Fischer Esterification Experiment

Theoretical Background / Context

• All esters either naturally abundant or synthesized have a common chemical structure since they are derivatives of their corresponding carboxylic acids as shown below:

                   Figure 1. Common Chemical Structure of Esters

• Esters can be mainly prepared through esterification reaction; where carboxylic acids react with alcohols to form esters and water. 
• Esterification reactions are catalyzed by the presence of concentrated acids to force the reaction forward preventing it from going backward. 
• The general mechanism of the esterification reaction is displayed in the following scheme.

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                      Figure 2. Schematic Diagram for the Mechanism of Esterification Reaction

• The main role of acid in Fischer esterification reaction is acting as a catalyst since it is a dehydrating agent. It withdraws the water that is produced as a by-product of the reaction. 
• Consequently, this forces the reaction to go forwards and prevent it from going backward.
• Esters are characterized by possessing sweet odors.
• In addition, they are considered as the fundamental organic compounds that impart the sweet odour and taste of most fruits such as banana (isopentyl acetate), apple (methyl butyrate), cherry (benzyl butyrate), and ethyl propanoate which has a fruity aroma with distinctive ethyl propanoate structure.

Principle of Work

• An example Fischer esterification reaction is the methyl salicylate synthesis mechanism of methyl salicylate oil that possesses the odor of wintergreen oil. 
• The reaction and similar reactions proceeds between salicylic acid and methanol in presence of concentrated sulfuric acid as shown in the following scheme through the fischer esterification experiment:

    Figure 3. Schematic Diagram for Preparation of Methyl Salicylate from Salicylic Acid and  Methanol in Presence of Sulfuric Acid

• Finally, the formed wintergreen oil is extracted using diethyl ether with the aid of a separatory funnel.