Organic Chemistry

Amines

Preparation of Amines — Complete Guide (English + Hindi)

Learn all practical methods to synthesize amines with reactions, tips, and exam-focused notes. Includes MCQs, True/False, Fill-ups, and FAQs.

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Table of Contents

1. Preparation of Amines (English)
2. Major Methods & Key Reactions
3. Summary Table
4. Exam Tips & Common Pitfalls
5. MCQ Practice + Answer Key
6. True/False + Explanations
7. Fill in the Blanks
8. FAQs (Schema Enabled)
9. एमाइन्स की तैयारी (Hindi)
10. Helpful Links

Preparation of Amines (English)

Amines are derivatives of ammonia (NH₃) where one or more hydrogens are replaced by alkyl/aryl groups. Depending on substitution, amines are primary (1°), secondary (2°), or tertiary (3°). This guide focuses on laboratory and industrial methods of preparation with clean, exam-oriented notes.

Major Methods & Key Reactions

1) Reduction of Nitro Compounds (Aromatic/Aliphatic → 1° Amines)

Reagents: Sn/HCl, Fe/HCl, or catalytic hydrogenation (H₂/Ni, Pd, Pt).

Example: Nitrobenzene → Aniline

C6H5NO2 --(Sn/HCl OR H2/Ni)--> C6H5NH2

Widely used industrially for aromatic amines.

2) Ammonolysis of Alkyl Halides (Mixture of 1°, 2°, 3° + Quaternary)

Reaction: R–X + NH₃ (alc., pressure) → R–NH₂, R₂NH, R₃N, [R₄N]X.

Control: Excess NH₃ favors 1°, but mixtures are common due to over-alkylation.

3) Gabriel Phthalimide Synthesis (Selective for 1° Amines)

Potassium phthalimide (nucleophile) reacts with R–X, followed by hydrolysis to give only primary amines (aliphatic).

Phthalimide-K+ + R–X → R–NH2 (after hydrolysis)

Note: Not suitable for aryl halides and cannot give 2°/3° amines.

4) Hofmann Bromamide Degradation (1 Carbon Less)

Reagents: Br₂/NaOH.

Reaction: R–CO–NH₂ → R–NH₂ + CO₃²⁻ (net loss of one carbon).

RCONH2 --(Br2/NaOH)--> RNH2

5) Reduction of Nitriles (R–C≡N → R–CH₂–NH₂)

Reagents: LiAlH₄ or H₂/Ni.

R–CN --(H2/Ni or LiAlH4)--> R–CH2–NH2

6) Reduction of Oximes (→ 1° Amines)

Oxime (R–CH=NOH) reduction with LiAlH₄/H₂ gives primary amines.

7) Curtius Rearrangement (Acyl Azides → 1° Amines, C−1)

Thermal decomposition of acyl azides leads to isocyanates → hydrolysis → 1° amines with one carbon less.

8) Schmidt Reaction (Carboxylic Acids + HN₃)

Carboxylic acid reacts with hydrazoic acid (conc. H₂SO₄) to give 1° amines (C−1). Handle with care (HN₃ is hazardous).

9) Reduction of Amides (Direct → Amines)

Amides reduced by LiAlH₄ yield corresponding amines (1°, 2°, or 3° depending on the amide).

Summary Table

Method	Starting Functional Group	Reagents	Main Product	Highlights
Reduction of Nitro	R–NO2	Sn/HCl, Fe/HCl, H2/Ni	R–NH2	Best for aromatic amines
Ammonolysis	R–X	NH3 (alc., pressure)	1°, 2°, 3°, quaternary	Mixtures; control challenging
Gabriel Synthesis	R–X	K phthalimide → hydrolysis	R–NH2 (only)	Selective for 1° (aliphatic)
Hofmann Degradation	R–CONH2	Br2/NaOH	R–NH2	Chain shortens by one carbon
Reduction of Nitriles	R–C≡N	LiAlH4, H2/Ni	R–CH2–NH2	Good for extending chain then reduce
Reduction of Oximes	R–CH=NOH	LiAlH4 / H2	R–CH2–NH2	Clean route to 1° amines
Curtius / Schmidt	Acyl azide / R–COOH	Heat / HN3, H2SO4	R–NH2	Carbon count decreases by one
Reduction of Amides	R–CONR’2	LiAlH4	Amines	Versatile; depends on amide type

Exam Tips & Common Pitfalls

• Gabriel gives only 1° aliphatic amines; not for aryl halides.
• Hofmann and Curtius/Schmidt all shorten the chain by one carbon.
• Ammonolysis tends to over-alkylate → mixtures; control with excess NH₃.
• Nitrile reduction is great after chain extension via nucleophilic substitution (e.g., CN⁻ then reduce).
• Safety: Hydrazoic acid and acyl azides are hazardous—follow proper protocols.

MCQ Practice (Reveal Answers)

1. Which method selectively yields only primary (aliphatic) amines?
   1. Ammonolysis of alkyl halides
   2. Gabriel phthalimide synthesis
   3. Reduction of nitro compounds
   4. Reduction of nitriles
   Answer(b). Gabriel synthesis gives only 1° aliphatic amines.
2. Hofmann bromamide degradation converts an amide into a primary amine with:
   1. Same carbon count
   2. One carbon more
   3. One carbon less
   4. Two carbons less
   Answer(c). The chain shortens by one carbon.
3. Reduction of nitriles (R–C≡N) typically affords:
   1. R–NH₂
   2. R–CH₂–NH₂
   3. R–CH₃
   4. R–CONH₂
   Answer(b). Nitrile → primary amine with one extra CH₂ between R and NH₂.
4. Ammonolysis of alkyl halides generally produces:
   1. Only primary amines
   2. Only secondary amines
   3. Only tertiary amines
   4. A mixture of 1°, 2°, 3° amines and quaternary salts
   Answer(d). Over-alkylation gives a mixture.
5. The best industrial route to aniline from nitrobenzene is:
   1. Gabriel synthesis
   2. Hofmann degradation
   3. Catalytic hydrogenation
   4. Curtius rearrangement
   Answer(c). H₂/Ni, Pd, or Pt.

True/False (With Explanations)

1. Gabriel synthesis works well for aryl halides. AnswerFalse. Aryl halides are unreactive under typical Gabriel conditions.
2. Schmidt reaction reduces carbon count by one. AnswerTrue. Carboxylic acid → amine with C−1.
3. Ammonolysis always yields a single product. AnswerFalse. Usually a mixture due to multiple alkylations.
4. Reduction of oximes can yield primary amines. AnswerTrue. Oxime → 1° amine on reduction.
5. Hofmann degradation increases the carbon chain length. AnswerFalse. It shortens the chain by one carbon.

Fill in the Blanks

1. In Gabriel synthesis, the nucleophile used is __________. AnswerPotassium phthalimide.
2. R–C≡N on reduction gives __________. AnswerR–CH₂–NH₂.
3. Hofmann degradation uses __________ and __________. AnswerBr₂ and NaOH.
4. Aromatic nitro compounds are reduced to amines using __________. AnswerSn/HCl, Fe/HCl, or catalytic hydrogenation.
5. Schmidt reaction employs hazardous reagent __________. AnswerHydrazoic acid (HN₃).

FAQs

Which method is best for only 1° amines?

Gabriel phthalimide synthesis (for aliphatic systems) is the most selective classroom method.

How to prepare aniline quickly?

Reduce nitrobenzene using H₂/Ni or Sn/HCl.

What is the carbon change in Hofmann vs Curtius?

Both decrease the carbon count by one (C−1).

Can ammonolysis give pure 1° amines?

Rarely. It typically gives mixtures due to over-alkylation.

Is hydrazoic acid safe?

No. It’s highly toxic and explosive—strict safety protocols are essential.

एमाइन्स की तैयारी (Hindi)

एमाइन्स अमोनिया (NH₃) के व्युत्पन्न हैं जिनमें हाइड्रोजन की जगह एल्किल/एरिल समूह आ जाते हैं। यहाँ प्रमुख तैयारी विधियाँ दी गई हैं:

1) नाइट्रो यौगिकों का अपचयन

अभिकारक: Sn/HCl, Fe/HCl, या H₂/Ni (उत्प्रेरक)। उदाहरण: नाइट्रोबेंजीन → एनिलीन।

2) एल्किल हैलाइड्स का अमोनोलाइसिस

R–X + NH₃ → 1°, 2°, 3° एमाइन तथा चतुर्धातुक अमोनियम लवण (आमतौर पर मिश्रण)।

3) गैब्रियल फ्थैलिमाइड विधि

केवल प्राथमिक (1°) अलिफैटिक एमाइन्स देती है; एरिल हैलाइड उपयुक्त नहीं।

4) हॉफमैन ब्रोमामाइड अपघटन

R–CONH₂ –(Br₂/NaOH)–> R–NH₂; शृंखला एक कार्बन से कम हो जाती है।

5) नाइट्राइल्स का अपचयन

R–C≡N –(LiAlH₄/H₂–Ni)–> R–CH₂–NH₂.

6) ऑक्सीम्स का अपचयन

R–CH=NOH → अपचयन द्वारा 1° एमाइन प्राप्त।

7) कर्टियस पुनर्विन्यास / श्मिट अभिक्रिया

एसिल एज़ाइड/कार्बोक्सिलिक अम्ल से 1° एमाइन; एक कार्बन कम हो जाता है।

8) अमाइड्स का प्रत्यक्ष अपचयन

LiAlH₄ से अमाइड्स → संबंधित एमाइन्स।

त्वरित सार

• Gabriel → केवल 1° (aliphatic) एमाइन।
• Hofmann/Curtius/Schmidt → कार्बन शृंखला एक से घटती है (C−1).
• Ammonolysis → सामान्यतः मिश्रण।

Helpful Links

• More on Organic Chemistry (CHEMASH)
• All posts tagged “Amines” (CHEMASH)
• Wikipedia: Amine (overview)

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