Properties of Amides

  • Amides are a class of organic compounds that contain a carbonyl group (C=O) directly linked to a nitrogen atom (N).
  • They have the general formula RCONR2, where R and R’ can be any alkyl or aryl group.
  • Amides can be primary, secondary or tertiary, depending on the number of carbon-containing groups attached to the nitrogen atom.
  • They have relatively high boiling points due to the presence of polar carbonyl and amide linkages, which allow for strong dipole-dipole and hydrogen bonding interactions.
  • Most amides are solids at room temperature, with the exception of formamide and acetamide which are liquids.

Preparation of Amides

  • Amides can be prepared by the reaction of amines with acyl chlorides or acid anhydrides in the presence of a base.
  • They can also be prepared by the ammonolysis of esters, where an ester reacts with ammonia to form an amide and an alcohol.
  • The third method involves the dehydration of ammonium carboxylates, where a carboxylic acid first reacts with ammonia to form an ammonium carboxylate, which is then dehydrated to yield an amide.

Reactions of Amides

  • Amides can be hydrolysed to form carboxylic acids and amines or ammonia.
  • This hydrolysis can occur under acidic or alkaline conditions, but the reaction is typically slow due to the resonance stabilization of the amide group.
  • Under strong acidic conditions, amides can undergo acid-catalysed hydrolysis, producing a carboxylic acid and an ammonium ion.
  • Conversely, under basic conditions, they undergo base-catalysed hydrolysis to produce a carboxylate ion and an amine.

Amides in Polymers and Biological Systems

  • Polyamides, such as nylon and kevlar, are important synthetic polymers that are made by the condensation polymerisation of diamines and dicarboxylic acids.
  • In proteins, peptide bonds are a type of amide bond formed between the carboxyl group of one amino acid and the amine group of another.
  • This peptide linkage allows for the formation of long, complex polypeptide chains, which are the building blocks of proteins.
  • Enzymes, which are bio-catalysts in biological reactions, also possess amide bonds in their structures. Their shape, and thus their function, often rely on the arrangement and properties of these bonds.