Name: Diazonium Salts for Aromatic Synthesis
Uploaded: 2019-07-19
Duration: 5 min 14 s
Description: Benzene diazonium salt is primarily used for the synthesis of substituted aromatic compounds. Are you curious to learn about the synthesis of such compounds?...

Question

How will you synthesise the following: Nitrobenzene from azobenzene?

Accepted Answer

The azobenzene can be converted into aniline as follows,

Aniline is dissolved in dilute hydrochloric acid and the solution is cooled to $0 ° - 5 ° C$ . Aqueous solution of sodium nitrite is added to the cooled solution in small portions with stirring. The temperature is maintained at $0 ° - 5 °$ . Addition of sodium nitrite solution is discontinued when a drop of the solution turns starch-iodide paper blue indicating the presence of slight excess of nitrous acid. Benzene diazonium chloride is formed in the solution. This reaction between a primary arylamine and nitrous acid in presence of a mineral acid to produce aryldiazonium salt is called diazotisation. Nitrous acid is unstable and it is always generated in situ from ${NaNO}_{2}$ and mineral acid like $HCl or H_{2} {SO}_{4}$ . The reaction is carried out at a low temperature $(0 ° - 5 ° C)$ , because both nitrous acid and diazonium salt would decompose at higher temperature.

$C_{6} H_{5} - {NH}_{2} \to_{HCl, 0 - 5 ° C}^{{NaNO}_{2}} C_{6} H_{5} {N_{2}}^{+} {Cl}^{-} + 2 H_{2} O .$

Nitro compounds are generally prepared by treating an arenediazonium fluoroborate with an aqueous solution of sodium nitrite in presence of copper powder.

The reaction is given below,

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How will you synthesise the following: Nitrobenzene from azobenzene?

Important Questions on Aryl Diazonium Salts

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