Amines and amides
Key idea: Amines accept protons using nitrogen's lone pair. Amides contain nitrogen bonded to a carbonyl group; hydrolysis splits their C–N bond, with the products' charges set by acid or alkali.
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Guided lessons · coming soon
Guided lesson
Guided steps
- Classify each compound by the bonds next to nitrogen.
- Compare amine nitrogen with nitrogen beside a carbonyl group.
- Follow proton acceptance and amine salt formation.
- Choose the ion and count amines per acid molecule.
- Explain basicity and write the sulfate-salt equation.
- Follow DCC coupling of an acid and an amine.
- Keep the nitrogen side group when the amide link breaks.
- Choose both acid-hydrolysis products.
- Draw amide formation and write balanced alkaline hydrolysis.
- Name acid-hydrolysis products and write the balanced equation.
- Recall reagents before reading the reaction map.
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ContinueThe fishy smell of rotting fish comes from amines, and both nylon and proteins contain amide links. This lesson covers how amines act as bases, how an amine and a carboxylic acid are joined to make an amide, and how amides are hydrolysed.
Check your understanding 1 Look next to nitrogen
Classify CH₃CH₂NH₂ and CH₃CONH₂. Is a carbonyl carbon joined directly to the nitrogen?
Show answer
CH₃CH₂NH₂ is an amine. CH₃CONH₂ is an amide: its nitrogen is joined directly to C=O.
Amines and amides
An amine is like ammonia with one or more hydrogen atoms replaced by carbon groups. Ethylamine is CH₃CH₂NH₂.
An amide has a nitrogen atom bonded directly to a C=O group. Ethanamide is CH₃CONH₂. In N-ethylethanamide, CH₃CONHCH₂CH₃, the “N-” shows that the ethyl group is attached to the nitrogen.
In an amide, the nitrogen lone pair is spread into the carbonyl group, so it is less available to accept a proton than the lone pair in an amine. The position of C=O changes more than the compound’s name.
Amines as bases
Like ammonia, an amine has a lone pair of electrons on its nitrogen atom, which can accept a proton. So amines are bases, and react with acids to form salts:
Check your understanding 2 Follow the proton
Ethylamine neutralises both acidic protons of sulfuric acid. Choose ethylamine’s role and the ion formed, then find how many amine molecules react per H₂SO₄ molecule.
Show answer
The amine acts as a base and forms CH₃CH₂NH₃⁺. Two amine molecules accept the two protons of one sulfuric acid molecule; their two positive charges balance SO₄²⁻.
Guided practice 1
Ethylamine and sulfuric acid
Problem
Try this before viewing the solution
Hints
Hint 1
the base
What on the nitrogen can accept a proton?Hint 2
the salt
Sulfuric acid can give two protons, so two amine molecules react with one H₂SO₄.Show solution step by step
Why it is a base
Method
Look at the nitrogen atom.Reason
A base accepts protons.Working
Answer
The lone pair on nitrogen accepts a proton: CH₃CH₂NH₂ + H⁺ → CH₃CH₂NH₃⁺.The salt
Working
Answer
2CH₃CH₂NH₂ + H₂SO₄ → (CH₃CH₂NH₃)₂SO₄, ethylammonium sulfate, which contains CH₃CH₂NH₃⁺ and SO₄²⁻ ions.
Quick check
Making amides
A carboxylic acid and an amine join to form an amide in the presence of a coupling reagent, DCC (dicyclohexylcarbodiimide). This is a condensation reaction: the elements of water are removed. The scheme below shows the organic conversion. DCC takes up the elements of water and forms a urea by-product. You do not need to draw DCC or that by-product.
Hydrolysis of amides
Like esters, amides are hydrolysed by heating with aqueous acid or aqueous alkali. The C–N bond breaks, giving a carboxylic acid part and an amine (or ammonia) part. As with esters, the conditions decide which form each part is in:
| Amide | Heated with aqueous acid | Heated with aqueous NaOH |
|---|---|---|
| ethanamide | ethanoic acid + ammonium salt | sodium ethanoate + ammonia |
| N-ethylethanamide | ethanoic acid + ethylammonium salt | sodium ethanoate + ethylamine |
In acid, the ammonia or amine is protonated; in alkali, the carboxylic acid is turned into its salt.
Check your understanding 3 The nitrogen part in acid
N-Ethylethanamide is heated with excess dilute hydrochloric acid. Choose the forms of the nitrogen-containing product and the acid-derived product.
Show answer
The products are ethanoic acid and ethylammonium chloride. The ethyl group stays on nitrogen when the C–N bond of the amide link breaks; the amine then accepts a proton.
Exam-style question 1
Making and hydrolysing amides
Examination question
Try this before viewing the solution
Show solution step by step
Making the amide
2 marksMethod
Give the coupling reagent and show the organic conversion.Reason
DCC joins a carboxylic acid and an amine.Working
Answer
DCC: CH₃CH₂COOH + CH₃NH₂ → (DCC) CH₃CH₂CONHCH₃Hydrolysis
2 marksWorking
Answer
CH₃CH₂CONH₂ + NaOH → (heat) CH₃CH₂COONa + NH₃: sodium propanoate and ammonia.
Self-mark with the mark scheme
Tick each mark point that your answer includes.
Credit the reagent, the amide, and each product of the alkaline hydrolysis.
Check your understanding 4 Hydrolysis in acid
Propanamide, CH₃CH₂CONH₂, is heated with excess dilute hydrochloric acid. Name the products and write the equation.
Show hint
In acid, the carboxylic acid stays as the acid, but the ammonia is protonated.
Show answer
Propanoic acid and ammonium chloride: CH₃CH₂CONH₂ + H₂O + HCl → (heat) CH₃CH₂COOH + NH₄Cl
Connect the derivative reactions
The map brings together the reactions of carbonyl compounds, carboxylic acids, esters, amines and amides. Cover the reagents and try to recall each one from the starting compound and the product.
Swipe or scroll sideways to inspect the complete overview.
Read the reaction routes
| Starting compound(s) | Reagents and conditions | Product(s) |
|---|---|---|
| Propanal | LiAlH₄, or H₂ with Ni catalyst | Propan-1-ol |
| Propanal | Acidified K₂Cr₂O₇ or KMnO₄, heat | Propanoic acid |
| Propanone | LiAlH₄, or H₂ with Ni catalyst | Propan-2-ol |
| Ethanoic acid + ethanol | Concentrated H₂SO₄ catalyst, heat; reversible | Ethyl ethanoate + water |
| Ethanoic acid + ethylamine | DCC; organic transformation shown | N-ethylethanamide (DCC-derived by-product omitted) |
Common mistakes
- Saying that an amine forms an amide when it reacts with an acid such as HCl. It forms a salt.
- Using concentrated sulfuric acid, instead of DCC, to make an amide.
- Giving ammonia, rather than an ammonium salt, as a product of hydrolysis in acid.
- Giving the carboxylic acid, rather than its salt, as a product of hydrolysis in alkali.
- Losing the ethyl group when hydrolysing N-ethylethanamide: it becomes ethylamine.
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Syllabus and review details
- GCE A-Level H1 Chemistry 2027 · 8873-2027
8873 (2027), complete syllabus
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