The key difference between esterification and saponification is that esterification forms an ester whereas saponification breaks down esters into its starting materials.
An ester is formed from a carboxylic acid and an alcohol. Therefore the esterification is the formation of an ester from a carboxylic acid and an alcohol. While, saponification forms the carboxylic acid and alcohol which are used to produce the ester.
CONTENTS
1. Overview and Key Difference
2. What is Esterification
3. What is Saponification
4. Side by Side Comparison – Esterification vs Saponification in Tabular Form
5. Summary
What is Esterification?
Esterification is the formation of an ester from the reaction between a carboxylic acid and an alcohol. This process requires a catalyst in order to reduce the activation energy barrier of the reaction. This catalyst is typically an acid catalyst. In addition, the reaction mixture should be heated because the esterification process requires energy (to cleave the C-OH bond of carboxylic acid to remove the –OH group).
Figure 1: Formation of an Ester via Esterification
Esterification process involves the removal of the hydroxyl group (-OH) of the carboxylic acid and the hydrogen atom of the hydroxyl group of the alcohol. During this process, when the –OH group is removed from the carboxylic acid, it acts as an electrophile. And when the proton of the alcohol is removed, it acts as a nucleophile. Therefore, this nucleophile attacks the electrophile formed from the carboxylic acid, and forms an ester. This gives a water molecule as a byproduct. Thus, the water molecule forms from the combination of –OH group from carboxylic acid and the proton from alcohol. Therefore, one can obtain pure ester using a dehydrating agent (in order to remove water from the reaction mixture).
What is Saponification?
Saponification is the breakdown of an ester into a carboxylic acid and an alcohol. It is the opposite of esterification. Saponification occurs in an aqueous medium in the presence of a base. The basic conditions of the medium make the carboxylate anion more stable than the carboxylic acid form. Therefore, the carboxylate ion separates from the ester. Saponification can occur in the absence of heat energy because it has no energy barrier. Here, the water molecules in the aqueous medium provide H+ ions, and the base provides OH– ions required for the formation of alcohol and carboxylic acid respectively.
Figure 2: General Process of saponification
Saponification reaction mechanism:
- Nucleophilic attack
- Rearrangement
- Removal of the leaving group
- Deprotonation
The hydroxyl ions (OH–) act as nucleophiles since they are rich with electrons. These ions can attack the ester bond (-C-O-O-) of the ester. They attack the carbon atom of this bond because the carbon atom has a partial positive charge due to the presence of oxygen atoms attached to the carbon atom. Then the OH ion forms a covalent bond with the carbon atom. But the carbon atom cannot have five covalent bonds since it is an unstable state of carbon. Therefore, a rearrangement step takes place after this bond formation. In the rearrangement step, the molecules become stable by the removal of –OR group (which came from the alcohol that was used to make the ester). It is the leaving group of the saponification reaction. A deprotonation of the carboxylic acid takes place because the carboxylate ion is the stable form in a basic medium.
What is the Difference Between Esterification and Saponification?
Esterification vs Saponification |
|
| Esterification is the formation of an ester from the reaction between a carboxylic acid and an alcohol. | Saponification is the breakdown of an ester into a carboxylic acid and an alcohol. |
| Requirement of Energy | |
| Esterification requires energy in the form of heat. | Saponification does not require external energy. |
| Reactants | |
| The reactants of esterification are alcohol and carboxylic acid. | The reactants of saponification are ester and base along with water. |
| Catalyst | |
| Esterification requires an acid catalyst. | Saponification requires a base catalyst. |
Summary – Esterification vs Saponification
Esterification and saponification are important chemical reactions in chemistry. Esterification is ester synthesis, and saponification is breakage of the ester bond. The key difference between esterification and saponification is that esterification process involves the formation of an ester whereas saponification process involves breaking down an ester into its starting materials.
Reference:
1. Helmenstine, Anne Marie, Ph.D. “Saponification Definition and Reaction.” ThoughtCo, Oct. 3, 2017, Available here.
2. “Saponification.” Wikipedia, Wikimedia Foundation, 3 Apr. 2018, Available here.
3. Esterification – Alcohols and Carboxylic Acids. Available here.
Image Courtesy:
1. “Esters formation” By Laghi.l – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “SaponificationGenera” By V8rik at English Wikipedia (CC BY-SA 3.0) via Commons Wikimedia