Diazonium Salts

Diazonium Compounds, commonly known as diazonium salts. Aryl diazonium salts are frequently used as intermediates in chemical synthesis. The diazonium group is easily replaced by a range of functional groups, allowing the introduction of groups that cannot be directly substituted onto the aromatic ring, such as –I, –OH, –F, –CN, and –H. Furthermore, one can generate substitution patterns that are diametrically opposed to the norm (i.e., preparation of 1,3-disubstituted benzenes). In the majority of these replacements, the diazonium salt is not separated.

 IUPAC Nomenclature Of Diazonium Compounds

They’re known as “Diazonium salts” for a reason (the word di refers to two, aza stands for nitrogen, and the last term onium suggests the ionic nature of the compound). As a result, the term “diazonium salts” refers to ionic compounds containing N≡N. Add “Diazonium” to the name of the aromatic chemical and the anion’s name to identify them.

 Diazonium salts include benzenediazonium chloride (C6H5N2+Cl–), benzene diazonium hydrogen sulphate (C6H5N2+HSO4–), and others.

● Diazonium salts are one of the most flexible organic and inorganic component combinations. It is generally represented as RN2+X. The R indicates an organic group, usually an aryl group, while the X represents an ion.

● X in diazonium salts is typically Cl-, Br-, or BF4. The presence of the N2+ group or the diazonium group gives rise to the names of these salts.

● These salts are named by appending the suffix diazonium to the parent hydrocarbon from which they are formed, followed by the anion X, such as bromide.

 The significance of these chemicals can be found in their applications and usage.

 Preparation of Diazonium Salts

•  When a primary aromatic amine is converted to diazonium salts, a method known as diazotization or dissociation is used instead to get diazonium salt formation.

• Diazonium is a very volatile group, and as a consequence, it is not frequently stored; instead it is consumed shortly after manufacture.

• Reaction of nitrous acid with aromatic amines is one of the most common processes for creating diazonium salt and is widely used. Nitrous acid reacts with aniline (aromatic amine) to produce benzene diazonium chloride as the result of the reaction.

• Nitrous acid is often created by reacting sodium nitrate with a mineral acid in order to prevent the generation of potentially hazardous gases during the operation itself (in situ).

• Because most diazonium salts are stable at temperatures below 5 degrees Celsius, temperature is an important consideration while making these salts.

• To prevent this, the reaction temperature must be kept below 5 degrees. This will cause N2 to be released as soon as the diazonium group is formed.

In the following section, the reaction of aniline with sodium nitrate and hydrochloric acid is described, and the result of the reaction is benzene diazonium chloride (BDC) to get diazonium salt formation. The diazonium group has a wide range of applications. From the dyes and pigments sector to the synthesis of numerous organic molecules, this mix of organic and inorganic components has benefited scientists tremendously. diazonium salt decomposes as:

C6H5N2+Cl−⟶C6H5Cl+N2.

 Diazonium Salts Physical Properties

 Diazonium salts are colourless crystals that darken when exposed to air. Numerous diazonium compounds of nitrates and perchlorates spontaneously combust when heated or struck when dry. As a result, these salts are not separated and are immediately used to synthesise new synthetic medicines. However, double salts of diazonium and zinc chloride and diazonium and tetrafluoroborates are stable at room temperature. They have been used as quick dye salts in the synthesis of naphthol-AS dyestuffs.

 Nitrogen Displacement Reactions

 The most general strategy for incorporating F, Cl, Br, I, CN, OH, and H into an aromatic ring is to substitute the diazonium group. Diazonium salts are advantageous for synthesis because they may be synthesised from nearly all major aromatic amines and react to form a diverse array of compounds. The presence of a few groups in the molecule impairs diazotization; diazonium salts differ from Grignard reagents in this aspect. The amines required to synthesise diazonium compounds are readily available via the direct nitration of nitro compounds.

 Diazonium Salts: Importance in the Synthesis of Aromatic Compounds

Consider some of the applications of diazonium salts in organic synthesis. First, consider some fundamental compounds, such as the three isomeric nitrotoluenes. Diazotization is employed optimally in each of these scenarios, although not for the same reason. To synthesise o- and p-bromoaniline, the corresponding o- and m-nitrotoluenes are utilised.

Diazonium salts are critical in the production of Aromatic Compounds. As previously stated, the advantage of these multi-step synthesis over direct bromination is that a pure product is obtained. Separation of the o- and p-bromoaniline formed by direct bromination is not achievable.The reactions that cause the formation of m-bromotoluene are as follows:

 Diazonium Salts: Their Importance

● They are used in the dye and pigment industries to create coloured materials.

● They are utilised in document reproduction due to their ability to degrade in the presence of UV light.

● They can be used to synthesise various chemical molecules, particularly aryl derivatives.

● Direct halogenation is ineffective for the preparation of aryl iodides and fluorides. It is impossible to replace a cyano group for chlorine in chlorobenzene nucleophilically. However, diazonium ions can be utilised to synthesise cyanobenzene efficiently.

●  Direct substitution of substituted aromatic compounds into benzene is not possible. These compounds are synthesised by substituting the diazo group in diazonium salts.

● They serve as intermediates in introducing the –F, –Br, –Cl, –I, –NO2, –OH, and –CN groups into the aromatic ring.

 Conclusion

Diazonium salts were first synthesised from aromatic amines in 1858. Through the manipulation of the chemical structures of the amines that are diazotized (the diazo components) and the compounds with which they react (the coupling components), dyes that are applicable to many different types of fibres can be dyed with colours spanning the visible spectrum using a variety of different techniques.