Test Index

Amines Part 1

Section: Chemistry

Question : 92 of 100

Marks: +1, -0

' A'

and

' B'

respectively are

[AIEEE 2010]

nitrobenzene and fluorobenzene
phenol and benzene
benzene diazonium chloride and fluorobenzene
nitrobenzene and chlorobenzene

Validate

Solution:

Primary aromatic amines react with nitrous acid to yield arene diazonium salts.

\underset{1^\circ\ \text{Aromatic amine}}{\mathrm{ArNH}_2 + \mathrm{NaNO}_2} + 2\,\mathrm{HX} \xrightarrow{\;\text{ cold }\;} \underset{\text{Arenediazonium salt}}{\mathrm{Ar}-\mathrm{N}=\mathrm{N}^{+}\mathrm{X}^{-}} + \mathrm{NaX} + 2\,\mathrm{H}_2\mathrm{O}

The diazonium group can be replaced by fluorine by treating the diazonium salt with fluoroboric acid

(\mathrm{HBF}_4)

. The precipitated diazonium fluoroborate is isolated, dried and heated until decomposition occurs to yield the aryl fluoride. This reaction is known as Balz-Schiemann reaction.

\mathrm{Ar}-\mathrm{N}_2^{+}\mathrm{X}^{-} \xrightarrow{\mathrm{HBF}_4} \mathrm{Ar}-\mathrm{N}_2^{+}\mathrm{BF}_4^{-}\downarrow \;\xrightarrow{\;\text{ Heat }\;} \mathrm{Ar}-\mathrm{F} + \mathrm{BF}_3 + \mathrm{N}_2

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