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Synthesis of Isopentyl Acetate (Banana Oil)
Esters are a class of compounds found widely in nature. Low molecular weight esters tend to have characteristic flavors and pleasant odors that are most often associated with essential oils, even though essential oils are a complex mixture. The purpose of this experiment is to synthesize isopentyl acetate (3-methylbutyl acetate) via an esterification reaction between acetic acid and isopentyl alcohol (3-methylbutanol), using concentrated sulfuric acid as a catalyst. The product will be washed, distilled, then characterized using NMR spectroscopy.
The ester functional group can be synthesized by many methods. The simplest approach is Fisher esterification. By this method, esters are produced by refluxing a carboxylic acid and an alcohol in the presence of a concentrated acid catalyst. To exploit Le Chatelier’s principle and shift the position of the equilibrium to the right we add an excessive of one of the reactants to the reaction mixture. Naturally, we choose the least expensive reactant, which, in this case, is the carboxylic acid. The reaction mechanism involves initial protonation of the carboxyl group, nucleophilic attack by the hydroxyl, proton transfer, and loss of water followed by loss of the catalyzing acid to produce the ester. The process is thermodynamically controlled yielding the most stable ester product. Typically, only primary and secondary alcohols are used in the Fisher method since tertiary alcohols are prone to elimination. In this lab, you will perform a Fisher esterification to synthesize isopentyl acetate from isopentyl alcohol and acetic acid.
About the author
Dean Antic, Ph.D., is a Senior NMR Applications Scientist, organic chemist and spectroscopist at Thermo Fisher Scientific, San Diego, CA. Formerly, Dean was an adjunct professor of chemistry at Northeastern Illinois University and a certified 9-12 chemistry instructor.