What are primary amines in the context of AS-Level Organic Chemistry?

Primary amines are organic compounds that contain a nitrogen atom bonded to one alkyl or aryl group and two hydrogen atoms. They are a key topic in the Cambridge International A Levels Chemistry syllabus under the study of nitrogen compounds. The general formula for primary amines is RNH2, where R represents an alkyl or aryl group.

How are primary amines named according to IUPAC nomenclature?

In IUPAC nomenclature, primary amines are named by identifying the alkyl group attached to the nitrogen atom and adding the suffix '-amine'. For example, CH3NH2 is called methylamine. If the amine group is part of a more complex molecule, it is named as an amino substituent, such as 2-aminoethanol.

What are the physical properties of primary amines?

Primary amines generally have higher boiling points than hydrocarbons of similar molecular weight due to hydrogen bonding between the amine molecules. They are typically soluble in water, especially those with shorter carbon chains, because they can form hydrogen bonds with water molecules. This solubility decreases as the length of the carbon chain increases.

How are primary amines synthesized in the laboratory?

Primary amines can be synthesized through several methods, including the reduction of nitriles, amides, or nitro compounds. One common method is the Gabriel synthesis, which involves the alkylation of phthalimide followed by hydrolysis to yield the primary amine. Another method is the reduction of nitriles using hydrogen gas and a catalyst or using lithium aluminum hydride.

What are some common reactions involving primary amines?

Primary amines participate in various chemical reactions, such as acylation, where they react with acyl chlorides to form amides. They can also undergo alkylation to form secondary and tertiary amines. Additionally, primary amines can react with nitrous acid to form diazonium salts, which are important intermediates in the synthesis of azo dyes and other aromatic compounds.

Why is "Omitting 'ethanol', 'pressure' or 'excess ammonia'." a common mistake in Primary amines?

Why it happens: Giving incomplete conditions. How to avoid it: All three: NH₃ in ethanol, heated under pressure, excess. Source: 9701 Examiner Reports 2022-2024

Why is "Confusing the NH₃ reaction with the KCN (nitrile) reaction." a common mistake in Primary amines?

Why it happens: Both are nucleophilic substitutions of halogenoalkanes. How to avoid it: NH₃ → amine; KCN → nitrile.

Why is "Treating amines as acidic." a common mistake in Primary amines?

Why it happens: Forgetting the N lone pair. How to avoid it: Amines are BASES — they accept H⁺ onto the nitrogen lone pair.

Why is "Assuming the NH₃ route gives a pure primary amine." a common mistake in Primary amines?

Why it happens: Ignoring further substitution. How to avoid it: The amine is also a nucleophile → a mixture of 1°/2°/3° amines forms (use excess NH₃ to limit it).

Nitrogen compounds(AS-Level Organic Chemistry)Cambridge International A Level Chemistry 9701

Primary amines

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Primary Amines — Cambridge International AS & A Level Chemistry 9701 (2025-2027 syllabus)

How primary amines are made at AS Level: the nucleophilic substitution of a halogenoalkane by excess ammonia in ethanol, heated under pressure.

What you’ll learn

Mapped to the Cambridge International A Level 9701 syllabus (2025-2027).

19.1.1 — Recall how amines can be produced: the reaction of a halogenoalkane with NH₃ in ethanol heated under pressure. (Classification of amines is not tested at AS Level.)

Making a primary amine from a halogenoalkane

Ammonia acts as a nucleophile and substitutes the halogen, giving an amine.

A primary amine has the –NH₂ group attached to one carbon (R–NH₂).

Preparation: heat a halogenoalkane with ammonia (NH₃) dissolved in ethanol, under pressure (a sealed tube). Ammonia acts as a nucleophile and replaces the halogen by nucleophilic substitution: $\text{CH}_3\text{CH}_2\text{Br} + \text{NH}_3 \rightarrow \text{CH}_3\text{CH}_2\text{NH}_2 + \text{HBr}$ (In practice, with NH₃ in excess: $\text{CH}_3\text{CH}_2\text{Br} + 2\text{NH}_3 \rightarrow \text{CH}_3\text{CH}_2\text{NH}_2 + \text{NH}_4\text{Br}$ , the second NH₃ mopping up the HBr.)

Why ethanol and pressure?

Ethanol as solvent prevents the competing reaction with water (which would give an alcohol).
Heating under pressure keeps the volatile ammonia in the reaction mixture.

Why use excess ammonia? The amine product is itself a nucleophile and can react further to give secondary and tertiary amines (and quaternary salts). Excess NH₃ maximises the yield of the primary amine.

Halogenoalkane + NH₃ in ethanol, heated under pressure.
Mechanism: nucleophilic substitution (NH₃ is the nucleophile).
Use excess NH₃ to favour the primary amine.

How it’s examined

At AS this is a short recall question — the reagents and conditions for making an amine, often within a synthesis route. Examiner reports flag omitting 'in ethanol' / 'excess ammonia' and confusing this with the KCN (nitrile) reaction.

Sources: Cambridge International AS & A Level Chemistry 9701 syllabus (2025-2027), section 19.1; 9701 Examiner Reports 2022-2024; 9701/22 May/Jun 2024 question paper and mark scheme. Last reviewed 2026-05-20.

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Step-by-step worked examples — Primary amines

Step-by-step solutions to past-paper-style questions on primary amines, written exactly the way a tutor would explain them at the board.

1Preparing a primary amine (3 marks)
Getting started• preparation
Question
State the reagents and conditions to convert bromoethane into ethylamine, and write the equation.
Step-by-step solution
1. Step 1
  Reagents/conditions: excess NH₃ in ethanol, heated under pressure.
2. Step 2
  Equation:
  $\text{CH}_3\text{CH}_2\text{Br} + 2\text{NH}_3 \rightarrow \text{CH}_3\text{CH}_2\text{NH}_2 + \text{NH}_4\text{Br}$
Answer
Excess NH₃ in ethanol, heat under pressure; CH₃CH₂Br + 2NH₃ → CH₃CH₂NH₂ + NH₄Br.
Examiner tip
Include 'in ethanol', 'under pressure' and 'excess ammonia'.
2Amine as a base (2 marks)
Getting started• basicity
Question
Write the equation for ethylamine reacting with hydrochloric acid and name the salt.
Step-by-step solution
1. Step 1
  The N lone pair accepts H⁺ → an ammonium-type salt.
  $\text{CH}_3\text{CH}_2\text{NH}_2 + \text{HCl} \rightarrow \text{CH}_3\text{CH}_2\text{NH}_3^+\text{Cl}^-$
Answer
CH₃CH₂NH₂ + HCl → CH₃CH₂NH₃⁺Cl⁻ (ethylammonium chloride).
Examiner tip
Amines are bases — they accept a proton onto the N lone pair.
3Why excess ammonia? (2 marks)
Building confidence• conditions
Question
Explain why excess ammonia is used when making a primary amine.
Step-by-step solution
1. Step 1
  The amine product is also a nucleophile and can react further with the halogenoalkane.
2. Step 2
  Excess NH₃ reduces this further substitution, maximising the primary amine yield.
Answer
Excess NH₃ limits further substitution (to 2°/3° amines), maximising the primary amine.
4Basicity of amines (3 marks)
Building confidence• basicity
Question
Explain why ethylamine acts as a base and why it is a stronger base than ammonia. (3)
Step-by-step solution
1. Step 1
  The N lone pair accepts a proton (H⁺) → it is a Brønsted–Lowry base.
2. Step 2
  The ethyl group is electron-donating (+I effect), pushing electron density onto N.
3. Step 3
  This makes the lone pair more available to accept H⁺ → stronger base than ammonia.
Answer
Lone pair accepts H⁺ (base); the alkyl +I effect makes that lone pair more available → stronger base than NH₃.
Examiner tip
Link basicity to the AVAILABILITY of the N lone pair, increased by electron-donating alkyl groups.
5Amine from a nitrile (3 marks)
Stretch• preparation
Question
Give the reagents and product when propanenitrile is reduced, and write the equation.
Step-by-step solution
1. Step 1
  Reduce with LiAlH₄ (or H₂ with a Ni catalyst).
2. Step 2
  The –CN becomes –CH₂NH₂ → propylamine.
  $\text{CH}_3\text{CH}_2\text{CN} + 4[\text{H}] \rightarrow \text{CH}_3\text{CH}_2\text{CH}_2\text{NH}_2$
Answer
LiAlH₄ (or H₂/Ni); CH₃CH₂CN → CH₃CH₂CH₂NH₂ (propylamine).
Examiner tip
Reducing a nitrile gives a primary amine with the SAME number of carbons as the nitrile.
6Comparing the two amine routes (4 marks)
Stretch• preparation, comparison
Question
Compare making a primary amine by (a) reacting a halogenoalkane with excess NH₃ and (b) reducing a nitrile. (4)
Step-by-step solution
1. Step 1
  (a) NH₃ route: simple, but the amine is a nucleophile too → a mixture of 1°/2°/3° amines (lower purity).
2. Step 2
  Excess NH₃ helps but does not give a single clean product.
3. Step 3
  (b) Nitrile reduction: gives a clean primary amine (no over-substitution).
4. Step 4
  But the nitrile route adds a carbon (via KCN first), so it changes the chain length.
Answer
NH₃ route: simple but gives a mixture; nitrile reduction: clean 1° amine but extends the chain by one C.
Examiner tip
Choose the route by what matters: purity (nitrile reduction) vs keeping the carbon count (NH₃).

Key Formulae — Primary amines

The formulae you need to memorise for primary amines on the Cambridge International A Level 9701 paper, with every variable defined in plain English and a note on when to use it.

General formula of primary amines
$C_nH_{2n+1}NH_2$
$n$
number of carbon atoms
When to use
Deducing a primary amine's formula (also written CₙH₂ₙ₊₃N).

Key Definitions and Keywords — Primary amines

Definitions to memorise and the exact keywords mark schemes credit for primary amines answers — sharpened from recent examiner reports for the 2026 Cambridge International A Level 9701 sitting.

Primary amine
Examiner keyword
A compound with an –NH₂ group attached to one carbon (R–NH₂).
Basicity of amines
Examiner keyword
Amines are bases because the N lone pair accepts a proton; alkyl groups (+I) increase the lone pair's availability → stronger base than NH₃.
Amine preparation
Examiner keyword
From a halogenoalkane + excess NH₃ in ethanol (heat, pressure), or by reducing a nitrile with LiAlH₄ / H₂ + Ni.
Amine salt
Examiner keyword
Formed when an amine reacts with an acid (e.g. ethylammonium chloride from ethylamine + HCl).

Common Mistakes and Misconceptions — Primary amines

The traps other students keep falling into on primary amines questions — taken from recent Cambridge International A Level 9701 examiner reports and mark schemes — and how to avoid them.

✕Omitting 'ethanol', 'pressure' or 'excess ammonia'.
9701 Examiner Reports 2022-2024
Why it happens
Giving incomplete conditions.
How to avoid it
All three: NH₃ in ethanol, heated under pressure, excess.
✕Confusing the NH₃ reaction with the KCN (nitrile) reaction.
Why it happens
Both are nucleophilic substitutions of halogenoalkanes.
How to avoid it
NH₃ → amine; KCN → nitrile.
✕Treating amines as acidic.
Why it happens
Forgetting the N lone pair.
How to avoid it
Amines are BASES — they accept H⁺ onto the nitrogen lone pair.
✕Assuming the NH₃ route gives a pure primary amine.
Why it happens
Ignoring further substitution.
How to avoid it
The amine is also a nucleophile → a mixture of 1°/2°/3° amines forms (use excess NH₃ to limit it).

Practice questions

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Primary amines — frequently asked questions

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Primary amines

Short Study Notes in the form of Slides

Short Study Notes — Primary amines

Detailed Notes

What you’ll learn

How it’s examined

1Preparing a primary amine (3 marks)

2Amine as a base (2 marks)

3Why excess ammonia? (2 marks)

4Basicity of amines (3 marks)

5Amine from a nitrile (3 marks)

6Comparing the two amine routes (4 marks)

General formula of primary amines

Primary amine

Basicity of amines

Amine preparation

Amine salt

✕Omitting 'ethanol', 'pressure' or 'excess ammonia'.

✕Confusing the NH₃ reaction with the KCN (nitrile) reaction.

✕Treating amines as acidic.

✕Assuming the NH₃ route gives a pure primary amine.

Practice questions

Past paper style quiz

Assess your understanding

Video lesson

Primary amines — frequently asked questions