DIAZONIUM SALT

Diazonium salt is a very vital compound (intermediate) in the chemical industry, and most importantly the dyes industry. it can serve many purposes such as; production of dyes, phenols, iodobenzene, bromobenzene, fluorobenzene etc. diazonium compound share a common functional group as shown below.       R-N₂⁺X

DIAZONIUM SALT

                                              ^-                  
                                                                                   

  where R is an alkyl (i.e. aliphatic substituted diazonium compound) and an aryl (i.e. aromatic substituted diazonium compound). On this page, we are going to discuss basically on the production of aromatic diazonium compound from basic raw material.


NOTE: The aromatic substituted diazonium compound is a very important intermediate in the organic synthesis of azo dyes and also other solvents.

                         
  PREPARATION STEPS

• The first step involve the preparation of benzene from ethyne (obtained from crude oil) by polymerization reaction in a red hot tube as shown below;

Polymerization of ethyne in hot Red tube

NOTE: For this reaction three molecules of ethyne is used. Benzene can also be obtained from destructive distillation of coal.

• secondly, the benzene obtained then undergoes nitration reaction with concentrated nitric acid in the presence of concentrated sulphuric acid which helps with the formation of the electrophile (NO₂) as shown below. in this reaction, nitro-benzene is formed.

Formation of electrophile  (NO₂)

Reaction of electrophile with benzene

Overall Reaction of benzene and nitric acid and sulphuric acid

NOTE: this reaction is possible because electrons are available below and above the ring of benzene. The reaction above is known as electrophilic substitution reaction.

• thirdly, the nitro-benzene formed above is then reduced to amino-benzene (aniline) by reacting with tin (Sn) in the presence of hydrochloric acid (HCL) as shown below. this method is one of the basic method used in the production of anines.

reduction reaction of nitro-benzene and tin in hydrochloric acid

• lastly, the amino-benzene is then reacted with nitrous acid in the presence of hydrocloric acid (HONO/HCL) or NaNO₂/HCL to give the diazonium salt as shown by the reaction below;

NOTE: It is very important to note that tertiary aliphatic amines have no replaceable hydrogen and so remain as salt in solution when reacted with nitrous acid (HONO) while tertiary aromatic amines undergo ring substitution to form green or blue-green p-nitroso derivative.

Therefore tertiary aliphatic amines cannot be used to synthesize diazonium salt.

the basic reactions of diazonium salt will be discussed in our next chapter for proper understanding of the usefulness of diazonium salt