Diazonium Salt Methods of Preparation

Diazonium salts are one of the most versatile combinations of organic and inorganic components. Its general way of representation is \(R-N_{2}^{+}\;X^{-}\). The R is an organic group, generally an aryl group while X represents ion. Generally diazonium salts have Cl, Br, \(BF_{4}^{-}\), as X. The name of these salts is based on the presence of \(N_{2}^{+}\) group or the diazonium group. The naming of these salts is done by adding the suffix diazonium to the parent hydrocarbon from which they are derived and then it is followed by the anion X such as bromide. The importance of these compounds lies in their application and uses. Let us discuss the method with which diazonium salt is prepared.

Method of Preparation of Diazonium Salt

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 diazonium group is highly unstable under normal conditions and hence it is not generally stored, most of the times 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 \(NaNO_2\) with a mineral acid. Another important parameter that governs the product formation during 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 \(N_2\) as soon as it is formed. The reaction of aniline with \(NaNO_2\) and hydrochloric acid is given below, the product of the reaction is benzene diazonium chloride.

\( \require{AMScd} \begin{CD} C_6H_5NH_2 + NaNO_2+ 2HCl @> Temperature 0 – 5^\circ C >> C_6H_5N^+- Cl + NaCl + 2H_2O\end{CD} \)

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. Log on to BYJU’s to explore more about the diazonium salts.


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In the reaction shown below, the major product(s) formed is/are

                                                                              (IIT-JEE Advanced, 2014)