Experiment 1: Synthesis of the Fragrance of Banana
Esters are extremely common compounds; we consume and use them every day.
To synthesize ester, one of the simplest and oldest known organic reactions is the
dehydration of a carboxylic acid and an alcohol to form an ester. This reaction is
called the Fischer esterification in the honor of Emil Fischer, a German chemist.
Isoamyl acetate (or isopentyl acetate and is also known as banana oil) is a
naturally occurring compound that possesses a distinctive pleasant odor of banana,
and has low toxicity. It is found in bananas as well as many other organisms.
Coincidentally, this oil is also the alarm pheromone of the honeybee.
O
OH
H+
O
+
+
OH
Isoamyl
Alcohol
O
H
H
O
Glacial Acetic
Acid
Isoamyl Acetate
Experimental Procedure
1. Transfer isoamyl alcohol (1.0 mL) and glacial acetic acid (2.0 mL) into a 5-mL
round-bottomed flask. Carefully add 3 drops of concentrated sulphuric acid to
the contents of the flask. Put a few anti-bumping granules into the mixture.
[CAUTION: Extreme care must be exercised to avoid contact with concentrated
sulphuric acid. It will cause serious burns if it is spilled on the skin. If it
comes in contact with the skin or clothes, it must be washed off immediately with
excess water. Clean up all spills immediately.]
2.
Assemble a reflux apparatus and boil the
mixture with a sand bath on a hotplate. Boil
the mixture under reflux for at least 30
minutes. Remove the heating source and
allow the mixture to cool to room temperature.
3.
Pour the mixture into a 25 mL-beaker and mix
with 8 mL 10% NaHCO3(aq) slowly, stir well.
Transfer the cooled mixture into a screw-cap
test tube and carefully discard the aqueous
layer with a dropper.
4.
Repeat the washing process in step 3 with
another 8 mL of NaHCO3(aq).
1 of 2
5.
6.
Collect the organic layer and rinse it with brine (1.0 mL).
Collect the organic layer into a screw-cap test tube. Add enough amount of
anhydrous sodium sulphate for dehydration. Decant the supernatant into a
5-mL round-bottom flask. Immediately cap the test tube.
7.
Assemble a simple distillation apparatus. Purify the isoamyl acetate by simple
distillation and report the boiling point in 3 significant figures.
(Boiling point of isoamyl acetate = _______ oC)
8.
Seek help with a technician to get an IR spectrum of the distilled product.
Check your spectrum against a standard one.
2 of 2