Preparation of an ester

Making an ester

Alcohols react with carboxylic acids to make esters.

The reaction is an equilibrium reaction.

Alcohol + carboxylic acid ester + water

The yield can be increased by removing water as it is formed. The reaction is catalysed by H+. A few drops of concentrated sulfuric acid will provide the H+ while also removing water.

A water bath will also speed up the reaction.

Take about 1–2 mL of ethanol in a test tube…

… and add 1 mL of pure ethanoic acid…

… followed by a few drops of concentrated sulfuric acid.

Warm in a water bath.

Take about 20 mL of sodium carbonate solution in a beaker and pour the contents of the test tube in, little at a time.

The sodium carbonate reacts with the unreacted acid, producing carbon dioxide gas.

Smell the beaker. The ester has quite a different odour from the parent acid and alcohol.

When the reaction has ceased, pour the contents of the beaker into a test tube.

Low mass alcohols and acids are miscible in water due to hydrogen bonding, but esters, which cannot hydrogen bond, are not miscible in water.

Esters also have low boiling points, so most of this ester has already boiled off.