Download Making Scents of Esters

Making Scents of Esters
Introduction:
An ester is an organic compound that is formed, in addition to water, when a
carboxylic acid reacts with an alcohol. This process is called esterification.
General Reaction:
Specific Reaction:
Esterification typically requires a catalyst to speed it, and for decades,
concentrated sulfuric acid (18M H2SO4) has been used to do so. Sulfuric acid is a very
dangerous chemical, which can cause severe chemical burns when in contact with skin,
and therefore, the utmost care should be taken when working with sulfuric acid.
When carboxylic acids are esterified (combined with an alcohol to form an ester),
the resulting esters are liquids with fruity flavors. These synthetic esters are used in the
food industry as flavorings. In many cases, the synthetic esters produced in the
laboratory are nearly the same molecules that give fruits their characteristic flavors.
Materials:
4 small test tubes
400-mL beaker
4 125-mL Erlenmeyer flasks
hot plate
test tube holder
goggles
apron
4 alcohol/carboxylic acids pairs
concentrated sulfuric acid (18M H2SO4)
Procedure:
*Record all data in the attached data table.
1. Add about 200 mL water to the 400-mL beaker. Heat the water until it boils
and then turn off the hot plate.
2. Add 10 drops iosamyl alcohol to a clean, dry test tube. Label the test tube
“1.”
3. Add 10 drops octyl alcohol to a second clean, dry test tube. Label the test
tube “2.”
4. Add 20 drops methyl alcohol to a third clean, dry test tube. Label the test tube
“3.”
5. Add 10 drops propyl alcohol to a fourth clean, dry test tube. Label the test
tube “4.”
6. To test tubes 1, 2, and 4, add 30 drops acetic acid.
7. To test tube 3, add 0.5g salicylic acid. Gently swirl the test tube to ensure the
salicylic acid to go into solution.
8. Add 2 drops of the concentrated sulfuric acid to each of the 4 test tubes.
9. Using a test tube holder, place the test tubes into the beaker of near-boiling
water. Let the test tubes stand in the hot-water bath for 5 minutes.
10. Label the 125-mL Erlenmeyer flasks “1,” “2,” “3,” and “4.” Add water to
each until it is about 1/3 full.
11. Pour the contents of the test tubes into the correctly labeled flask and swirl.
12. Carefully smell the ester by waving a hand across the mouth of the flask to
push the vapor toward your nose. Describe the odor of the sample in the table
below.
13. Rinse the contents of the flasks down the drain with water.
Table 1: Alcohol/Carboxylic Acid Pairs and Resulting Esters
Test
Carboxylic
Tube
Alcohol
Amount
Acid
Amount
Ester
Produced
Odor of
Ester
1
2
3
4
Questions:
1. Write the chemical reactions for each of the esters produced in the above
procedures.
2. Isoamyl alcohol, octanol, methanol, and propanol contain what functional group
characteristic of all alcohols?
3. Acetic acid and salicylic acid contain what functional group characteristic of all
carboxylic acids?
4. The esters produced in this laboratory experiment contain what functional group
characteristic of all ester?
5. Isobutyl alcohol and formic acid combine to produce a raspberry odor. Predict
the name of the ester.
Organic Structures:
Alcohols:
HO
OH
isoamyl alcohol
methanol
(or methyl alcohol)
HO
HO
propanol
octanol
(or octyl alcohol)
(or propyl alcohol)
Carboxylic Acids:
HO
HO
HO
O
O
salicylic acid
acetic acid
Esters:
HO
O
O
O
O
methyl salicylate
isoamyl acetate
O
O
octyl acetate
O
O
propyl acetate