AQA, Chem4: Acylation

Revision notes on acylation from AQA Chem4

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  • Created by: anna
  • Created on: 04-06-13 15:09

Acylation

  • It is the introduction of an acyl group
  • The acyl group can come from either an acyl chloride or an acid anhydride
  • Both of which are derivatives of carboxylic acids with good leaving groups (Cl- and R-COO-)
  • Due to this the carbonyl group is open to nucleophilic attack

 

Reactions of acyl groups:

  • the mechanism for the reactions is nucleophilic addition-elimination
  • the nucleophile must have at least one replaceable H atom
  • examples of nucleophiles include water (HO-H), ethanol (C2H5O-H), ammonia (H2N-H) and amines (RHN-H or R2N-H)
  • the general equations are: R-COCl + Nuc-H --> R-CONuc + HCl (acyl chloride)
  • and RCOOCOR + Nuc-H --> R-CONuc + R-COOH
  • acyl chlorides always produce HCl and acid anhydrides always produce a carboxylic acid as a product
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More on acylation

Reacting an acyl group with...

  • water produces a carboxylic acid (R-COOH)
  • an alcohol produces an ester (R-COOR1)
  • ammonia produces an acid amide (R-CONH2)
  • a primary amine produces a substituted amide (R-CONHR)

Uses of acylation:

  • In drugs e.g. paracetamol and aspirin
  • acid anhydrides are preferred in these preparations as they are less corrosive, cheaper and less susceptible to hydrolysis
  • acyl chlorides however, react rapidly and violently producing fumes of HCl (it also needs anhydrous conditions)
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