Question

Write the balanced chemical equation for Balz- Schiemann reaction and Sandmeyer reaction.

Answer 1

Hint: As we know that, the balanced chemical equation follows the law of conservation of mass. Balz- Sehiemann reaction is the reaction of aniline and proceeds with the same intermediate formation as the Sandmeyer reaction but Balz- Schiemann reaction is more specific towards product and Sandmeyer reaction is not specific for one.

Complete Step by step answer: Balz- Schiemann reaction is a reaction in which we get fluorobenzene from primary amine by nucleophilic substitution reaction. In this reaction, one mole of amine reacts with nitrous acid and gives diazonium salt as an intermediate. This salt is formed because the aniline is a Lewis base and nitrous acid is an acid which forms salt by eliminating water molecules. This intermediate again reacts with fluoroboric acid and gives fluorobenzene by eliminating nitrogen gas along with tri-flouro-borane hydrochloric acid.
\[{{\rm{C}}_{\rm{6}}}{{\rm{H}}_{\rm{7}}}{\rm{N}}\,{\rm{ + }}\,{\rm{HN}}{{\rm{O}}_{\rm{2}}}\,{\rm{ + }}\,{\rm{HCl}}\, \to \,{{\rm{C}}_{\rm{6}}}{{\rm{H}}_{\rm{5}}}{{\rm{N}}^{\rm{ + }}}_{\rm{2}}{\rm{C}}{{\rm{l}}^{\rm{ - }}}\,{\rm{ + }}\,{\rm{2}}{{\rm{H}}_{\rm{2}}}{\rm{O}} \xrightarrow[hv]{HBF4} {{\rm{C}}_{\rm{6}}}{{\rm{H}}_{\rm{5}}}{\rm{F + }}{{\rm{N}}_{\rm{2}}}\,{\rm{ + }}\,{\rm{B}}{{\rm{F}}_{\rm{3}}}\,{\rm{ + }}\,{\rm{HCl}}\]
From diazonium salt we can also form any halobenzene in the presence of copper halide. This reaction is also formed by nucleophilic substitution reactions. This is known as the Sandmeyer reaction.
\[{{\rm{C}}_{\rm{6}}}{{\rm{H}}_{\rm{5}}}{{\rm{N}}^{\rm{ + }}}_{\rm{2}}{\rm{C}}{{\rm{l}}^{\rm{ - }}} \xrightarrow[CuX ]{HX}{{\rm{C}}_{\rm{6}}}{{\rm{H}}_{\rm{5}}}{\rm{X}}\,{\rm{ + }}\,{{\rm{N}}_{\rm{2}}}\,{\rm{ + }}\,{\rm{HCl}}\,\,\,\,\,\,\,\,\,\left( {\,{\rm{X}}\,{\rm{ = }}\,{\rm{Cl,}}\,\,{\rm{Br}}\,\,{\rm{or}}\,\,{\rm{I}}\,} \right)\,\]

Note: As we can see that, the above two reactions are formed by the diazonium salt which is formed by the primary amines.
The above reactions are also used to distinguish between primary, secondary and tertiary amines.
Only primary amines form diazonium salt. Secondary amines undergo diazotization, the (nitrosonium ion) directly bonded with amine.
If the tertiary amines undergo diazotization, the electrophile bonds at para position because the para position of tertiary amine is rich in electron density. Ortho positions of tertiary amines are crowded.