# Preparation of amines

> CIE A-Level Chemistry · 9701
> Source: https://www.owlsprep.com/study/cie-9701-u23-preparation-of-amines/

This module covers the main laboratory and industrial preparation methods for both aliphatic and aromatic amines, including reaction conditions, starting materials, and common pitfalls tested in CIE A-Level 9701 exams.

**Prerequisites:** [Nucleophilic substitution reactions](https://www.owlsprep.com/study/cie-9701-u18-nucleophilic-substitution/); [Redox reactions of organic compounds](https://www.owlsprep.com/study/cie-9701-u20-organic-redox/)

## Learning objectives

- Describe the main routes for preparing aliphatic and aromatic amines
- State correct reaction conditions for each preparation method
- Identify suitable starting materials for a target amine product

## Preparation of Aliphatic Amines: Nitrile Reduction

**Nitrile Reduction** — Reduction of the nitrile group ($-C\equiv N$) to form a primary amine, adding 4 hydrogen atoms across the triple bond

*Example:* Propanenitrile reduces to propan-1-amine

Reduction of nitriles is the preferred method for producing pure primary aliphatic amines, with one more carbon atom than the starting halogenoalkane. Two reagent combinations are accepted in CIE exams: 1) H₂ gas with a nickel catalyst, heated under pressure, or 2) LiAlH₄ in dry ether, followed by dilute acid hydrolysis.

**Worked example:** Starting from bromoethane, outline the synthesis of propan-1-amine via nitrile reduction, including all reagents and conditions.

1. Step 1: First, bromoethane reacts with KCN in ethanol, heated under reflux, via nucleophilic substitution to form propanenitrile:
2. $$CH_3CH_2Br + KCN \rightarrow CH_3CH_2CN + KBr$$
3. Step 2: Propanenitrile is then reduced to propan-1-amine:
4. $$CH_3CH_2CN + 4[H] \rightarrow CH_3CH_2CH_2NH_2$$
5. Step 3: If using H₂/Ni, conditions are ~150°C and 5 atm pressure. If using LiAlH₄, reaction occurs in dry ether followed by dilute acid workup.
6. The final product is pure primary propan-1-amine, with no secondary or tertiary amine impurities.

> **tip**
>
> CIE examiners require specific reagent and condition details, always state both, not just 'reduction'.

## Preparation of Aliphatic Amines: Ammonia Nucleophilic Substitution

Ammonia acts as a nucleophile to displace the halide leaving group from a halogenoalkane, forming an amine. This method produces a mixture of products, so it is less preferred than nitrile reduction for pure primary amines.

**Excess Ammonia** — A large molar excess of ammonia relative to the halogenoalkane, used to favour formation of primary amine over further substitution reactions

*Example:* A 10:1 NH₃:halogenoalkane ratio favours primary amine formation

**Worked example:** Explain why excess ammonia is required to favour ethylamine formation from bromoethane.

1. Step 1: Ammonia first attacks bromoethane to form ethylammonium bromide. A proton is then transferred to excess ammonia to form ethylamine:
2. $$CH_3CH_2Br + 2NH_3 \rightarrow CH_3CH_2NH_2 + NH_4Br$$
3. Step 2: Without excess ammonia, the product ethylamine is itself a nucleophile, and attacks another bromoethane molecule to form diethylamine.
4. Further substitution continues to form triethylamine and finally a quaternary ammonium salt, so excess NH₃ shifts equilibrium to favour the primary product.

> **warning**
>
> Even with excess ammonia, this reaction still produces a mixture of products, so it cannot give a 100% pure primary amine.

## Preparation of Aromatic Amines: Nitroarene Reduction

All primary aromatic amines are prepared by reducing a nitroarene starting material, which is obtained via nitration of the parent arene. The most common example is preparation of phenylamine from nitrobenzene.

**Worked example:** Write the preparation of phenylamine from nitrobenzene, including all reagents and conditions.

1. Step 1: Nitrobenzene is heated under reflux with tin (Sn) and concentrated hydrochloric acid:
2. $$C_6H_5NO_2 + 3Sn + 7HCl \rightarrow C_6H_5NH_3^+Cl^- + 3SnCl_2 + 2H_2O$$
3. Step 2: The intermediate phenylammonium salt is then deprotonated by adding sodium hydroxide solution to release free phenylamine:
4. $$C_6H_5NH_3^+Cl^- + NaOH \rightarrow C_6H_5NH_2 + NaCl + H_2O$$
5. CIE also accepts iron (Fe) instead of tin as the metal for this reaction.

> **exam_tip**
>
> Don't forget the NaOH workup step! Many candidates lose marks for only writing Sn/HCl and missing this final step.

## Common pitfalls

- **Wrong:** Calling NaOH the reducing agent for nitrobenzene
  - Why it fails: NaOH only deprotonates the intermediate salt, it does not act as a reducing agent
  - Correct: State Sn/Fe + concentrated HCl, heat under reflux, then add NaOH workup
- **Wrong:** Claiming ammonia substitution gives pure primary amine
  - Why it fails: Even with excess ammonia, further substitution produces a mixture of products
  - Correct: State nitrile reduction gives pure primary amine, which is why it is the preferred method
- **Wrong:** Using NaBH₄ to reduce nitriles or nitro groups
  - Why it fails: Sodium borohydride is not a strong enough reducing agent for these groups
  - Correct: Use LiAlH₄ or H₂/Ni for nitriles, Sn/HCl for nitroarenes
- **Wrong:** Using aqueous KCN for nitrile formation from halogenoalkanes
  - Why it fails: Aqueous KCN causes hydrolysis of the halogenoalkane to an alcohol, not substitution to nitrile
  - Correct: Use KCN dissolved in ethanol, heated under reflux to form the nitrile product

## Cheatsheet

| Amine Type | Method | Reagents & Conditions | Product Purity |
| --- | --- | --- | --- |
| Aliphatic Primary | Nitrile Reduction | H₂/Ni (heat/pressure) OR LiAlH₄/dry ether | Pure 1° amine |
| Aliphatic Primary | Halogenoalkane + NH₃ | Excess NH₃, ethanol, heat | Mixture (favours 1°) |
| Aromatic Primary | Nitroarene Reduction | Sn/Fe + conc HCl, reflux → NaOH workup | Pure 1° aromatic amine |

## What's next

Preparation of amines is a core topic for multi-step organic synthesis questions, which carry high marks in both Paper 2 and Paper 4 of CIE A-Level Chemistry. Mastery of these preparation routes is essential for planning synthetic pathways to target organic molecules, including dyes and pharmaceuticals. Next, you can build on this knowledge by exploring the properties and reactions of amines that are commonly tested in exams.

- [Properties and reactions of amines](https://www.owlsprep.com/study/cie-9701-u23-properties-and-reactions-of-amines/)
- [Polymers](https://www.owlsprep.com/study/cie-9701-u24-overview/)
- [Addition polymers](https://www.owlsprep.com/study/cie-9701-u24-addition-polymers/)

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