Fischer–Speier esterification

The esterification (also esterification or Fischer esterification called ) is a chemical reaction and was discovered by Emil Fischer.

Overview reaction

The reaction is an equilibrium reaction and condensation reaction in which an alcohol or a phenol with a carboxylic acid (more rarely, an inorganic acid ) reacts under acid catalysis to form an ester.

For acid catalysis of sulfuric acid, phosphoric acid or p-toluenesulfonic acid is often used.

Mechanism of acid-catalyzed esterification ( Fischer esterification)

Emil Fischer has recognized that even small amounts of acid increase the ester yield strong and not, as was customary, large amounts of acid are necessary. In fact, long before known that the addition of sulfuric acid favors the esterification. The first step of esterification is the protonation of the carboxylic acid to form a resonance stabilized cation.

The cation formed by protonation is attacked by a lone pair of the hydroxyl group of the alcohol nucleophile. The hydrogen atom of the original alkanol forms an intramolecular hydrogen bond to an oxygen atom of the carboxyl group and goes with this finally a bond.

Above in the last step, the resulting oxonium ion cleaves first water from a cation, which results in the ester after deprotonation.

Further esterification reactions

There are a number of other possibilities, alcohols and acids or acid derivatives convert to esters, such as the reaction between alcohol and acid chloride ( Schotten- Baumann method), alcohol and acid anhydride, the Steglich esterification or the Mitsunobu reaction. The transesterification allows the exchange of the alcohol or acid component of an existing ester.

Ester cleavage

The reverse reaction of esterification is the acid hydrolysis of esters (see hydrolysis). The basic or alkaline ester hydrolysis has a different reaction mechanism than the acidic and is therefore shown with hydrolysis explicitly.

Manufacturing process

Many chemical products are produced in a chemical reaction and then distilled. In the recovery of an ester of the two processes are linked. This method is called reactive distillation. During the reaction can be one or more products ( in the esterification: water) are removed by the evaporation. The chemical equilibrium is it always a new, and thereby a greater yield of the ester can be obtained. The process has the advantage that two steps can be combined. The apparatus required is low, and the process is inexpensive.