Key Difference – Esterification vs Transesterification
Esterification and transesterification are two important processes regarding esters. The key difference between esterification and transesterification is that an ester is formed from esterification whereas an ester is a reactant in transesterification.
An ester is an organic compound that is composed of C, H and O atoms. An ester is formed by replacing the –Oh group of a carboxylic acid with an alkoxy group. Esters are polar molecules. They are capable of forming hydrogen bonds. That is due to the presence of oxygen atoms. Esterification process produces esters whereas transesterification modifies esters.
CONTENTS
1. Overview and Key Difference
2. What is Esterification
3. What is Transesterification
4. Side by Side Comparison – Esterification vs Transesterification in Tabular Form
5. Summary
What is Esterification?
Esterification is the process of producing an ester from a carboxylic acid and an alcohol. An ester is formed when the –OH group of the carboxylic acid is replaced by the alkoxy group of the alcohol. The esterification process requires a catalyst for the progression. The catalyst is used to reduce the activation energy barrier of the esterification process. The catalyst is typically an acid. And also, heat should be provided as a source of energy. Otherwise, there will be no reaction taking place between carboxylic acid and the alcohol.
Water is produced as a byproduct during the esterification process. The –OH group removed from the carboxylic acid and the –H group removed from the alcohol, together forms a water molecule (H-OH). By changing the alcohol or the carboxylic acid, can obtain the esters with desired numbers of carbon atoms.
The esterification reaction is an equilibrium reaction between reactants and products. Therefore, the use of high amounts of reactants gives a high yield of ester along with water. dehydrating agents can be used to remove the water formed. And also, advanced methods such as distillation can also be used for the removal of water.
Figure 01: Ester Formation
Esterification Mechanism
In the esterification mechanism, first, the removal of –OH from carboxylic acid and removal of –H (proton) from alcohol occurs. This forms a carboxylic cation and an alcoholic nucleophile. These two components can react with each other forming the ester. The removed groups react with each other to form water.
What is Transesterification?
Transesterification is a process used to modify the structure of an ester. It includes an ester and alcohol as reactants. The transesterification occurs when the alkyl group of an ester is exchanged with the alkyl group of the alcohol. There, the alcohol acts as a nucleophile. The process requires a catalyst; either an acidic catalyst or a basic catalyst. The catalyst can reduce the activation energy barrier of the process.
Figure 02: Transesterification Process
Transesterification Mechanism
First, the alcohol is converted into a nucleophile by removing the terminal hydrogen atom as a proton. The transesterification initiates with the nucleophilic attack; alcohol attacks the carbon atom of the ester that is bonded to two oxygen atoms. That is because this carbon atom has a partial positive charge on it since the two oxygen atoms attract the bond electrons toward them (the oxygen atoms are more electronegative than carbon atoms).
The attack by alcoholic nucleophile results in the formation of an intermediate compound which has both the ester and the alcohol bonded with each other through the carbon atom attacked by the nucleophile. This intermediate compound is very unstable. There, a rearrangement occurs to obtain a stable form. This gives a new ester form. Transesterification gives the nucleophile as a byproduct.
What is the Difference Between Esterification and Transesterification?
Esterification vs Transesterification |
|
| Esterification is the process of producing an ester from a carboxylic acid and an alcohol. | Transesterification is a process used to modify the structure of an ester. |
| Use of Ester | |
| In esterification, the ester is the main product. | In transesterification, the ester is used as a reactant.. |
| Byproduct | |
| Esterification gives water as a byproduct. | Transesterification gives a nucleophile as a byproduct. |
| Catalyst | |
| Esterification requires an acidic catalyst. | Transesterification requires either an acidic or a basic catalyst. |
| Energy Source | |
| Esterification requires heat as the energy source. | Transesterification does not require energy. |
Summary – Esterification vs Transesterification
Esterification is the formation of an ester of carboxylic acids and alcohols. Transesterification is the process of modification of these produced esters. The difference between esterification and transesterification is that an ester is formed from esterification whereas an ester is a reactant in transesterification.
Reference:
1.“Conversion of Carboxylic Acids to Esters Using Acid and Alcohols (Fischer Esterification).” Master Organic Chemistry RSS. Available here
2.“Transesterification.” Wikipedia, Wikimedia Foundation, 16 Mar. 2018. Available here
Image Courtesy:
1.’Esters formation’By Laghi.l – Own work, (CC BY-SA 3.0) via Commons Wikimedia
2.’General transesterification mechanism’By Rifleman 82 – Own work, (Public Domain) via Commons Wikimedia