Diazonium salts are a group of organic compounds which share a common functional group R – N2+ X– where R is any organic residue such as alkyl or aryl group, X is organic or inorganic anion such as halogens. The naming of diazonium salts is done by adding a suffix diazonium to the parent hydrocarbon from which they are formed, followed by the name of the anion such as chloride or hydrogensulphate. For example C6H5N2+Cl– is named as benzenediazonium chloride. They are colourless crystalline solid which are readily soluble in water. They decompose easily in dry state.
Chemical reactions of diazonium salts
Diazonium salts undergo two major reactions, but here we will only consider the reactions involving the retention of diazo group.
The azo products obtained in this case have an extended conjugate system which has both the aromatic rings joined through the -N=N- bond. These compounds are generally colored and are often used as dyes. Phenol reacts with benzene diazonium chloride in which the phenol molecule at its para position is coupled with the diazonium salt in order to form p-hydroxyazobenzene. This kind of reaction is often known as coupling reaction. Similarly when diazonium salt reacts with aniline it produces p-aminoazobenzene. This reaction is an example of electrophilic substitution reaction.
Significance of diazonium salts in the synthesis of aromatic compounds
In the above case it is clearly shown that diazonium salts are very good intermediates for the introduction of -F, -Cl, -Br, -I, -CN, -OH, -NO2 groups in the aromatic ring. Preparation of aryl fluorides and iodides is not possible by direct halogenation. In chlorobenzene the cyano group cannot be introduced by nucleophilic substitution of chlorine in it. But we can easily obtain cyanobenzene from diazonium salts.
Preparation of substituted aromatic compounds is easily carried out by the replacement of diazo group with other groups which otherwise cannot be prepared by direct substitution to the benzene.
This article covers the reaction of diazonium salts by retention of diazo group and the significance of diazonium salt in the synthesis of aromatic compounds. For further query install Byju’s the learning app.