Chem 196
Fall 1998
Preparation of Banana Oil
Introduction
In this experiment, we prepare an ester, isopentyl acetate. This ester is often referred to as banana oil, since it has the smell of this fruit .
Isopentyl acetate is prepared by the direct esterification of acetic acid with isopentyl alcohol. An excess of acetic acid is used to shift the equilibrium to the right.
In the isolation procedure, much of the excess acetic acid and the remaining isopentyl alcohol are removed by extraction with water. Any remaining acid is removed by extraction with sodium bicarbonate. The ester is purified by distillation.
Procedure
Pour 3.0 mL (2.44 g, 0.0276 mole) of isopentyl alcohol and 4.0 mL (4.2 g, 0.070 mole) of glacial acetic acid into the given round-bottomed flask. Carefully add 1.0 mL of concentrated sulfuric acid to the contents of the flask, with swirling. Add several boiling stones to the mixture.
Assemble a reflux apparatus as demonstrated. Bring the mixture to a boil using a sand bath. Heat the mixture under reflux for 40 min. Remove the heating source and allow the mixture to cool to room temperature. Pour the cooled mixture in a test tube and carefully add 12 mL of cold water. Rinse the reaction flask with 2 mL of cold water and pour the rinsings in the test tube. Use a stirring rod to mix the contents somewhat. Let the two layers separate. Using a pasteur pipet take out the upper organic layer (density 0.87g/mL and discard the lower aqueous layer after making certain that the correct layer has been saved.
The crude ester in the organic layer has some acetic acid, which can be removed with extraction with 5% sodium bicarbonate solution. Carefully add 5 mL of the 5% base to the organic layer in the test tube and swirl the test tube until carbon dioxide gas is no longer evolved. Remove the lower layer and repeat the above extraction with 5% sodium bicarbonate solution until the aqueous layer is basic. Discard the basic washings and extract the organic layer with one 6 mL portion of water. Add 1 mL of saturated sodium chloride solution to aid in layer separation. Stir the mixture gently and carefully separate the lower aqueous layer and discard it. When the water has been removed, pour the organic layer in a flask and add 0.4 g sodium sulfate to dry the ester. Stopper the flask and swirl it gently. Allow the crude ester to stand until the liquid is still clear.
Assemble a distillation apparatus as demonstrated. Dry all glassware thoroughly before use. Carefully decant the ester into the distillation flask so that the drying agent is excluded. Add several boiling stones and distill the ester. The receiver must be cooled in an ice bath. Collect the fractions between 134 and 143 ° C in a dry flask
Weigh the product and calculate the percentage yield.
Obtain an infrared spectrum and include it with your report.