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Preparation and Properties of Aniline

A complete guide to the synthesis and reactions of Phenylamine.

By chemca Team • Updated Jan 2026

Aniline ($C_6H_5NH_2$) is the simplest aromatic amine. It is a key intermediate in the production of dyes, drugs, and polymers. Its chemistry is defined by the interaction between the amino group and the benzene ring.

1. Preparation Methods

A. Reduction of Nitrobenzene

The standard laboratory and industrial method involves reducing nitrobenzene with active metals in acidic medium.

$$ C_6H_5NO_2 + 6[H] \xrightarrow{Sn/HCl \text{ or } Fe/HCl} C_6H_5NH_2 + 2H_2O $$

Industrial Preference: Reduction with Scrap Iron ($Fe$) and $HCl$ is preferred because $FeCl_2$ formed hydrolyzes to release $HCl$. Thus, only a small amount of acid is required to initiate the reaction.

B. Hoffmann Bromamide Degradation

Benzamide is treated with Bromine and caustic potash to yield Aniline.

$$ C_6H_5CONH_2 + Br_2 + 4KOH \xrightarrow{\Delta} C_6H_5NH_2 + K_2CO_3 + 2KBr + 2H_2O $$

C. Ammonolysis of Chlorobenzene

Chlorobenzene reacts with ammonia in the presence of Cuprous Oxide ($Cu_2O$) at high temperature and pressure.

$$ 2C_6H_5Cl + 2NH_3 + Cu_2O \xrightarrow{473K, 60 atm} 2C_6H_5NH_2 + Cu_2Cl_2 + H_2O $$

2. Physical Properties

• State: Pure aniline is a colorless oily liquid. It turns brown on standing due to oxidation by air.
• Solubility: Sparingly soluble in water but soluble in organic solvents.
• Boiling Point: 457 K (Higher than comparable hydrocarbons due to intermolecular H-bonding).
• Toxic: It is toxic in nature.

3. Chemical Properties

A. Electrophilic Substitution

The $-NH_2$ group is strongly activating and ortho-para directing. To get mono-substituted products, the reactivity is controlled by Acetylation.

1. Bromination: Reaction with Bromine water gives a white precipitate of 2,4,6-Tribromoaniline.

$$ C_6H_5NH_2 + 3Br_2(aq) \rightarrow \underset{\text{White ppt}}{2,4,6\text{-Tribromoaniline}} + 3HBr $$

2. Nitration: Direct nitration yields a mixture of para (51%), meta (47%), and ortho (2%) products.

$Ph-NH_2 \xrightarrow{HNO_3/H_2SO_4} p\text{-Nitro} (51\%) + m\text{-Nitro} (47\%) + o\text{-Nitro} (2\%)$

Why Meta? In strongly acidic medium, aniline is protonated to form the Anilinium ion ($Ph-NH_3^+$), which is meta-directing.

3. Sulphonation: Heating with conc. $H_2SO_4$ yields Sulphanilic Acid, which exists as a Zwitterion.

$$ C_6H_5NH_2 + H_2SO_4 \xrightarrow{453K} \underset{\text{Sulphanilic Acid}}{p\text{-}H_2N-C_6H_4-SO_3H} \rightleftharpoons \underset{\text{Zwitterion}}{p\text{-}^+H_3N-C_6H_4-SO_3^-} $$

B. Diazotization

Reaction with Nitrous Acid ($NaNO_2 + HCl$) at low temperature (0-5°C) yields Benzene Diazonium Chloride, a vital intermediate.

$$ C_6H_5NH_2 + NaNO_2 + 2HCl \xrightarrow{273-278K} C_6H_5N_2^+Cl^- + NaCl + 2H_2O $$

C. Carbylamine Reaction

Specific test for primary amines. Aniline reacts with $CHCl_3$ and alc. KOH to form foul-smelling Phenyl Isocyanide.

$$ C_6H_5NH_2 + CHCl_3 + 3KOH \xrightarrow{\Delta} \underset{\text{Phenyl Isocyanide}}{C_6H_5NC} + 3KCl + 3H_2O $$

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