Esterification is a chemical reaction that combines an organic acid (RCOOH) with an alcohol (ROH) to form an ester (RCOOR) and water. The reaction is also known as the esterification reaction. The process of esterification involves five steps known as the esterification mechanism. The steps are as follows:

1. Formation of Cation: The organic acid takes a proton (a hydrogen ion) from the acid catalyst. This proton attaches to one of the single pairs on the oxygen which is double-bonded to the carbon.
2. Carbonation Delocalized: The oxygen atom that lost the proton forms a double bond with the carbon atom.
3. Formation of Tetrahedral Intermediate: The alcohol molecule donates a pair of electrons to the carbon atom, forming a tetrahedral intermediate.
4. Elimination of Water: The hydroxy group’s alcohol oxygen atom donates a pair of electrons to a carbon atom which makes a π bond by eliminating water.
5. Ester Formation: The final step is the formation of the ester.

Esterification can happen in three ways: from acid anhydride and alcohol, from acid chloride and alcohol, and from carboxylic acid and alcohol. The reaction requires an acid catalyst and heat to take place. Concentrated sulfuric acid is usually used as the catalyst, but dry hydrogen chloride gas is useful in some cases which incline towards aromatic sweet-smelling esters, the ones with the benzene ring.

An activity to show the formation of an ester is as follows:

1. Take 1 ml of ethanol (absolute alcohol) + 1 ml of glacial acetic acid in a boiling tube and mix the contents well.
2. Add a few drops of concentrated sulphuric acid to the mixture.
3. Heat the mixture gently for 2-3 minutes.
4. Cool the mixture and add 2 ml of water to it.
5. Smell the mixture. It will have a sweet smell of ethyl acetate.

Esters are sweet-smelling substances and are used in making perfumes, manufacturing of medicines, and manufacturing of paints and dyes.