Question

Why is esterification also called a dehydration reaction?

Answer 1

It is more commonly referred to as a `"condensation reaction..."`

Explanation:

And what is a `"condensation reaction?"` This is a chemical reaction when two molecules chemically combine to form a large molecule with the EXPULSION of a smaller molecule, such as water, or methanol, or hydrogen chloride...

The stability of the smaller molecule, i.e. water is an exceptionally stable molecule, thus provides a thermodynamic driving force to the condensation reaction....

Esterification of an alcohol, and a carboxylic acid is the classic example of a condensation reaction....

`ROH + HO(O=)CR' stackrel(Delta)rightleftharpoons RO(O=)CR' +H_2O`

..the water may be efficiently removed from the reaction mixture (by means of azeotropic distillation with benzene or toluene and collection in a trap), and the removal of water drives the equilibrium reaction to completion....

The male connector of the pictured Dean Stark trap is fitted to the reaction mixture in a condensation reaction. The female part of the trap is fitted to a reflux condenser. The water that results from the reaction between the alcohol and the carboxylic acid is distilled azeotropically with the benzene/toluene, and separates in the trap...often you can get an excellent idea of how complete the condensation reaction is by noting the volume of water collected in the trap...

With limited quantities of carboxylic acid....(i.e. something valuable) it may be preferable to make the acid halide as shown, and THEN react this with ONE equiv of alcohol in the presence of 1 equiv of a non-nucleophilic base..i.e.

`(i)` `RC(=O)OH + SOCl_2 rarr RC(=O)Cl + HCl+SO_2`

`(ii)` `RC(=O)Cl + HOR'stackrel(NR_3)rarrRC(=O)OR' + HCl*NR_3`