CI 13.5 - Esters

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  • CI 13.5 - Esters
    • Formation of Esters
      • Alcohol and carboxylic acid heated together under reflux in the presence of a few drops of concentrated sulphuric acid.
      • Water is formed as a by product, known as a condensation reaction.
        • Condensation reaction - two molecules reacting together to form a larger molecule with the elimination of a small molecule.
      • Ester link formed by the condensation reaction of hydroxyl group and the carboxyl group. known as esterification.
        • Esterification reaction is reversible, therefore controlled according to Le Chatelier's Principle.
          • Yield can be increased by: distilling off water as product or increasing concentration of cheap alcohol. Both move the position of equilibrium to the right.
          • Reversible reaction is ester hydrolysis.
    • Uses of Esters
      • Commonly used in food flavourings and perfumes
        • This is due to their strong sweet smells, often floral or fruity.
        • Ethyl butanoate - strawberry
        • 3-methylbutyl ethanoate - banana
        • 2-prop-1-enyl hexanoate - pineapple
    • Naming Esters
      • Named after alcohol and carboxylic acid from which they are derived.
        • Esters end in -oate
          • The first part comes from the alcohol. If it were ethanol, the preffix would be ethyl
          • The suffix is derived from the acid. If it were butanoic acid, the name would end in butanoate.
        • Group attached to C=O from the acid. Group attached to -O- from the alcohol.
    • Polyesters
      • Condensation polymers. Made by reacting a diol with a dicarboxylic acid.
        • Common polyester made from ethane-1,2-diol and benzene-1,4-dicarboxylic acid.
          • Also A-B polymerisation. Diol being A polymer and dicarboxylic acid being B.
    • Making Esters from Phenols
      • -OH group in phenol less reactive to esterification than -OH group of ethanol. Needs more vigorous reagent.
        • When ethanoic acid involved in esterification, process known as ethanoylation.
          • More vigorous ethanoylating agent is ethanoic anhydride. Made by eliminating molecule of water between two ethanoic acid molecules.
          • Ethanoic anhydride and ethanoyl chloride members of general group of reagents called acylating agents.
      • Phenol treated with acid anhydride under reflux.
        • Phenol reacts with acyl chloride under room temperature.
          • Both reactions must be carried out in absence of water
        • Both reactions must be carried out in absence of water


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