Nitrogen Containing Compounds

Introduction

Important nitrogen containing organic compounds are alkyl nitrites (RONO), nitro-alkanes (RNO2), aromatic nitro compounds (ArNO2), alkyl cyanides (RCN), alkyl iso cyanides (RNC), amines (–NH2), aryl diazonium salts (ArN2Cl), amides (–CONH2) and oximes (>C = N OH).

Tautomerism in Nitrous Acid

H–O–N=O

⇌

H–O=N–O

Leads to alkyl nitrites and nitroalkanes.

Alkyl Nitrites & Nitroalkanes

Alkyl Nitrites (RONO)

Preparation (Ethyl Nitrite)

C2H5OH + HNO2 → C2H5ONO + H2O

C2H5I + KONO → C2H5ONO + KI

2C2H5OH + N2O3 → 2C2H5ONO + H2O

Physical Properties

Gas at room temp, liquifies on cooling, b.p. 17°C, apple smell, insoluble in water, soluble in alcohol/ether.

Chemical Properties

C2H5ONO + H2O → C2H5OH + HNO2 (Hydrolysis)

C2H5ONO + 6H → C2H5OH + NH3 + 2H2O (Reduction Sn/HCl)

Uses

Treatment of asthma, heart diseases; diuretic; source of nitrous acid.

Nitroalkanes (RNO2)

Classification

Primary (RCH2NO2), Secondary (R2CHNO2), Tertiary (R3CNO2)

Preparation

RX + AgNO2 → RNO2 + AgX

RH + HNO3 → RNO2 + H2O (Vapour phase)

RCH2CH2Cl + NaNO2 → RCH2CH2NO2

R3CNH2 + KMnO4 → R3CNO2

Physical Properties

Colourless pleasant liquids, sparingly soluble in water, soluble in organic solvents, high b.p. due to polarity.

Chemical Properties

RNO2 + 6H → RNH2 + 2H2O (Reduction)

RCH2NO2 + HOH → RCOOH + NH2OH (Hydrolysis 1°)

R2CHNO2 + HOH → R2C=O + HNO2 (Hydrolysis 2°)

RNO2 + HNO2 → Nitrolic acid or Pseudonitrol

RNO2 + Cl2 → Halogenation at α-position

Uses

Solvents for polar substances, explosives, preparation of amines, hydroxylamines, chloropicrin.

Test	Ethyl Nitrite (C2H5ONO)	Nitro Ethane (C2H5NO2)
Boiling Point	17°C	115°C
Reduction (Sn/HCl)	C2H5OH + NH2OH	C2H5NH2
NaOH	Hydrolysed to C2H5OH	Forms salt
HNO2	No action	Forms nitrolic acid

Aromatic Nitro Compounds

Preparation

ArH + HNO3/H2SO4 → ArNO2

Indirect from amines via diazonium salts.

Physical Properties

Insoluble in water, soluble in organic solvents, pale yellow liquids/solids with smells.

Chemical Properties

ArNO2 + 6H → ArNH2 (Reduction)

Electrophilic substitution at m-position, nucleophilic substitution if o/p-NO2.

Uses

Solvents, explosives, amino compounds, shoe polish, soaps.

Cyanides and Isocyanides

Alkyl Cyanides (RCN)

Preparation

RX + KCN → RCN

RCOOH + NH3 → RCONH2 → RCN (Dehydration)

Physical Properties

Neutral, pleasant odour, liquids/solids, soluble in water/organic solvents, poisonous.

Chemical Properties

RCN + 2H2O → RCOOH + NH3 (Hydrolysis)

RCN + 4H → RCH2NH2 (Reduction)

RCN + R'MgX → RCOR' (Grignard)

Uses

Intermediates for acids, amides, esters, amines.

Alkyl Isocyanides (RNC)

Preparation

RX + AgCN → RNC

RNH2 + CHCl3 + 3KOH → RNC (Carbylamine)

Physical Properties

Colourless unpleasant liquids, insoluble in water, soluble in organics, more poisonous than cyanides.

Chemical Properties

RNC + 2H2O → RNH2 + HCOOH (Hydrolysis)

RNC + 4H → RNHCH3 (Reduction)

Uses

Detection of leakage, test for primary amines.

Amines

Classification & Structure

Derivatives of NH3: Primary (RNH2), Secondary (R2NH), Tertiary (R3N), Quaternary (R4N+)

Pyramidal shape, sp3 hybridized N.

Preparation of Amines

Mixture of Amines

RX + NH3 → RNH2 + R2NH + R3N

ROH + NH3 → RNH2 + R2NH + R3N (Al2O3)

Primary Amines

RNO2 + 6H → RNH2

RCN + 4H → RCH2NH2

RCONH2 + Br2 + KOH → RNH2 (Hofmann)

Phthalimide + RX → RNH2 (Gabriel)

Secondary Amines

RNH2 + RX → R2NH

RNC + 4H → RNHCH3

p-Nitroso-dialkylaniline + NaOH → R2NH

Tertiary Amines

RNH2 + 2RX → R3N

R2NH + RX → R3N

Separation of Amines

Fractional distillation, Hofmann's method (diethyl oxalate), Hinsberg's method (benzenesulfonyl chloride).

Physical Properties

Gases/low b.p. liquids with fishy odour, H-bonding, soluble in water/organics, b.p. order: 2° > 1° > 3°.

Chemical Properties

Basicity Order

Aliphatic: 2° > 1° > 3° > NH3 (gas phase: 3° > 2° > 1° > NH3)

Aromatic: Weaker than aliphatic due to resonance; substituents affect: +I increase, -I decrease.

Salt Formation

RNH2 + HCl → RNH3+Cl–

Alkylation

RNH2 + RX → R2NH → R3N → R4N+X–

Acylation

RNH2 + CH3COCl → RNHCOCH3

Carbylamine

RNH2 + CHCl3 + 3KOH → RNC

Nitrous Acid

1°: ROH + N2; 2°: R2N–NO; 3°: Salt

Oxidation

1°: Aldehydes/Ketones; 2°: Hydroxylamines; 3°: Amine oxides

Ring Substitution (Aromatic)

Activating, o/p directing; protect NH2 for control.

Test	1° Amine	2° Amine	3° Amine
Carbylamine	Bad smell RNC	No	No
Mustard Oil	Mustard smell	No	No
HNO2	N2 gas	Nitrosoamine	Salt
Acetyl Chloride	Acetyl deriv	Acetyl deriv	No
Hinsberg	Soluble sulfonamide	Insoluble	No
CH3I	3 moles	2 moles	1 mole

Diazonium Salts (ArN2+X–)

Preparation

ArNH2 + NaNO2 + HCl → ArN2+Cl– (0-5°C)

Physical Properties

Colourless crystalline, water soluble, unstable, explosive when dry.

Chemical Properties

Substitution

ArN2+Cl– + H2O → ArOH + N2 (Warm)

ArN2+Cl– + H3PO2 → ArH + N2

ArN2+Cl– + CuCl → ArCl + N2 (Sandmeyer)

ArN2+Cl– + KI → ArI + N2

ArN2+BF4– → ArF + N2 + BF3 (Balz-Schiemann)

ArN2+Cl– + CuCN → ArCN + N2

ArN2+Cl– + NaNO2/Cu → ArNO2 + N2

ArN2+Cl– + KSH → ArSH + N2

Coupling Reactions

ArN2+Cl– + C6H5OH → ArN=NC6H4OH (p-Hydroxyazobenzene)

ArN2+Cl– + C6H5NH2 → ArN=NC6H4NH2

Uses: Azo dyes, organic synthesis, halogen arenes.

JEE Main Weightage

Typically 3-4 questions from Nitrogen Compounds. Focus on amine preparation/separation, reactions with HNO2, diazonium reactions, basicity order.

Weightage High (3-4 Qs)