The diazonium salts (di refers to ‘two’, azo is indicative of ‘nitrogen’ and ium implies that it is cationic in nature), or diazonium compounds, are the class of organic compounds with general formula R−N2+X− where X is an organic or inorganic anion (for example, Cl–, Br–, BF4–, etc.) and R is an alkyl or aryl group.
Hence, they have two nitrogen atoms with one being charged. Benzenediazonium chloride (C6H5N2+Cl–), benzenediazonium hydrogensulphate (C6H5N2+HSO4–), etc. are some of the examples of the diazonium salt.
They are ionic in nature.
They are water soluble.
Aryl diazonium salts are colorless crystalline solids.
Benzenediazonium chloride is soluble in water but reacts with it only when warmed.
Benzenediazonium fluoroborate is not soluble in water. It is pretty stable at room temperature.
They find application in the dye and pigment industries and are used to produce dyed fabrics.
Due to their property of breaking down near the ultraviolet light, they are used in document reproduction
They are useful in the synthesis of a large variety of organic compounds, especially aryl derivatives.
Direct halogenation is not a suitable method for preparing aryl iodides and fluorides. Nucleophilic substitution of chlorine in chlorobenzene by a cyano group is not possible. However, diazonium salts can easily be used to produce cyanobenzene.
It is not possible to prepare substituted aromatic compounds by direct substitution in benzene. For these compounds, we use replacement of diazo group in diazonium salts.
They are used as intermediates for introducing –F, –Br, –Cl, –I, –NO2, –OH and –CN groups into the aromatic ring.