26.4 - carboxylic acid derivatives

• What's a derivative or a carboxylic acid?


  A compound that can be hydrolysed to form the parent carboxylic acid.
• What do carboxylic derivatives have in common?


  They have a common sequence of atoms in their structure, known as an acyl group.
• Carboxylic acid derivatives


  Esters, acyl chlorides, acid anhydrides, and amides.
• How to name esters?


  Alkyl group of ester + name of parent acid with -oate suffix.

  
• Functional group of esters


  COO

  
• How are acyl chlorides named?


  Named after the parent carboxylic acid from which it is derived. Remove the -oic acid suffix and replace with -oyl chloride.

  
• How are acid anhydrides formed?


  Removal of one water molecule from two carboxylic acid molecules.

  
• Esterification


  The reaction of an alcohol with a carboxylic acid to form an ester.

  
• Reagents for esterification


  Alcohol and concentrated sulfuric acid catalyst.
• Conditions for esterification


  Solution is warmed.
• Smell of esters


  Sweet-smelling liquids
• Hydrolysis


  The chemical breakdown of a compound in the presence of water or in aqueous solution.
• What can esters by hydrolysed by?


  Aqueous acid or alkali.
• What is acid hydrolysis of esters the reverse of?


  Esterification
• What type of reaction is acid hydrolysis of esters?


  Reversible reaction.
• How to carry out acid hydrolysis of esters?


  1. The ester is heated under reflux with dilute aqueous acid.

  2. The ester is broken down by water, with the acid acting as a catalyst.
• Products of acid hydrolysis of esters


  A carboxylic acid and alcohol.
• What is alkaline hydrolysis also known as?


  Saponification.
• What type of reaction is alkaline hydrolysis?


  Irreversible reaction.
• How to carry out alkaline hydrolysis of esters?


  The ester is heated under reflux with aqueous hydroxide ions.
• Products of alkaline hydrolysis of esters


  Carboxylate ion (salt of ion and alkali) and alcohol.
• How can acyl chlorides be prepared?


  Directly from their parent carboxylic acid by reaction with thionyl chloride, SOCl₂.
• What are the other products of preparation of acyl chlorides?


  SO₂ and HCl as gases.
• Where should preparation of acyl chlorides be carried out?


  In a fume cupboard as the products are harmful.
• Reactions of acyl chlorides


  They are very reactive and can be easily converted into carboxylic derivatives, such as esters and amides, with good yields.

  
  

  They react with nucleophiles by losing the chloride ion whilst retaining the C=O double bond.
• Acyl chloride + alcohol =


  Ester + HCl
• Acyl chloride + phenols =


  Esters + HCl

  
• Why can't carboxylic acids form esters with phenols?


  They're not reactive enough.
• What are carboxylic acids less reactive than?


  Acyl chlorides and acid anhydrides.
• Acyl chloride + water =


  Carboxylic acid + HCl
• What observations are made when reacting acyl chlorides and water?


  A violent reaction with the evolution of dense steamy hydrogen fumes.
• Acyl chlorides + ammonia =


  Primary amide + NH₄Cl

  
• What do ammonia and amines act as when making amides from acyl chlorides?


  Nucleophiles by donating the lone pair of electrons on the nitrogen tom to an electron deficient species.
• Primary amide


  The nitrogen atom is attached to one carbon atom.
• Primary amide + acyl chloride =


  Secondary amide + CH₃NH₃⁺Cl⁻

  
• Secondary amide


  The nitrogen atom is attached to two carbon atoms.

  
• Reactions of acid anhydrides


  They react in a similar way to acyl chlorides with alcohols, phenols, water, ammonia, and amines.
• Are acid anhydrides or acyl chlorides more reactive?


  Acyl chlorides.
• Why might acid anhydrides be used instead of acyl chlorides?


  They are useful for some lab experiments where acyl chlorides may be too reactive.