Esterification reactions

The esterification reactions take place between a carboxylic acid and an alcohol, forming an ester and water.

Basically, esterification reactions are those in which a carboxylic acid reacts with an alcohol and produces ester and water.

When this reaction is carried out in a closed environment, it also tends to occur in reverse. This means that the water reacts with the ester and regenerates the carboxylic acid and alcohol, reaching chemical balance. This inverse reaction that occurs between the ester and the water is called hydrolysis.

Generically, we have:

Generic example of esterification reaction in equilibrium with hydrolysis

If hydrolysis occurs in an alkaline (basic) medium, we say that it is a basic hydrolysis, or saponification reactions , with the formation of an organic salt and an alcohol. Soap is an organic salt formed in this type of reaction.

If esterification occurs between a carboxylic acid and a primary alcohol, water as a product will be formed by the hydroxyl (OH) of the carboxylic acid and the hydrogen of the alcohol’s hydroxyl. How do we know that?

Well, a widely used way to determine the path or mechanism of the direct esterification reaction is through isotope 18 of oxygen in the hydroxyl of alcohol. This isotope of hydrogen is radioactive and is therefore a marked atom. That way, at the end of the reaction, it can be verified. In the diagram below, we can see better how it all happens. Note that oxygen-18 is in the hydroxyl of the alcohol and at the end of the reaction it remains in the ester molecule, thus showing that it was not used in the formation of water.

Esterification reaction with oxygen atom-18 to show the reaction path

But if the esterification reaction occurs with a secondary or tertiary alcohol or with an inorganic acid in place of the carboxylic acid, the opposite process will occur, that is, the water will be formed by the hydroxyl (OH) of the alcohol and the hydrogen will come from the hydroxyl of carboxylic acid.

Don’t stop now … There’s more after the publicity;)

The direct esterification reactions that occur between a carboxylic acid and an alcohol are widely used by the food industries because many esters formed are artificial flavorings , which are used in the production of candies, gum, ice cream, sweets etc.

Here are some examples:

Examples of esterification reactions with ester formation used as essences

However, these direct esterification reactions occur very slowly, which is why, in industrial terms, catalytic substances such as strong mineral acids (H 2 SO 4 or concentrated HCl) are often used. This type of reaction is called Fischer esterification because it was discovered in 1895 by Fischer and Speier.

There are esterification reactions that form triesters or triglycerides – molecules that have three functional groups of esters in their structure. To do this, simply react three fatty acid molecules (long-chain carboxylic acids with more than eleven carbon atoms) with glycerin (glycerol), which is a polyalcohol:

Formation of a triglyceride

Triglycerides are the main constituents of vegetable and animal oils and fats.

Larger molecule esters constitute oils and fats

But if the esterification reactions involve inorganic acids, inorganic esters will be formed. For example, when three molecules of nitric acid, which is an inorganic acid, react with glycerin, nitroglycerin (glycerin trinitrate) is formed, which is used as an explosive:

 

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