in water is Benzenediazonium Fluoroborate (BF). Temperature-wise, it’s a little more stable.

Importance of Diazonium Salts

• They’re used to make dyed fabrics in the dye and pigment industries.
• Documents can be reproduced using them because of their ability to decompose when exposed to ultraviolet light.
• A wide range of organic compounds can be synthesized using them, particularly aryl derivatives.
• The direct halogenation of aryl iodides and fluorides is ineffective. Chlorobenzene cannot be substituted nucleophilically by a cyano group. Cyanobenzene can be made from diazonium salts, however.
• Direct substitution of aromatic compounds in benzene is not possible. The diazo group is replaced in diazonium salts for these compounds.
• The –F, –Br, –Cl, –I, –NO₂, –OH, and –CN groups are introduced into the aromatic ring via these intermediates.

Conclusion

There are a number of different types of diazonium salts, including RN₂⁺X^– where R is an aryl group and the X^– ion can be Cl, Br, HSO₄, or BF₄^–. The preparation of diazonium salts is one of the important reactions in organic chemistry. After the anion name such as chloride or hydrogen sulfate, the suffix “diazonium” is appended to the name of the parent hydrocarbon from which the diazonium salt is formed. Diazonium salt is the name given to the N₂⁺ group. So, C₆H₅N₂+ Cl^– is referred to as benzene diazonium chloride, and C₆H₅N₂ +  HSO₄ ^– is referred to as benzene diazonium hydrogen sulfate, for example.
When primary aliphatic amines are converted to alkyl diazonium salts, they become very unstable compounds. In solution at low temperatures, primary aromatic amines form arene diazonium salts. However, these salts are only stable for a short time (273-278 K). The stability of the arene diazonium ion can be explained by the resonance principle.
Aniline reacts with nitrous acid at 273K-278 K to produce benzene diazonium chloride.
Sodium nitrite reacts with hydrochloric acid to form nitrous acid in the reaction mixture.
Diazotization is the process of turning primary aromatic amines into diazonium salts. The diazonium salt cannot be stored due to its instability, so it must be used immediately.
C₆H₅NH₂ + NaNO₂ + 2HCl ——- C₆H₅N₂+Cl^– + NaCl +2H₂O (273 – 278K)