(i) Nitration of aniline is accompanied by oxidation. But a mixture of cone. HNO₃ and cone. H₂SO₄ gives m-nitroaniline also. Nitric acid is a strong acid. It protonates aniline forming anilinium ion C₆H₅NH₃⁺ because of positive charge on nitrogen it is meta directing.

p-nitro aniline is prepared in the following three stages

(ii) Aniline reacts with acetyl chloride and acetic anhydride to form corresponding amides called anilides.
\({ C }_{ 6 }H_{ 5 }{ NH }_{ 2 }+\underset { Acetylchloride }{ ClCO{ CH }_{ 3 } } \rightarrow \underset { Acetanilide }{ { C }_{ 6 }{ H }_{ 5 }NHCO{ CH }_{ 3 } } +HCl\)
\({ C }_{ 6 }H_{ 5 }{ NH }_{ 2 }+\underset { Aceticanhydride }{ { CH }_{ 3 }COOCO{ CH }_{ 3 } } \rightarrow \underset { Acetanilide }{ { C }_{ 6 }{ H }_{ 5 }NHCO{ CH }_{ 3 } } +{ CH }_{ 3 }COOH\)

(i) Primary amine react with nitrous acid to form alcohols and nitrogen gas
\(\underset { primary \ amine }{ { CH }_{ 3 }NH_{ 2 } } \rightarrow \underset { unstable }{ { [{ CH } }_{ 3 }-N=N-OH] } \rightarrow { CH }_{ 3 }OH+{ N }_{ 2 }\)
Aliphatic diazonium compound is unstable because of absence of resonance stabilisation.
(ii) Secondary amines react with nitrous acid to form N-nitroso amines which are water insoluble yellow oils.
\(\underset { Secondary \ amine }{ { { (CH }_{ 3 } })_{ 2 }NH } +HO-N=O\rightarrow \underset { N-nitroso \ dimethy \ amine-yellow \ oil\\ (insolube \ in \ water) }{ { (CH }_{ 3 })_{ 2 }N-N=O } \)
(iii) Tertiary amine react with nitrous acid to form trialkyl ammonium nitrite salts which are soluble in water
\(\underset { Tertiary \ amine }{ { (CH }_{ 3 })_{ 2 }N } +HONO\rightarrow \underset { trimethyl \ ammonium \ nitrite\\ (salt \ soluble \ in \ water) }{ { { (CH }_{ 3 }) }_{ 3 }{ NH }^{ + }{ NO }_{ 2 }^{ - } } \)

i) Nitrobenzene ⇾ Nitrosobenzene
When nitrobenzene is treated with glucose and NaOH (alkaline medium) Nitrosobenzene is formed.
\({ C }_{ 6 }{ H }_{ 5 }N{ O }_{ 2 }\rightarrow \underset { Nitrosobenzene }{ { C }_{ 6 }{ H }_{ 5 }NO+{ H }_{ 2 }O } \)
ii) Nitrobenzene ⇾ Azoxybenzene
When nitrobenzene is subjected to reduction with glucose and NaOH forms the intermediate products nitrosobenzene and phenyl hydroxyl amine. These undergo bimolecular condensation reaction to give azoxy benzene.
\({ C }_{ 6 }{ H }_{ 5 }N{ O }_{ 2 }\underrightarrow { Glucose+NaOH } \underset { Nitrosobenzene }{ { C }_{ 6 }{ H }_{ 5 }NO+{ H }_{ 2 }O } \xrightarrow [ { H }_{ 2 }O ]{ \triangle } \underset { Azoxy\quad benzene }{ { C }_{ 6 }{ H }_{ 5 }-N=N{ C }_{ 6 }{ H }_{ 5 } } \)
iii) Nitrobenzene ⇾ Hydrazobenzene
When nitrobenzene is subjected to alkaline reduction in the presence of Zn+NaOH, hydrozo benzene is formed.
\({ C }_{ 6 }{ H }_{ 5 }N{ O }_{ 2 }\underrightarrow { Zn/NaOH } \underset { Nitrosobenzene }{ { C }_{ 6 }{ H }_{ 5 }NH+{ NHC }_{ 6 }{ H }_{ 5 }} \)

(i) CH₃CN (Methyl cyanide) on reduction gives CH₃CH₂NH₂ (ethylamine) because addition of hydrogen takes place at ≡ CN
\({ CH }_{ 2 }-C\equiv N\xrightarrow [ 4H ]{ { LiAH }_{ 4 } } { \underset { Ethylamine\\ (Primary\quad amine) }{ { CH }_{ 3 }-{ CH }_{ 2 }{ NH }_{ 2 } } }\)
Whereas CH₃NC (Methyl isocyanide) on reduction with LiAlH₄ gives secondary amine
\({ CH }_{ 3 }-\underset { \overset { | }{ H } }{ N } -{ CH }_{ 3 }\)

In methyl cyanide, -CN group is attached to alkyl group and by reduction it gives a primary amine wherease in methyl isocyanide -NC group is attached to alkyl group and by reduction it gives a secondary amine.
(ii) (CH₃)₂ NH (Secondary amine) requires 2 moles of CH₃I to give a quaternary salt (crystalline product) whereas (CH₃)₂N (tertiary amine) require only one mole of CH₃I to give the same quaternary salt. It is due to the number of alkyl groups present in amines.
\(\underset { Secondary \ anmine }{ { ( }{ CH }_{ 3 })_{ 2 }-NH+{ 2CH }_{ 3 }I } \rightarrow { { [(CH }_{ 3 })_{ 4 }N] }^{ + }\underset { Tetramethy\\ ammonium \ iodide }{ { I }^{ - } } \)
(iii) Nitration of aniline with cone. HNO₃ results in the formation of m-nitro aniline because nitric acid is a strong acid. It protonates aniline forming anilinium ion C₆H₅NH3+ because of positive charge on nitrogen, it is meta directive and -NO₂ group is substituted at meta position.

(iv) p-Toluidine contains a methyl group which has +I effect (electron withdrawing group and due to this, p-toluidine is a stronger base than p-nitro aniline in which the nitro group is less reactive and it deactivate the benzene rin make it a less basic

i) (CH₃)₂ NH is stronger base than NH₃:
(a) (CH₃)₂NH (Secondary amine) is a stronger base than NH₃ (ammonia).
(b) In dimethylamine, the methyl group with +1 effects tends to Increase the electron density on the nitrogen atom.
(c) As a result, the electron releasing tendency or basic strength of amine increases.
ii) CH₃CH₂NH₂ is more basic than CH₃CONH₂:
(a) Resonance and inductive effect possible in acetamide involving the non bonding pair of electrons on the nitrogen atom.
(b) Another important factor is that amides containing a powerful electron is not readily available for donation and it is less basic.
(c) Thus ethylamine is more basic than acetamide.
iii) Aniline is less basic than Ethyl amine:
(a) The lone pair of electrons on the nitrogen atom of aniline is involved in resonance and is not easily available for donation to protons.
(b) The positive charge on nitrogen makes protonation difficult. Thus aniline is less basic than ethylamine.
vi) When aniline is heated with fuming sulphuric acid, p-amino benzene sulphonic acid is formed.

Aniline does not give o-amino benzene sulphonic acid because it is sterically less favoured.