Question

Give the structures of A, B C in the following reactions:
(i) ${{\text{C}}_{\text{6}}}{{\text{H}}_{\text{5}}}{\text{N}}{{\text{O}}_2}\,\mathop \to \limits^{{\text{Sn + HCl}}} \,\,{\text{A}}\,\,\mathop \to \limits^{{\text{NaN}}{{\text{O}}_2}\, + {\text{HCl}}} \,{\text{B}}\,\mathop \to \limits^{{{\text{H}}_2}{\text{O}}} \,{\text{C}}$
(ii) ${\text{C}}{{\text{H}}_3}{\text{CN}}\,\mathop \to \limits^{{{\text{H}}_2}{\text{O/}}{{\text{H}}^ + }} {\text{A}}\mathop \to \limits^{{\text{N}}{{\text{H}}_3}{\text{/}}\Delta } \,{\text{B}}\mathop \to \limits^{{\text{B}}{{\text{r}}_2} + \,{\text{KOH}}} \,\,{\text{C}}$

Answer 1

Hint: Tin with hydrochloric acid is used for reduction and sodium nitrate with hydrochloric acid is used for the preparation of diazonium ion. Diazonium chloride gives electrophile which is used for nucleophilic addition. Hydrolysis of cyanide gives acid. The reaction of an acid with ammonia is used to generate amides.

Complete step by step answer:
(i) The reaction of nitrobenzene with tin in presence of hydrochloric is used for the reduction of a nitro group into an amine group. The formed product is known as aniline. The reaction of aniline with sodium nitrate and hydrochloric acid gives benzene diazonium chloride. On hydrolysis, the benzene diazonium chloride gives an electrophilic benzene ring by the removal of nitrogen gas. In this electrophilic ring, the hydroxyl group (nucleophile) attacks to give phenol.
The products are as follows:
${{\text{C}}_{\text{6}}}{{\text{H}}_{\text{5}}}{\text{N}}{{\text{O}}_2}\,\mathop \to \limits^{{\text{Sn + HCl}}} \,\,\mathop {{{\text{C}}_{\text{6}}}{{\text{H}}_{\text{5}}}{\text{N}}{{\text{H}}_2}}\limits_{{\text{aniline}}} \,\,\mathop \to \limits^{{\text{NaN}}{{\text{O}}_2}\, + {\text{HCl}}} \,\mathop {{{\text{C}}_{\text{6}}}{{\text{H}}_{\text{5}}}{\text{N}}_{\text{2}}^{\text{ + }}{\text{C}}{{\text{l}}^ - }\,\,}\limits_{{\text{diazonium}}\,\,{\text{ion}}} \mathop \to \limits^{{{\text{H}}_2}{\text{O}}} \,\mathop {{{\text{C}}_{\text{6}}}{{\text{H}}_{\text{5}}}{\text{OH}}}\limits_{{\text{phenol}}} \,$
So, product A is aniline, product B is benzene diazonium chloride and product C is phenol.
(ii) The complete hydrolysis of methyl cyanide gives acetic acid and the heating of acetic acid with ammonia gives the acetamide. Acetamide on reacting with bromine in presence of potassium hydroxide gives methyl amine.
The products are as follows:
${\text{C}}{{\text{H}}_3}{\text{CN}}\,\mathop \to \limits^{{{\text{H}}_2}{\text{O/}}{{\text{H}}^ + }} \mathop {{\text{C}}{{\text{H}}_3}{\text{COOH}}}\limits_{{\text{Acetic acid}}} \mathop \to \limits^{{\text{N}}{{\text{H}}_3}{\text{/}}\Delta } \,\mathop {{\text{C}}{{\text{H}}_3}{\text{CON}}{{\text{H}}_2}}\limits_{{\text{acetamide}}} \mathop \to \limits^{{\text{B}}{{\text{r}}_2} + \,{\text{KOH}}} \,\,\mathop {{\text{C}}{{\text{H}}_3}{\text{N}}{{\text{H}}_3}}\limits_{{\text{methylamine}}} \,\,\,\,\,$

So, product A is cyanobenzene, product B is benzoic acid and product C is benzamide.

Note: The ${\text{Sn+ }}\,{\text{HCl}}$ is reducing agents. The mixture of ${\text{NaN}}{{\text{O}}_{\text{2}}}\,{\text{ + }}\,{\text{HCl}}$ at high temperature is used for the preparation of diazonium chloride for electrophile generation. The reaction of amide with bromine in presence of potassium hydroxide to give primary amine is known as Hofmann degradation reaction.