Project Name: Esters
Submitted By: Nicolas Spagnolo
Overview
Humans can distinguish more than 10,000 different smells (odorants), which are detected by
specialized olfactory receptor neurons lining the nose.... It is thought that there are hundreds of
different olfactory receptors, each encoded by a different gene and each recognizing different
odorants.
Each of the hundreds of receptors are encoded by a specific gene. If your DNA is missing a gene or
if the gene is damaged, it can cause you to be unable to detect a certain smell. For example, some
people have no sense for the smell of camphor.
When you smell many fruits or flowers, what you are smelling is esters evaporating from the fruit or
flower. Esters are organic molecules. For example, the ester that gives a banana its smell is called
isoamyl acetate, and the formula for it is CH3COOC5H11. The primary smell of an orange comes
from octyl acetate, or CH3COOC8H17. Esters can now be made artificially, and that is where artificial
flavors come from.
Topic Area(s)
Chemistry:
Esters, lab
execution/mani
pulation
Age
10-13
senior
Cost
80 cents
per kid
Time
1 hour
Complexity
Preparation= 4/5
Execution= 4/5
Objective
The goal is to
form esters by
mixing a
carboxylic acid
with different
alcohols.
These esters
produce the
fruity smell that
is found in
fruits such as
bananas and
oranges!
Hook
We will be CREATING the exact same “smell” molecule in the lab that is found in fruit.
Necessary Background Information
Esters are chemical compounds derived formally from a carboxilic acid (H) and an alcohol (OH).
Esters are ubiquitous. Many naturally occurring fats and oils are the fatty acid esters of glycerol.
Many esters have distinctive fruit-like odors, which has led to their commonplace use in artificial
flavorings and fragrances. For example:
Flavour
Ester
Volume of
Acetic
Anhydride
Alcohol (2 mL)
Banana
Isoamyl acetate
2.2 mL
Isopentyl alcohol
Pear
Propyl acetate
3.2 mL
1-propanol
Orange
Octyl acetate
1.5 mL
1-octanol
Peach
Benzyl acetate
2.3 mL
Benzyl alcohol
Apple
Hexyl acetate
1.9 mL
1-hexanol
Fruity
Isopropyl acetate
3.1 mL
Isopropanol (2propanol)
Food and beverage manufacturers are thoroughly familiar with these esters and often use them as
additives to spruce up the flavor or odor of a dessert or beverage. Many times odors do not have a
natural basis, as is the case with the “juicy fruit” principle, isopentenyl acetate.
Flavor is a combination of taste, sensation and odor transmitted by receptors in the mouth (taste
buds) and nose (olfactory receptors). There are four different tastes (sweet, sour, salty, and bitter).
The perception of flavor, however, is not so simple. The human actually possesses 9000 taste
buds and odor plays a big role in the perception of taste.
Although the “fruity” tastes and odor of esters are pleasant, they are seldom used in
perfumes or scents that are applied to the body.
Banana smell: isoamyl acetate
Orange smell: octyl acetate
COOL FACT:
Skatole or 3-methylindole is a mildly toxic white crystalline organic compound belonging to the
indole family. It occurs naturally in feces (it is produced from tryptophan in the mammalian digestive
tract), and coal tar, and has a strong fecal odor. In low concentrations it has a flowery smell and is
found in several flowers and essential oils, including those of orange blossoms, jasmine, and
Ziziphus mauritiana. It is used as a fragrance and fixative in many perfumes and as an aroma
compound. Its name is derived from the Greek root skato- meaning "dung". Additionally it is used in
very small quantities as an artificial flavor and scent for strawberry flavored food products including
ice cream
Skatole:
Materials
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Kids will partner up in groups of 2
Two 1L beakers
4 dry test tubes per group (4 x 5 groups = 20 test tubes total)
2 ml of acetic anhydride per group ( 2 x 5 groups = 10 ml total)
2.2ml of isoamyl alcohol (banana) OR 1.5 ml of 1-octanol (orange) per group
20g of sodium chloride
20g of sodium bicarbonate
Two 150ml beakers per group (2 x 5 = 10 beakers total)
1 micropipette
1 test tube holder per group (1 x 5 = 5 total)
Safety Considerations
1. Be extremely careful when handling the acetic anhydride, it is very corrosive! That’s why
you will be using micropipettes!
2. Be extremely careful when handling the concentrated sulfuric acid, it is very corrosive!
That’s why we’re using a squeeze bottle to pour the drops in the test tube.
3. The ester smells we are making are present at a very high concentration. Try to avoid
sniffing directly from the test tube! This would overwhelm your olfactory sensing
mechanism. Instead, place a drop or two on a piece of paper using a pipette and gently
waft the delightful fragrance in the direction of your nose.
Procedure
ester chosen
isoamyl acetate
(banana)
n-octyl acetate
(orange)
volume of acetic anhydride (mL)
2.2
1.5
1. Poor water and ice in the first 1L beaker (fill to about 400ml mark).
2. Poor water in the second 1L beaker (up to about the 400ml mark) and heat up the beaker
using a hot plate. Try and maintain at about 70°C (do this while the kids are adding the
alcohol to the acetic anhydride→step 6).
3. Place the volume of acetic anhydride indicated in the above table in a dry test tube (1) using
a micropipette.
4. Add 3 drops of concentrated sulfuric acid and mix thoroughly.
5. Place 2.0 mL of one of the alcohols in a dry test tube (2).
6. Hold the test tube (1) containing the acetic anhydride in cold water (to cool the reaction), and
add the alcohol to it in several increments; mixing between additions. Without cooling, the
strongly exothermic reaction could become too vigorous.
7. Using the tongs, hold the tubes in hot water (at about 70ºC) for approximately 5 minutes to
complete the reaction.
8. Add eight drops of water using a Pasteur pipette. Mix briefly after each drop. The purpose is
to hydrolyze any excess unreacted acetic anhydride remaining after the etherification is
complete.
9. Cool the reaction mixture for 1 minute in 1L beaker of cold water.
10. Measure 6ml of distilled water using the measuring cylinder. Poor the water in a 100ml
beaker.
11. Add 20g of sodium chloride to the beaker to form a half saturated solution of NaCl.
12. Add this solution to the test tube (1) containing the acid and alcohol.
13. Mix thoroughly and vigorously. Then set the tube aside until upper and lower layers form.
The salt helps to break emulsions. If water alone were used, the two layers would not
separate easily. The upper layer is the ester, which is a water-insoluble volatile liquid. The
lower layer is a water solution of sulfuric and acetic acids.
14. Use a pipette to remove the top layer, and transfer it to another test tube (3).
15. Measure 6ml of distilled water using the measuring cylinder. Poor the water in a 100ml
beaker.
16. Add 20g of sodium bicarbonate to the beaker to form a half saturated solution of H2CO3.
17. Add this solution to the test tube (3) containing the ester.
18. Add 6.0 mL of saturated sodium bicarbonate to the upper layer in the test tube. Mix
vigorously and allow up to 5 minutes for the layers to separate. The base neutralizes
remaining acids (eq. 3 and 4), and helps to remove traces of acetic acid. Remove and
discard the lower layer. Retain the upper layer.
HCO3-(aq) + H+(aq) → H2CO3(aq)
H2CO3(aq) → H2O(l) + CO2(g)
19. Use a pipette to remove the top layer, and transfer it to another test tube (4).
20. This test tube (4) contains the ester, which results in the banana/orange smell. Investigate
the odor before storing the ester. Do not stick your nose nearly into the vial! This would
overwhelm your olfactory sensing mechanism. Instead, place a drop or two on a piece of
paper using a pipette and gently waft the delightful fragrance in the direction of your nose.
Let the kids guess what odor the think it is before letting them know the answer.
(3)
(4)