Explain Ester Synthesis | Esterification

What is ester?

Ester is an organic compound derived from an acid in which one hydroxyl group is replaced by an alkyl group. The hydroxyl group is replaced by a substitution reaction.  These esters on hydrolysis yield water and organic/inorganic acid. In this blog, we going to study ester synthesis.

General Structure of Ester:

Example:

Glycerides are esters that are produced as a result of the reaction between glycerol and fatty acid.

Some physical uses of ester:

• Easters give fruits aroma including apples, pears, and bananas.
• The sweet smell is used in essential oils.
• Low molecular weight ones are used in fragrance.
• Form high-grade solvents such as resin.
• Polyester is also made by esters which is a well-known polymer.

Process of Ester synthesis

Basically, esterification is a process that is used for esters synthesis. Esterification is a chemical process in which two reactants generally acids and alcohols react to form esters. There are different processes by which we can synthesis esters. These processes are discussed in detail below:

By esterification of carboxylic acids with alcohols:

It is a classic method of esterification in which carboxylic acid is heated in the presence of a suitable dehydrating agent with alcohol to produce esters.

RCO₂H + R′OH ⇌ RCO₂R′ + H₂O

This process is quite slow without a catalyst. Sulfuric acid is the usual catalyst used for this reaction.

By the esterification of a carboxylic acid with epoxides:

Carboxylic acids can also be esterified with epoxides which yield β-hydroxy ester.

RCO₂H + RCHCH₂O → RCO₂CH₂CH(OH)R

This reaction is used to produce vinyl ester resins.

Ester synthesis by Trans-esterification

Trans-esterification is a process that includes transferring one ester into another one. This method is broadly adept.

RCO₂R′ + CH₃OH → RCO₂CH₃ + R′OH

Trans-esterification uses acids and bases as a catalyst.

By the reaction of alcohol with acid anhydrides and acyl chlorides:

The reaction to form ester is the following:

RCOCl + R′OH → RCO₂R′ + HCl

(RCO)₂O + R′OH → RCO₂R′ + RCO₂H

Mostly this process is used for laboratory-scale procedures, as it is an expensive method.

Ester synthesis by Carbonylation:

Alkenes go through the process of hydro-esterification which use metal carbonyl as a catalyst. Propionic acid produced their esters commercially by this process:

C₂H₄ + ROH + CO → C₂H₅CO₂R

The process of preparation of methyl propionate is shown below:

C₂H₄+ CO + MeOH →MeO₂CCH₂CH₃