How are most esters made?

1 Answer
Sep 21, 2016

#"Acid + alcohol "rarr" Ester + water"#

Explanation:

To repeat the given reaction with a carboxylic acid:

#RC(=O)OH + HOR' rightleftharpoons RC(=O)OR' + H_2O#

This means that to drive the reaction to completion, we need to remove 1 equiv of water. For many esters, simply heating the acid up in the alcohol will give the ester quantitatively (why? because the alcoholic solvent is in excess and drives the equilibrium to the right).

The acid halide may be simply prepared by heating the acid with thionyl chloride:

#RC(=O)OH + SOCl_2 rarr RC(=O)Cl + HCluarr + SO_2uarr#.

This is probably the best means of ester preparation. And of course it is useful if the acid or alcohol is something you have made on purpose and not a lab commodity. The acid halide may then be treated with a given alcohol in the presence of pyridine to sop up the liberated hydrogen halide:

#RC(=O)Cl + R'OH + C_5H_5N rarr RC(=O)OR' + C_5H_5N*HCl#