Question

: Benzenediazonium chloride on reaction with aniline in a weakly acidic medium gives:
(A) Diphenyl ether
(B) p-Aminoazobenzene
(C) Chlorobenzene
(D) Benzene

Answer 1

When aniline reacts with HCl and ${\text{NaN}}{{\text{O}}_{\text{2}}}$ under a temperature of 274-278k it converts into Benzenediazonium salts, this reaction is also called diazotization. Diazonium salts are very unstable and are reacted very quickly with other reactants to yield a favorable product.

Complete step-by-step answer: We have understood the formation of Benzenediazonium chloride from the given hint, now let’s look at its chemical formula i.e. ${{\text{C}}_6}{{\text{H}}_5}\mathop {{{\text{N}}_2}}\limits^ + \mathop {{\text{Cl}}}\limits^ -$
So, according to the given condition we have ${{\text{C}}_6}{{\text{H}}_5}\mathop {{{\text{N}}_2}}\limits^ + \mathop {{\text{Cl}}}\limits^ -$ reacting with aniline, which is nothing but an aromatic amine with the chemical formula of ${{\text{C}}_6}{{\text{H}}_5}{\text{N}}{{\text{H}}_2}$ . And the reaction between the two yields a yellow coloured product, this reaction is also called a coupling reaction.
The reaction can be written as:
${{{\text{C}}_6}{{\text{H}}_5}\mathop {{{\text{N}}_2}}\limits^ + \mathop {{\text{Cl}}}\limits^ - } + {{\text{C}}_6}{{\text{H}}_5}{\text{N}}{{\text{H}}_2}\xrightarrow{{{{\text{H}}^ + }}}{{\text{C}}_6}{{\text{H}}_5}{\text{N}} \equiv {\text{N}}{{\text{C}}_6}{{\text{H}}_5}{\text{N}}{{\text{H}}_2} + {\text{C}}{{\text{l}}^ - } + {{\text{H}}_2}{\text{O}}$
The product formed is called p- Aminoazobenzene (yellow dye)

Additional information:
Benzene diazonium chloride is a versatile reagent and can be used to form a variety of products, the reactions of diazonium chloride is very useful for the conversion reactions.
The reaction of diazonium chloride with CuCl/HCl yields chlorobenzene and the reaction is called a Sandmeyer reaction.
Some physical properties of benzene diazonium chloride are:
i. It is a colourless crystalline solid.
ii.It is readily soluble in water and is stable in cold water.
iii.It decomposes easily in the dry state.

Hence, the correct answer is option (B) i.e. p- Aminoazobenzene

Note: Diazonium Chloride can also give the product benzene by reacting with hypophosphorous acid and chlorobenzene ( viz, Sandmeyer reaction), hence it is important to know about all the reagent which yields various products with Diazonium Chloride to solve these type of questions easily.