Acyl chlorides and acid anhydrides

Acyl chlorides

• Made by reacting a carboxylic acid with SOCl₂

  e.g.

  

• Very reactive

• Acyl chlorides have polar bonds

• They attract nucleophiles to the delta positive on the carbon of the C=O

  e.g. H₂O, NH₃, OH group on alcohols ^-CN

1. H₂O adds to the acyl chloride forming a dative covalent bond. The double bond breaks - addition stage

2. The double bond reforms and the chlorine leaves as Cl^- - elimination stage

3. A proton leaves

   Overall: nucleophilic addition-elimination

Acid anhydrides

• Made by dehydration of 2 carboxylic acid molecules

• Not as reactive as acyl chlorides

• Reaction with water: