Synthesis of Fragrant Esters
Introduction:
An ester is an organic compound that is formed when a carboxylic acid reacts with an
alcohol. In addition to an ester being form, water is another product of the reactions.
Esterification typically requires a catalyst to speed the reaction. For years concentrated
sulfuric acid (H2SO4) has been used to do so. Sulfuric acid is a very dangerous chemical,
which can cause severe chemical burns when in contact with all human tissues. The
utmost care needs to be taken when working with sulfuric acid.
When carboxylic acids are esterified (combined with an alcohol to form an ester), some
of the resulting esters are liquids with fruity scents or flavors. These synthetic esters
produced in the laboratory are nearly the same molecules that give fruits their
characteristic flavors.
Materials
Various Alcohols:
Various Organic Acids:
Test tubes (5-8)
Hot Plate
Gloves
Goggles
Pipets
Stiring rods
Part A: Synthesis of The Oil of Wintergreen
Methylsalicylate (oil of wintergreen) is an ester in which the carboxyl group of salicylic
acid has reacted with the alcohol group of methyl alcohol. Oil of wintergreen is used
both as a topical analgesic in rubs for sore muscle and a flavoring agent.
Carboxylic Acid
salicyclic acid
Anthranilic Acid
Alcohol
Methanol (Methyl Alcohol)
Methanol (Methyl Alcohol)
Ester
methyl salicylate
methyl anthranilate
Fragrance
Wintergreen
Grape
Procedure
1. Place 0.2 grams of salicylic acid into a clean, dry 10-cm test tube.
2. Add 6 drops of methyl alcohol and agitate the tube until the contents are well mixed.
3. Then add 1 drop of concentrated sulfuric acid.
SAFETY ALERT: Remember to use concentrated sulfuric acid with care and wash
off any contacted area with cool water.
4. Agitate the tube contents and place the tube in a beaker of boiling water for three
minutes.
5. After heating is complete remove the tube from the bath and add 15 drops of water to
the tube contents.
6. Cautiously note the odor of the products in the test tube by wafting the scent to your
nose. Do this until you can detect an odor. Record the odor.
Part B: Synthesis of Grape
1. Place 0.2 grams of anthranilic acid into a clean, dry 10-cm test tube.
2. Add 6 drops of methyl alcohol and agitate the tube until the contents are well mixed.
3. Then add 1 drop of concentrated sulfuric acid.
SAFETY ALERT: Remember to use concentrated sulfuric acid with care and wash
off any contacted area with cool water.
4. Agitate the tube contents and place the tube in a beaker of boiling water for three
minutes.
5. After heating is complete remove the tube from the bath and add 15 drops of water to
the tube contents.
6. Cautiously note the odor of the products in the test tube by wafting the scent to your
nose. Do this until you can detect an odor. Record the odor.
Part C: Synthesis of Pear, Banana, and Orange
A number of other commercially important esters can also be synthesized using a similar
procedure that yielded oil of wintergreen.
In this experiment, you will synthesize three esters used commercially as flavorings,
using acetic acid.
Carboxylic Acid
Acetic acid
Acetic acid
Acetic Acid
Alcohol
n-propyl
Isoamyl
Octyl alcohol
Ester
n-propyl acetate
Isoamyl acetate
n-octyl acetate
Fragrance
Pear
Banana
Orange
Procedure
1. Prepare n-propyl acetate by putting 6 drops on n-propyl alcohol in a clean, dry 10-cm
test tube.
2. Add 2 drops of glacial acetic acid.
3. Add 1 drop of concentrated sulfuric acid, agitate the tube to mix the contents, and
place the test tube in boiling water bath for 3 minutes.
SAFETY ALERT: Remember to use concentrated sulfuric acid with care and wash
off any contacted area with cool water. Both glacial acetic acid and concentrated
sulfuric acid will vigorously attack tissue. Avoid contact and wash any contacted
area immediately with large amounts of cool water.
4. When heating is completed, remove the test tube from the bath, and add 20 drops of
water to the test tube contents. Agitate to mix.
5 Cautiously note the odor of the product, using the method described in step 6 of the
procedure for the oil of wintergreen (Part A). Record the odor in the data table.
6. Repeat Steps 1 to 5 twice using the following pairs of alcohols and acid: isoamyl
alcohol plus glacial acetic acid, and octyl alcohol plus glacial acetic acid.
7. Note and record the odor of the produced esters. Do not worry about having the
“correct” odor for a particular ester. Descriptions of odors often vary with people, and
some odors hard to describe.
Part D: Synthesis of Pineapple, Strawberry and Apple
Although the procedure for the following ester is much the same as in Part C, special
attention must be paid when using butyric acid. The use of a fume hood is necessary
because of butyric acid strong unpleasant odor.
Carboxylic Acid
Butyric Acid
Butyric Acid
Butyric Acid
Alcohol
n-butyl
Ethyl
Methanol (Methyl Alcohol)
Ester
n-butyl butyrate
ethyl butyrate
methyl butyrate
Fragrance
Pineapple
Strawberry
Apple
Procedure
1. Prepare n-butyl butyrate by putting 6 drops of n-butyl alcohol in a clean, dry 10-cm
test tube.
2. Wearing chemically resistant gloves to avoid contact with skin, add 2 drops of butyric
acid.
3. Add 1 drop of concentrated sulfuric acid, agitate the tube to mix the contents, and
place the test tube in boiling water bath for 3 minutes.
SAFETY ALERT: Remember to use concentrated sulfuric acid with care and wash
off any contacted area with cool water. Concentrated sulfuric acid will vigorously
attack tissue. Avoid contact and wash any contacted area immediately with large
amounts of cool water.
4. When heating is completed, remove the test tube from the bath, and add 20 drops of
water to the test tube contents. Agitate to mix.
5 Cautiously note the odor of the product, using the method described in step 6 of the
procedure for the oil of wintergreen (Part A). Record the odor in the data table.
6. Repeat Steps 1 to 5 twice using the following pairs of alcohols and acid: ethyl alcohol
plus butyric acid, and methyl alcohol plus butyric acid.
7. Note and record the odor of the produced esters. Do not worry about having the
“correct” odor for a particular ester. Descriptions of odors often vary with people, and
some odors hard to describe.
Data
Acid and Alcohol Reacted
Product Odor
Salicyclic Acid and Methyl Alcohol
Anthranilic Acid and Methyl Alcohol
Acetic Acid and n-Propyl Alcohol
Acetic Acid and Isoamyl Alcohol
Acetic Acid and Octyl Alcohol
Butyric Acid and n-Butyl Alcohol
Butyric Acid and Ethyl Alcohol
Butyric Acid and Methyl Alcohol
____________
____________
____________
____________
____________
____________
____________
____________
Questions
1. What role does sulfuric acid play in the production of the esters in lab?
2. Name three commercial products that contain oil of wintergreen.
i.
ii.
iii.
3. What is the difference between artificial Flavoring and natural flavoring?
4. Explain how the esters made in this lab could or could not be used in the following:
a. Coloring agents
b. Flavoring agents
c. Analgesics