CHEM& 131
Banana Oil Lab
1
Preparation of Banana Oil
Introduction
Many of the simple esters have pleasant fragrances which we find similar to that of fruits and flowers. These
esters have been synthesized in laboratories and are sometimes used to duplicate natural fragrances and flavors
in commercially prepared desserts and beverages. Interestingly, they are not used in expensive perfumes
because the ester group is not stable to perspiration. It can decompose to produce acids which often have
unpleasant odors.
The ester prepared in this experiment has the fragrance of bananas. It has another interesting characteristic. It is
identical to the pheromone of the honeybee. A pheromone is a chemical secreted by an organism that results in a
specific response from other members of the same species. When a worker bee stings its victim, this pheromone
is secreted along with the venom. The pheromone alerts other bees to join in the attack on the intruder.
In this experiment isopentyl acetate will be prepared from the reaction of acetic acid and isopentyl alcohol. The
reaction does not yield significant amounts of the ester unless the reaction is forced toward the production of the
ester. It can be forced by using an excessive amount of one of the starting materials. We will use an excess of
acetic acid as it is less expensive than isopentyl alcohol. A small amount of sulfuric acid will be used as a catalyst.
After the reaction is complete, the excess acetic acid and the sulfuric acid can be neutralized with sodium
bicarbonate and subsequently separated from the water-insoluble ester.
Procedure
1. Using a graduated pipet, place approximately 0.7 mL of isopentyl alcohol (also called isoamyl alcohol) in a
5-mL conical vial.
2. Add approximately 1.4 mL of glacial acetic acid using a graduated pipet.
3. Using a disposable glass Pasteur pipet, add two or three drops of concentrated sulfuric acid.
4. Add a magnetic spin vane (magnetic stir bar).
5. Assemble a reflux apparatus using a water-cooled condenser. (Refer to figure.) Top the apparatus with a
drying tube packed with calcium chloride held in place with a small amount of cotton.
6. Using a hot plate equipped with an aluminum block, bring the mixture to a boil. If desired, an aluminum
collar can be wrapped around the vial to better control the temperature. Continue to heat the mixture for
60-75 minutes. STIR constantly using the magnetic spin vane.
7. Remove the apparatus from the heating source, continue running water through the condenser and allow
the mixture to cool to room temperature.
8. When the mixture has cooled, take apart the apparatus and use clean forceps to remove the magnetic
spin vane.
9. Using a calibrated Pasteur pipet slowly add 1.0 mL of 5% aqueous sodium bicarbonate solution. Stir with a
microspatula until carbon dioxide evolution is no longer vigorous. (The sodium bicarbonate reacts with
both the acetic acid and the sulfuric acid to produce carbon dioxide.)
