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Organic conversion

Aniline to p-hydroxyazobenzene

2 steps: diazotisation, then coupling reaction (azo dye)

Class 12, Chapter 9 Amines

  1. NH2
    AnilineC₆H₅NH₂Amine
  2. Step 1

    NaNO₂ + HCl

    273 to 278 K

    Diazotisation
    i

    Diazotisation: keep at 273 to 278 K or the salt decomposes. The acid generates HNO₂ in situ.

    N+NCl−
    Benzene diazonium chlorideC₆H₅N₂⁺Cl⁻Diazonium salt
  3. Step 2

    phenol, NaOH (OH⁻), 273 to 278 K

    Coupling reaction (azo dye)
    i

    Coupling at the para position of phenol in mildly alkaline medium gives the orange azo dye p-hydroxyazobenzene.

    HONN
    p-HydroxyazobenzeneC₆H₅N=NC₆H₄OHCompound

Exam answer

  1. Step 1: Aniline to benzene diazonium chloride: NaNO₂ + HCl, 273 to 278 K.
  2. Step 2: Benzene diazonium chloride to p-hydroxyazobenzene: phenol, NaOH (OH⁻), 273 to 278 K.
Why these reagents

Reagent and reason, step by step

  • Step 1: Aniline to benzene diazonium chloride: NaNO₂ + HCl, 273 to 278 K Diazotisation: keep at 273 to 278 K or the salt decomposes. The acid generates HNO₂ in situ.
  • Step 2: Benzene diazonium chloride to p-hydroxyazobenzene: phenol, NaOH (OH⁻), 273 to 278 K Coupling at the para position of phenol in mildly alkaline medium gives the orange azo dye p-hydroxyazobenzene.
Questions

Aniline to p-hydroxyazobenzene: quick answers

How many steps does it take to convert aniline to p-hydroxyazobenzene?

2 steps: Aniline, then benzene diazonium chloride, then p-hydroxyazobenzene.

Which named reaction is used to convert aniline to p-hydroxyazobenzene?

Diazotisation and Coupling reaction (azo dye). A primary aromatic amine reacts with nitrous acid (NaNO2 and HCl) at 273 to 278 K to give a diazonium salt.

What is the reagent for step 1 of aniline to p-hydroxyazobenzene?

Aniline to benzene diazonium chloride: NaNO₂ + HCl, 273 to 278 K. Diazotisation: keep at 273 to 278 K or the salt decomposes. The acid generates HNO₂ in situ.

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