CH243: Lab 4 Synthesis of Artificial Flavorings
by Fischer Esterification
PURPOSE:
To prepare esters by reaction of carboxylic acids and alcohols.
To modify a known procedure to prepare an unknown.
DISCUSSION:
Volatile esters usually have pleasant, fruity odors. The characteristic fragrance and flavor
of fruits and flowers are due, in most cases, to mixtures of esters. The mixture of esters
responsible for a natural flavor is usually complex and difficult to duplicate. However, if
the flavor is attributed to a major component then a synthetic ester of the same structure
can be substituted for the natural flavor at a fraction of the cost. For this reason, esters
are used in the food, flavor, and fragrance industries.
A formula for artificial pineapple flavor is given below. The composition of the mixture
is very important to duplicating the flavor; and it should also be pointed out that our
perceptions of an ester’s smell may depend on its dilution.
ARTIFICIAL PINEAPPLE FLAVOR
Pure Compounds
allyl caproate
isoamyl acetate
isoamyl isovalerate
ethyl acetate
ethyl crotonate
ethyl butyrate
terpinyl propionate
caproic acid
butyric acid
acetic acid
%
5
3
3
15
5
22
3
8
12
_5
81
Essential Oils
oil of sweet birch
oil of spruce
balsam Peru
volatile mustard oil
oil cognac
concentrated orange oil
distilled oil of lime
%
1
2
4
1
5
4
2
__
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Many esters can be conveniently prepared by refluxing a mixture of a carboxylic acid and
an alcohol in the presence of a strong mineral acid such as sulfuric acid or hydrochloric
acid. This reaction is shown by the following equilibrium equation:
O
O
R C OH
+
HO R'
H+
R C O R'
+
H2O
The acid catalyst increases the rate at which equilibrium is reached but does not affect the
position of the equilibrium. In order to shift the equilibrium to the right and prepare the
ester in reasonable yield two measures can be taken:
1) use a large excess of the alcohol, or
2) remove either the water or ester as it is formed.
The most common method of the two, especially when the alcohol is inexpensive as is
the case for methanol and ethanol, is to use an excess of the alcohol. This procedure is
call Fischer Esterification.
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The structures and approximate smell of a few esters follow:
Name
isoamyl acetate
Flavor
banana
Structure
O
CH3
methyl butyrate
CH3
C O CH2CH2CHCH3
apple
O
CH3CH2CH2
n-propyl acetate
pear
O
CH3
isobutyl propionate
C O CH2CH2CH3
rum
O
CH3CH2
ethyl butyrate
CH3
C O CH2CHCH3
pineapple
O
CH3CH2CH2
octyl acetate
C O CH3
oranges
C O CH2CH3
O
CH3
C O CH2(CH2)6CH3
INSTRUCTION:
In this experiment you are to synthesize an ester of your choice pretending that it has
never before been made. A common practice in frontier organic synthesis is to model
procedures for the preparation of a new compound after the procedures of a similar
reaction.
There are many sources for reaction procedures from which you can model your
synthesis. Following are known procedures for preparation of two common esters. Your
task is to synthesize one of a variety of esters by adapting one of these or another Fischer
Esterification procedures to fit your own reaction. For starters determine the molar
proportions you want to use in your reaction by modeling after those in the known
procedures.
The procedures given require refluxing. The advantage to refluxing is that a constant
temperature is maintained in the flask and the reaction can reach equilibrium without any
materials escaping at the higher temperature of the medium.
As this is hypothetically a frontier synthesis of an ester having never before been made
you will want to:

Keep appropriate records of your research in your lab notebook.

Characterize your product by using mp/bp, properties IR, NMR etc. as needed.


Analyze the cost effectiveness of your reaction.
Analyze the “greenness” of your synthesis using atom economy and comparative
data as learned in previous experiments.
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SAMPLE PROCEDURES:
1. Isoamyl acetate (banana)
O
CH3
C OH
CH3
+
HO
O
H+
CH2CH2CHCH3
CH3
CH3
C O CH2CH2CHCH3
+
H2O
1. Mix 6 mL of isoamyl alcohol and 10 mL of glacial acetic acid in a 100 mL round bottom
flask. Carefully add 1 mL of concentrated sulfuric acid while swirling.
2. Add either boiling chips or a stirring bar and assemble the apparatus for reflux. Gently
reflux with stirring for 30 minutes.
3. Allow the flask to then cool at room temperature for about five minutes and then cool in
an ice bath.
4. Pour the mixture into a separatory funnel and add 10 mL of cold water (made from ice
and distilled water chilled in an ice bath). Shake the layers and allow them to separate.
Remove and discard the lower, aqueous layer but keep the top organic layer.
5. Add another 10 mL portion of cold water to the organic oil, shake the layers and separate
them again. Discard the aqueous layer but keep the top organic layer.
6. Wash the organic layer with 10 mLs of saturated sodium bicarbonate (NaHCO3),
separate, and then wash once with it with 10 mLs of saturated sodium chloride solution
(NaCl).
7. Transfer the organic layer to a 125 mL Erlenmeyer flask and dry it for five minutes over
magnesium sulfate (MgSO4). Filter the dried solution.
8. Determine the weight of your crude product. If so instructed purify the banana oil by
simple distillation.
9. Calculate the yield, the % yield, and put the sample in a labeled vial to turn in.
2. n-Propyl acetate (pear)
O
CH3
O
C OH +
HO CH2CH2CH3
H+
CH3
C O CH2CH2CH3
+
H2O
1-3.
Use the above recipe for banana flavor but use 8 mLs of 1-propanol instead of the
isoamyl alcohol. Use the same amounts of the other reagents.
4-6.
Instead of washing with water, use 15 mL portions of saturated sodium chloride and
then three 10 mL portions of saturated sodium bicarbonate, and finally again with 10
mL sodium chloride.
7-9.
Same as above.
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Lab 4: Synthesis of Esters
Name__________
Prelab Questions:
1. On the back write out the step by step mechanism for formation of your ester. Include action
of the catalyst.
2. A. What is the purpose for the saturated sodium bicarbonate in the purification steps? (be
specific)
B. Write the reactions of sodium bicarbonate with components of the product mixture.
3. A. Why do some procedures have you wash your product with a saturated sodium chloride
solution? Explain what it is doing?
B. Why do some procedures have you add anhydrous sodium sulfate or anhydrous
magnesium sulfate to your product before distillation? Explain what these are doing?
4. Some esters can be isolated by distillation directly from the reaction mixture but some
isolation of some esters require neutralization and extractions prior to purification by
distillation. Explain why?
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Lab 4: Synthesis of Esters
Name__________
Postlab Questions:
1. Analyze the cost effectiveness of your reaction.
 Make a table of costs of reagents
 Determine the $ per mL or g of product produced.
2. Analyze the “greenness” of your synthesis using atom economy and comparative data as
learned in previous experiments.
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