Download Pre-AP Chemistry

Pre-AP Chemistry
Instructor: Mr. Malasky
Name ___________________________________ Period _________ Due Date _____________
Laboratory Activity: Esters and the Flavor Industry
Many foods and consumer products contain artificial flavors as additives. Many of these
flavors are organic molecules called esters that are synthesized in the lab. Chemists discovered
about two hundred years ago that these compounds could be produced when an alcohol was
reacted with an organic acid. The esters have wide applications as fragrances and flavors in many
foods, beverages, and household consumer products. The general equation for this reaction is:
organic acid + alcohol  ester + H2O
A food technologist may utilize a natural ester or a mixture of natural and artificial esters
to produce a flavor or fragrance. In some cases, an artificial ester may not duplicate a natural
ester, but most people cannot tell the difference. Only a trained taster can generally tell the
difference between a natural and artificial ester. Many alcohols and organic acids are known for
their pungent and nauseating odors, yet the reaction of the two creates a pleasing odor. Usually
only cheap perfumes use esters, while more expensive ones use natural essential oils that are
extracted by alcohol. Esters are not stable to perspiration and usually break down producing the
carboxylic acid, generally with an unpleasant odor.
Esters are named by first giving the alcohol name, followed by the acid name with the
suffix changed from –ic to –ate. For example, ethyl alcohol and acetic acid produce ethyl acetate.
In completing these reactions, sulfuric acid is also used, serving as a dehydrating agent. If water
molecules are removed from the products, the reaction to produce esters favors making more
ester. This situation is a principle of equilibrium because the reaction is reversible.
Materials
hot water bath- hot plate with 250 ml beaker ½ full of boiling water
test tubes w/rack
ethyl alcohol
butyric acid
amyl alcohol
isobutyl alcohol
acetic acid (glacial)
octyl alcohol
test tube holder
formic acid
methyl alcohol
deionized water
6 M H2SO4
Methods: Carry out each reaction noted by completing the test tube combinations shown in the
chart based on drops of each reactant, adding the sulfuric acid last. Heat each tube in a deionized
boiling water bath for 5-10 minutes, maintaining at least ½ beaker of water at all times. For
results, describe odors produced using at least three descriptors, then conclude about the flavor
produced. *Butyric acid addition should be done under the fume hood.
Tube
1
2
3
Alcohol/drops
Amyl/ 14
Octyl/ 15
Methyl/ 14
over-------
Acid/drops
Acetic/ 15
Acetic/ 11
*Butyric/ 16
H2SO4 dps
8
8
8
4
5
6
7
Ethyl/ 15
Ethyl/ 15
Amyl/ 20
Isobutyl/ 15
*Butyric/ 12
Formic/ 9
*Butyric/ 9
Formic/ 10
8
8
8
8
Observations (70 pts)
Tube
1
Descriptors
Flavor
2
3
4
5
6
7
Questions (30 pts)
1. What is the chemical name of the ester formed in tube #1?
2. Why is a hot water bath used instead of directly heating with the burner?
3. Name three specific consumer products (brand and flavors) that contain esters.
4. How might the reaction differ without the addition of sulfuric acid?
5. What is the most obvious evidence of chemical change in all of these reactions?