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5.5.4Unit 5. Transition Metals and Organic Nitrogen Chemistry

Amides — IAL Edexcel Linear (Chemistry) Revision Notes & Topical Questions

5 min read 6 parts Lesson 34 of 43 Unit quiz

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Part 1 of 6Structure and Properties

5.5.4 Amides
Functional group
  • An amide contains -CONH₂, or -CONHR and -CONR₂ when nitrogen carries other groups.
Naming
  • Ethanamide is CH₃CONH₂, and N-methylethanamide is CH₃CONHCH₃.
Not basic
  • The nitrogen lone pair is delocalised into the C=O group, so it is not available to accept a proton.
Hydrogen bonding
  • The N-H bonds allow hydrogen bonding, giving relatively high melting points.
Solubility
  • Small amides dissolve in water because their N-H and C=O groups form hydrogen bonds with water molecules.

Part 2 of 6Preparation

1
React an acyl chloride with concentrated ammonia: CH₃COCl + 2NH₃ → CH₃CONH₂ + NH₄Cl.
2
With a primary amine an N-substituted amide forms: CH₃COCl + 2CH₃NH₂ → CH₃CONHCH₃ + CH₃NH₃⁺Cl⁻.
3
Acid anhydrides give amides in a similar way but produce a carboxylic acid or carboxylate instead of HCl.
4
The reactions are vigorous at room temperature, and a white solid appears.

Part 3 of 6Reactions

Reactions
Acid hydrolysis
  • Heating with dilute HClCH₃CONH₂ + H₂O + HCl → CH₃COOH + NH₄Cl.
Alkaline hydrolysis
  • Heating with NaOHCH₃CONH₂ + NaOH → CH₃COONa + NH₃, ammonia turning red litmus blue.
Reduction
  • LiAlH₄ in dry ether reduces the amide to the amine: CH₃CONH₂ → CH₃CH₂NH₂.
Amine test
  • Warming with NaOH releases ammonia gas from a primary amide, a simple test confirming the -CONH₂ group.

Part 4 of 6Polyamides

Polyamides
Link
  • Nylon-6,6 contains the amide link -CONH- joining monomer units.
Monomers
  • Hexanedioyl dichloride and 1,6-diaminohexane react in condensation polymerisation, losing HCl.
Properties
  • Hydrogen bonds between chains make the polymer strong and give it a high melting point.
Naturally occurring
  • Proteins are also polyamides, built from amino acids joined by amide (peptide) links.
Hydrolysis
  • Boiling a polyamide with acid or alkali breaks the amide links and regenerates the monomers or their salts.

Part 5 of 6Worked Example

Question Write the equation for the alkaline hydrolysis of propanamide with sodium hydroxide.

  1. Propanamide is CH₃CH₂CONH₂.
  2. The amide is cleaved to give the sodium salt of the acid and ammonia.

Answer CH₃CH₂CONH₂ + NaOH → CH₃CH₂COONa + NH₃

Part 6 of 6Exam Checklist & Tips

5.5.4 – Key Points for the Exam

  • Amide A compound containing -CONH₂ or its N-substituted forms.
  • Acyl chloride A reactive compound RCOCl.
  • Hydrolysis Breaking a bond by reaction with water.
  • Polyamide A polymer with amide links.

Common Mistakes

  • Describing amides as bases like amines.
  • Forgetting that two moles of ammonia are needed.
  • Giving the products of alkaline hydrolysis as a carboxylic acid.
  • Reducing an amide with NaBH₄.

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