Chapter 16 – Amines | Nepal eNotes

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CHEMISTRY • CHAPTER 16

Aromatic Amine

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Aromatic amine

Aniline

(1°)

N−phenylaniline

(2°)

N,N,−di−phenylamine

(3°)

N−methylaniline

Preparation

1) From Nitrobenzene

i) Catalytic reduction

Nitrobenzene + 6[H] Ni / Pt / Pd→ Aniline + 2H₂O

ii) Acidic reduction

Nitrobenzene + 6[H] Sn / HCl→ Aniline + 2H₂O

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Properties

i) Aniline are less basic than Aliphatic amine and ammonia

R−NH₂ > NH₃ > Ar−NH₂

Basic character

because available of lone pair of electron in nitrogen atom is decreases due to the resonance.

ii) Rxn with HCl or H₂SO₄

Aniline + HCl → [C₆H₅NH₃]⁺Cl⁻

Anilinium chloride

Aniline + H₂SO₄ → [C₆H₅NH₃]₂SO₄

Anilinium sulphate

iii) Alkylation (Rxn with alkyl halide)

Aniline CH₃Cl / −HCl→ N−methylaniline CH₃Cl / −HCl→ N,N−dimethyl aniline

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N,N−dimethyl aniline + CH₃Cl → [C₆H₅N(CH₃)₃]⁺Cl⁻

Trimethylanilinium chloride

iii) Acylation

Aniline + CH₃COCl → C₆H₅NHCOCH₃ + HCl

acid halide (acetic chloride) → N−phenylethanamide (acetanilide)

iv) Carbylamine rxn

C₆H₅NH₂ + CHCl₃ + 3KOH alc→ C₆H₅NC + 3KCl + 3H₂O

phenyl isocyanide

v) Coupling rxn

Benzenediazonium chloride + Aniline → p−aminoazobenzene + HCl

orange red dye

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vi) Diazotization

C₆H₅NH₂ + HNO₂ NaNO₂ + HCl, 0−5°C→ C₆H₅N₂Cl + 2H₂O

B.D.C. (Benzenediazonium chloride)

vii) Electrophilic substitution rxn

Note: ortho para director

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viii) Halogenation

Aniline + 3Br₂ aq→ 2,4,6−tribromoaniline + 3HBr

white ppt

ix) Sulphonation

Aniline + HO−SO₃H → p−aminobenzene sulphonic acid + H₂O

x) Nitration

Direct nitration of aniline is not carried out because −NH₂ group is good reducing agent and conc HNO₃ is strong oxidizing agent which produce black mass. Therefore during nitration at first amino group (−NH₂) is protected by acylation and then followed by nitration.

Aniline + CH₃COCl → Acetanilide + HCl

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Acetanilide + HNO₃ conc H₂SO₄, Δ→ o−nitroacetanilide + p−nitroacetanilide

o−nitroacetanilide + p−nitroacetanilide H₂O / H⁺→ o−nitroaniline + p−nitroaniline

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