Amides (Edexcel International A Level Chemistry)

• Amides are organic compounds with an -CONR₂ functional group
• They can be prepared from the condensation reaction between an acyl chloride and ammonia or amine
• In a condensation reaction, two organic molecules join together and in the process eliminate a small molecule
• In this case, the acyl chlorides and ammonia or amine join together to form an amide and eliminate an HCl molecule

Condensation reaction

• The chlorine atom in acyl chlorides is electronegative and draws electron density from the carbonyl carbon
• The carbonyl carbon is therefore electron-deficient and can be attacked by nucleophiles
• The nitrogen atom in ammonia and amines has a lone pair of electrons which can act as a nucleophile and attack the carbonyl carbon
• As a result, the C-Cl bond is broken and an amide is formed
• Whether the product is a substituted amide or not, depends on the nature of the nucleophile
  • Primary and secondary amines will give a substituted amide
  • The reaction of acyl chlorides with ammonia will produce a non-substituted amide

Acyl chlorides undergo condensation reactions with ammonia and amines to form amides

• Note that ammonia is basic and the inorganic product is acidic, so there will be a reaction between the two molecules

NH₃ + HCl → NH₄Cl

• We can therefore write the overall equation for the reaction of propanoyl chloride and ammonia as

CH₃CH₂COCl + 2NH₃ → CH₃CH₂CONH₂ + NH₄Cl