Organic Chemistry - Esters

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Unit 4: Organic Chemistry

Esters

R-COO-R'

PHYSICAL PROPERTIES

  • Mostly liquid at room temp.
  • Insoluble in water (despite their polarity) because they cant form H-bonds with H2O.

CHEMICAL STUFF

Preparation

  • Esters are prepared by warming an alcohol and a carboxylic acid under reflux with a few drops of conc. H2SO4 catalyst. This process is called esterification. IT IS A REVERSIBLE RXN.
    • C2H5OH + CH3COOH <-> CH3COOCH2CH3 + CH3CH2OH
  • Esters can also be obtained by reacting an alcohol with an acid chloride (a.k.a acyl chloride) at room temp. This way obtains a higher yield because the reaction is not reversible!
    • CH3CH2OH + CH3COCl -> CH3COOCH2CH3 + HCl

Hydrolysis

  • Esters are hydrolysed by heating under reflux with either an aqueous acid catalyst or an aqueous alkali catalyst.

Acid-catalysed hydrolysis:

  • CH3COOCH2CH3 + H2O <-> CH3COOH + CH3CH2OH
  • This is a reversible reaction!!!!

Base-catalysed hydrolysis:

  • CH3COOCH2CH3 + NaOH -> CH3COONa + CH3CH2OH
  • Here, the salt of the carboxylic acid is formed.
  • This reaction has a higher yield than the acid-catalysed reaction (it is not reversible).
  • If the carboxylic acid is required, the products are cooled and excess dilute strong acid (i.e. HCl or H2SO4) is added.
  • It is this reaction which produces soaps, a process known as saponification. A fat or oil (in other words, a natural ester) is heated with NaOH, to give a carboxylate salt and an alcohol!

Other reactions

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