Ester

Esterification

RCOOH + R'OH <=-----> RCOOR' + H2O

Physical Properties

- lower b.p. than alcohol because only dipolar forces and vdwf exist

- violatile esters: sweet and fruity smell

- not miscible with water but good solvents for many organic compound

Industrial Preparation

- Terylene: polyester; used to make wash-and-wear garments

Preparation of ethyl ethanoate

- Diagram showing the setup

- ester formation: Raise the temperature of oil bath to 140*C and maintain it. Allow the mixture in the funnel to drop into the flask at the same rate at which the distillate collects. Transfer the distillate to a separating funnel and shake with 30% solution of sodium carbonate. Invert the funnel and leaving the stop-tap open (to avoid high pressure of CO2). Test upper layer with blue litmus  paper to make sure all trace of acetic acid and sulphuric acid have been removed. Run off the lower layer and discard it.

- Distillation: Add solution of calcium chloride and shake well (to remove the alkanol remaining). Discard lower layer and  run the ester into a flask. Add enough anhydrous calcium chloride to cover the bottom of the flask, and leave it over night. Distill and collect the fraction between 74-79 *C.

- Concentrated sulphuric acid acts as catalyst and removes water formed (to shift equilibrium)

- Disadvantages: slow and reversible reaction; yield of ester not satisfactory

Industrial uses of ester

- as solvent  for thinner, paint, nail varnish removers

- as flavour enhancers in food processing industry because of its characteristic sweet and fruit smell

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