Difference Between Esterification and Saponification

Main Difference – Esterification vs Saponification

Esters are organic compounds composed of C, H and O atoms. The presence of –COOR group indicates that a particular molecule is an ester. Esters are polar compounds due to the presence of oxygen atoms. They are also able to form hydrogen bonds with other compounds. An ester is formed from the reaction between a carboxylic acid and an alcohol in the presence of an acid catalyst. This synthesis process is called esterification. The opposite of the esterification is called saponification. The main difference between esterification and saponification is that esterification is the production of an ester from a carboxylic acid and an alcohol whereas saponification is the cleavage of an ester back into the carboxylic acid and alcohol.

Key Areas Covered

1. What is Esterification
      – Definition, Mechanism
2. What is Saponification
      – Definition, Mechanism
3. What is the Difference Between Esterification and Saponification
      – Comparison of Key Differences

Key Terms: Alcohol, Carboxylic Acid, Ester, Esterification, Saponification

What is Esterification

Esterification is the synthesis of an ester from a carboxylic acid and an alcohol. A catalyst should be used for the completion of this reaction in order to reduce the activation energy of the reaction. The catalyst should be an acid catalyst. Moreover, heat should be provided as a source of energy since energy is needed to cleave the C-OH bond of the carboxylic acid and remove the –OH group from it.

Esterification Mechanism

The reaction occurs through the removal of –OH group of the carboxylic acid and the proton of the –OH group of the alcohol. Then, the carboxylic cation and the alcoholic nucleophile react with each other, forming the ester.  Water molecules are a byproduct of this reaction. This is because the proton removed from the alcohol will react with the –OH group removed from the carboxylic acid, forming a water molecule. Pure ester can be obtained by adding a dehydrating agent.

Figure 01:  Esterification Process

The esterification reaction is an equilibrium. Therefore, in order to obtain a high yield of ester, we can add an excess of alcohol; if not, we can use a dehydrating agent that can remove the water produced in this reaction. Water can also be removed by some other method such as distillation.

What is Saponification

Saponification is the cleavage of an ester into carboxylic acid and alcohol. This is the backward reaction of esterification. This reaction needs the presence of a base and water. Due to the basic condition provided by the base, the carboxylate ion becomes more stable than the carboxylic acid form. Therefore, the carboxylate ion is separated from the ester molecule. This does not need heat energy. Water is needed to make the alcohol and the carboxylic acid by providing H⁺ and OH^–.

Saponification Mechanism

First, the OH- from the base attacks the carbon atom of –COO- bond in the ester. This is because the carbon atom is partially positively charged due to the presence of two oxygen atoms in its two sides. Therefore, it is an easy target for a nucleophile. Then the OH group make a bond with the carbon atom. Then a rearrangement takes place in order to become stable. Here, the –OR group from the alcohol is released, making carboxylic acid, which is the leaving group in this reaction. Since carboxylate ion is more stable in the basic medium, the resultant carboxylic acid is deprotonated. The removed proton is taken by the –OR group forming alcohol.

Figure 02: Saponification of a Fatty Acid

In the above example, triglyceride is an ester. It has 3 ester groups. In the presence of a base, it forms glycerol as the major product along with three carboxylate ions. Glycerol is an alcohol composed of three –OH groups.

Difference Between Esterification and Saponification

Definition

Esterification: Esterification is the synthesis of an ester from a carboxylic acid and an alcohol.

Saponification: Saponification is the cleavage of an ester into carboxylic acid and alcohol.

Reactants

Esterification: The reactants in esterification are carboxylic acid and an alcohol.

Saponification: The reactants of saponification are an ester, a base, and water.

Products

Esterification: The end products of esterification are ester and water.

Saponification: The end products of saponification are carboxylate ion and alcohol.

Catalyst

Esterification: The catalyst for esterification is an acid.

Saponification: The catalyst of saponification is a base.

Heat Requirement

Esterification: Esterification process requires heat energy.

Saponification: Saponification does not require heat energy.

Conclusion

Saponification is the opposite process of esterification. The main difference between esterification and saponification is that esterification is the production of an ester from a carboxylic acid and an alcohol whereas saponification is the cleavage of an ester back into the carboxylic acid and alcohol.

References:

1. “Saponification.” Chemistry LibreTexts. Libretexts, 21 July 2016. Web. Available here. 04 Aug. 2017. 
2.”Esterification -.” Chemoxy International. N.p., n.d. Web. Available here. 04 Aug. 2017

Image Courtesy:

1. “Saponification triglyceride-fr” By Pinpin – travail personnel from french wikipedia (CC BY-SA 3.0) via Commons Wikimedia