What are Diazonium Salts ? It's Method of Preparation and Properties

Diazonium salts are a group of organic compounds which shares one common functional group R-N + 2X. In R-N + 2X, R is an organic group. The diazonium salts :- (di refers to ‘two’, azo is indicative of ‘nitrogen’ and ium implies that it is cationic in nature),

What are Diazonium Salts?

The diazonium salts or diazonium compounds are the class of organic compounds with general formula R−N2+X−. Here, X is an organic or inorganic anion (for example, Cl–, Br–, BF4–, etc.) and R is an alkyl or aryl group. The term is derived from two words. ‘di’ refers to ‘two’, azo is indicative of ‘nitrogen’ and ium implies that it is cationic in nature.

Hence, they have two nitrogen atoms with one being charged. Benzenediazonium chloride (C6H5N2+Cl–), benzene diazonium hydrogen sulfate (C6H5N2+HSO4–), etc. are some of the examples of the diazonium salt.

Preparation of Diazonium Salts

• The process of converting an organic compound, generally primary aromatic amines, into diazonium salts is referred to as diazotization or dissociation.
• It has been seen that the diazonium group is highly unstable under normal conditions and hence it is not generally stored, most of the time it is used just after its preparation.
• One of the most common methods of preparation of diazonium salt is by reacting nitrous acid with aromatic amines. The reaction of aniline (aromatic amine) with nitrous acid results in the diazonium salt formation that is benzene diazonium chloride.
• Nitrous acid is a highly toxic gas and hence it is generally prepared during the reaction itself (in situ) by reacting NaNO2 with a mineral acid.
• Another important parameter that governs the product formation during the preparation of these salts is temperature; most diazonium salts are stable below the temperature of 5o C.
• It is, therefore, important to keep the reaction conditions below 5oC or else the diazonium group will decompose to give N2 as soon as it is formed.

The reaction of aniline with NaNO2 and hydrochloric acid is given below, the product of the reaction is benzene diazonium chloride.

The diazonium group finds application in many ways. From dyes and pigment industry to synthesis of various organic compounds, this combination of organic and inorganic components has been a boon for the scientists.

Properties of Diazonium Salts

• They are ionic in nature.
• They are water soluble.
• Aryl diazonium salts are colourless crystalline solids.
• Benzenediazonium chloride is soluble in water. But, it reacts with it only when warmed.
• Benzenediazonium fluoroborate is not soluble in water. It is pretty stable at room temperature. So, where do we use these salts? Do you know about its applications? Let us see below.