Lesson Plan: Amines

Organic Chemistry (Class 12)

Amines

Derivatives of Ammonia. This chapter is famous for its "Basicity Anomalies" (Methyl vs Ethyl amines in water). It also covers Diazonium Salts, which are crucial intermediates for synthesizing Azo dyes and other aromatic compounds.

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⚠️ Prerequisites

Inductive Effect: Impact of +I groups on electron density on Nitrogen.
Solvation: Hydrogen bonding with water molecules.
Reduction: $LiAlH_4$ reduction of Nitriles and Amides.

🧠 Study Approach

Basicity is Key: Understand the tug-of-war between Inductive Effect (favors $3^\circ$), Steric Hindrance (favors $1^\circ$), and Solvation (favors $1^\circ$). This explains the weird basicity orders in aqueous solutions.

Study Sequence

1. Structure & Nomenclature

$1^\circ (-NH_2)$, $2^\circ (>NH)$, $3^\circ (>N-)$ classification. Pyramidal shape of Nitrogen (sp3 hybridized with 1 lone pair). IUPAC naming (Alkanamine).

2. Preparation of Amines

Gabriel Phthalimide: Only for $1^\circ$ Aliphatic amines (Ar-X doesn't react).
Hoffmann Bromamide Degradation: Amide $\to$ Amine with ONE LESS CARBON. ($RCONH_2 \to RNH_2$).
Reduction of Nitro, Nitriles, and Amides.

3. Physical Properties

Boiling Point: Alcohol > $1^\circ$ Amine > $2^\circ$ Amine > $3^\circ$ Amine (No H-bond).
Solubility in water decreases as molar mass increases.

4. Basicity of Amines (CRITICAL)

Gas Phase: $3^\circ > 2^\circ > 1^\circ > NH_3$ (Pure +I effect).
Aqueous Phase: Interplay of Steric + Solvation + Inductive.
Methyl: $2^\circ > 1^\circ > 3^\circ > NH_3$. Ethyl: $2^\circ > 3^\circ > 1^\circ > NH_3$.
Arylamines: Less basic than alkylamines (Lone pair delocalized).

5. Chemical Reactions & Tests

Carbylamine Reaction: Test for $1^\circ$ amines only (Foul smell of Isocyanide).
Reaction with $HNO_2$: $1^\circ$ Aliphatic $\to$ Alcohol + $N_2$. Aromatic $\to$ Diazonium salt.
Hinsberg Reagent: Distinguishes $1^\circ, 2^\circ, 3^\circ$ amines based on solubility in Alkali.

6. Reactions of Aniline

Electrophilic Substitution: $-NH_2$ is strongly activating (o,p-directing).
Protection: Acetylation is needed before Nitration/Bromination to prevent polysubstitution and oxidation.

7. Diazonium Salts ($ArN_2^+X^-$)

Sandmeyer / Gattermann: Replacement by $Cl, Br, CN$.
Azo Coupling: Reaction with Phenol (Orange Dye) and Aniline (Yellow Dye). Retains $N=N$ bond.

🎯 How to Practice

Basicity Numbers: Memorize "213" for Methyl amines ($2^\circ > 1^\circ > 3^\circ$) and "231" for Ethyl amines ($2^\circ > 3^\circ > 1^\circ$). This is the most asked MCQs.

Step Up vs Step Down: Practice conversion:
Step Up: $R-X \xrightarrow{KCN} R-CN \xrightarrow{Red} R-CH_2-NH_2$.
Step Down: $R-CONH_2 \xrightarrow{Br_2/KOH} R-NH_2$.

Distinction Table: Create a table for Carbylamine, Nitrous Acid, and Hinsberg tests. Note observations for $1^\circ, 2^\circ, 3^\circ$ amines.

📝 Quick Revision Notes

Basicity in Aqueous

Methyl ($R=CH_3$): $2^\circ > 1^\circ > 3^\circ > NH_3$

Ethyl ($R=C_2H_5$): $2^\circ > 3^\circ > 1^\circ > NH_3$

Hinsberg Test (Benzene sulphonyl chloride)

$1^\circ$: Soluble in Alkali.
$2^\circ$: Insoluble in Alkali.
$3^\circ$: No Reaction.

Hoffmann Bromamide

$R-CONH_2 + Br_2 + 4KOH \to R-NH_2 + K_2CO_3$
(Product has 1 less carbon)

Azo Dyes

Phenol Coupling $\to$ Orange Dye (Basic medium)
Aniline Coupling $\to$ Yellow Dye (Acidic medium)

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