Edexcel A Level Chemistry:复习笔记7.5.5 Amide Chemistry

Amide Formation

 

  • 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

     

7.5-Carboxylic-Acids-Derivatives-Condensation-of-Acyl-Chlorides_1

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

Polyamide Formation

Amide link

  • Polyamides are also formed using condensation polymerisation

7.7-Polymerisation-Amide-Link

An amide link - also known as a peptide link - is the key functional group in a polyamide

Monomers

  • A diamine and a dicarboxylic acid are required to form a polyamide
    • A diamine contains 2 -NH2 groups
    • A dicarboxylic acid contains 2 -COOH groupspolyamide

The monomers for making polyamides

Formation of polyamides

7.7-Polymerisation-Making-an-Amide-Link

This shows the expulsion of a small molecule as the amide link forms

  • Nylon 6,6 is a synthetic polyamide
  • Its monomers are 1,6-diaminohexane and hexane-1,6-dioic acid
    • The ‘6,6’ part of its name arises from the 6 carbon atoms in each of Nylon 6,6 monomers

7.7-Polymerisation-Making-Nylon-66

Nylon 6,6 is a synthetic polyamide made using diamine and dicarboxylic acid monomers

Kevlar

  • Kevlar is another example of a polymer formed through condensation polymerisation
  • The polymer chains are neatly arranged with many hydrogen bonds between them
  • This results in a strong and flexible polymer material with fire resistance properties
  • These properties also lend Kevlar to a vital application in bullet-proof vests
  • The monomers used to make Kevlar
    • 1,4-diaminobenzene
    • Benzene-1,4-dicarboxylic acid

7.7-Polymerisation-Making-Kevlar

Kevlar is made using a diamine and dicarboxylic acid monomers

 

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