CHEMCA
EXAM MASTER REVIEW SHEET
Organic Compounds Containing Nitrogen: Amines
1. Structure & Basicity Order
Amines are derivatives of ammonia where H atoms are replaced by alkyl/aryl groups. Nitrogen is $sp^3$ hybridized with a pyramidal shape.
Purely governed by $+I$ effect of alkyl groups.
$3^\circ > 2^\circ > 1^\circ > NH_3$
Governed by $+I$ effect, Solvation effect, and Steric hindrance.
- • If $R = -CH_3$: $2^\circ > 1^\circ > 3^\circ > NH_3$ (213)
- • If $R = -C_2H_5$: $2^\circ > 3^\circ > 1^\circ > NH_3$ (231)
2. Methods of Preparation
Gabriel Phthalimide Synthesis
Phthalimide $\xrightarrow{KOH}$ Pot. Phthalimide $\xrightarrow{RX}$ N-Alkylphthalimide $\xrightarrow{NaOH}$ Primary ($1^\circ$) Aliphatic Amine.
• Note: Aromatic $1^\circ$ amines (Aniline) cannot be prepared by this method.
Reduction Methods
• Nitriles: $R-CN \xrightarrow{H_2/Ni \text{ or } LiAlH_4} R-CH_2NH_2$.
• Amides: $R-CONH_2 \xrightarrow{LiAlH_4/H_2O} R-CH_2NH_2$.
• Nitro: $Ar-NO_2 \xrightarrow{Fe/HCl \text{ or } Sn/HCl} Ar-NH_2$.
3. Key Chemical Reactions
| Reaction | Reagents | Product / Note |
|---|---|---|
| Acylation | $RCOCl$ or $(RCO)_2O$ | Amides. Used to "protect" $-NH_2$ group. |
| Carbylamine Reaction | $CHCl_3 + alc. KOH$ | Isocyanide ($R-NC$) - Foul smell. ($1^\circ$ only) |
| Reaction with $HNO_2$ | $NaNO_2 + HCl$ (0-5°C) | Aliphatic $\rightarrow$ Alcohol + $N_2$; Aromatic $\rightarrow$ BDC. |
| Electrophilic Subst. | $Br_2 / H_2O$ | 2,4,6-Tribromoaniline (White ppt). |
4. Hoffmann Bromamide Degradation
An amide is treated with bromine in an aqueous or ethanolic solution of sodium hydroxide to give an amine with one carbon atom less than that present in the amide.
Crucial for descending a homologous series.
5. Hinsberg Test & Identification
Hinsberg Reagent ($C_6H_5SO_2Cl$)
- • $1^\circ$ Amine: Soluble in alkali after reaction.
- • $2^\circ$ Amine: Insoluble in alkali after reaction.
- • $3^\circ$ Amine: Does not react at all.
Azo Dye Test
Aromatic $1^\circ$ amines (like Aniline) react with $HNO_2$ (0-5°C) followed by 2-Naphthol.
Observation: Brilliant Orange/Red Dye.
*Distinguishes Aniline from aliphatic amines.*
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