MARS 6 Undergraduate Esterification Experiment

Introduction

Esters are organic compounds derived from carboxylic acids in which the acidic hydrogen has been replaced with an organic group. They are known for their pleasant odors and comprise the major flavor components of a number of fruits. In addition, they play a significant sole in primary metabolism and other biochemical processes.

Esters can be synthesized in a number of different ways. One common method is the acid catalyzed condensation of a carboxylic acid and an alcohol. The mechanism involves an initial protonation of the carboxylic acid to form a resonancestabilized cation. The addition of the alcohol to the cationic carbon and loss of one of the protons on the oxygen of the alcohol form a species called a geminal diol. Protonation of one of the hydroxyl groups in this diol, followed by loss of water, yields the ester product. To obtain significant yields of the product, the equilibrium must be shifted by either added excess of one of the starting materials or by removing water and/or the ester product.

In this experiment, 3-methyl-1-butanol is used in the esterification of ethanoic (acetic) acid to give a banana-smelling ester. Using conventional heating, the esterification reaction reaches equilibrium after a few hours of reflux. In this experiment, microwave heating in the CEM MARS 6^TM Synthesis microwave system is used to significantly accelerate the reaction. Both excess acetic acid and the removal of the water are utilized to drive the reaction to completion.