Making Scents of Estershandout2014

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Name_______________________
Making Scents of Esters
Introduction
In this investigation, you will produce esters through the condensation
reaction of an organic acid (an acid derived from a hydrocarbon) with an
alcohol. The esters you will produce should have familiar fragrances. Many
perfumes contain esters, and the characteristic aromas of many herbs and
fruits arise from the esters in the plants.
The functional groups of the acid and alcohol combine to form a water
molecule, while the remaining atoms join to form an ester molecule. This
process is called esterification. Using this chemical reaction, you will now
produce two esters. The esterification reaction is an example of a class of
reactions called condensation reactions because a small molecule (often
water) is formed as a by-product as the esterification occurs.
Before starting, read the procedure to learn what you will need to do, note
the safety precautions, and plan necessary data collecting and
observations.
1. Write the general structural formula for an organic acid (carboxylic acid):
2. Write the general structural formula for an alcohol:
3. Write the general structural formula for an ester:
General Esterification Reaction:
*R1OH + R2COOH  R2COOR1 + H2O
Specific Esterification Reaction:
CH3 OH + CH3COOH  CH3COOCH3 + H2O
Methanol + ethanoic acid  methyl ethanoate + water IUPAC names
(methyl alcohol + acetic acid  methyl acetate + water) common names
*R1 , R2, represent alkyl groups such as methyl, ethyl, etc.
Like many organic reactions, esterification typically requires a catalyst to
achieve reasonable rates of reaction at convenient temperatures.
Concentrated sulfuric acid (18M H2SO4) is the catalyst commonly employed
for this reaction. 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. In this lab,
the instructor will add the catalyst to your reaction when you are ready. We
will be limiting the size of the reactions to limit the amount of chemical
waste created.
Naming Esters
The name of an ester is derived from the alcohol and the organic acid that
are used to prepare it. The first part of the ester name comes from the
alcohol, and the second part of the name comes from the organic acid. For
example methanol and propanoic acid would produce methyl propanoate.
1-butanol and ethanoic acid (acetic acid) produce butyl ethanoate (aka
butyl acetate). Interestingly, when writing the structural formula for an
ester, the acid portion is typically written first, with the alcohol portion
appearing at the end, even though the first part of the name comes from
the alcohol.
When organic acids (aka carboxylic acids) are esterified (combined with an
alcohol to form an ester), the resulting esters are often 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.
Record your observations in the data table provided.
Materials:
2 small test tubes glass rod test tube holder goggles
apron
2 alcohol/organic acids pairs
Hot water bath
concentrated sulfuric acid (18M H2SO4) will be added by your teacher
Procedure
1. Hot water baths will be used to heat the reaction mixtures. Sharing
will be necessary. Play nice!
Reaction 1
2. Add 10 drops isopentanol (IUPAC name is 3-methyl-1-butanol) to a clean,
dry test tube. Note the odor of the alcohol. (Waft gently, don’t snort!)
3. Add 15 drops acetic acid. Note its distinctive odor. (Waft gently!)
4. Take the tube to the teacher to get the sulfuric acid catalyst added.
5. Use a test tube holder to keep the tube in the hot water bath for about
five minutes.
6. Insert the glass rod into the mixture and waft it near your nose. Do you
recognize the odor?
Reaction 2
1 Add 0.5g salicylic acid to a clean, dry test tube.
2. Add 20 drops methyl alcohol. Gently swirl the test tube to help the
salicylic acid to go into solution.
3. Take the tube to the teacher to get the sulfuric acid catalyst added.
4. Use a test tube holder to keep the tube in the hot water bath for about
five minutes.
5. Insert the glass rod into the mixture and waft it near your nose. Do you
recognize the odor?
Table 1: Alcohol/Carboxylic Acid Pairs and Resulting Esters
Reaction Name of
Name of
number Alcohol used Organic Acid
1
2
Name of Ester
produced
Scent of
ester
Questions:
1. Write the chemical reactions for each of the esters produced in the
above procedures.
Reaction 1
Reaction 2
2. isopentyl alcohol, 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?
___________________________
1. The esters produced in this laboratory experiment contain what
functional group characteristic of all esters?
_____________________________
5. What is the role of the sulfuric acid in these reactions?
_______________________________________________________
Ethyl butanoate is an organic compound that contributes to the odor of
pineapple.
6. Write the structural formula and the name for the alcohol used to make
ethyl butanoate.
7. Write the structural formula and name of the organic acid used to make
ethyl butanoate.
8) Identify the type of organic reaction that produces the compound that
contributes to the odor of pineapple. _______________________________
9) What is the byproduct produced in this reaction?_________________
Bonus: Write the structural, molecular and empirical formulas for ethyl
butanoate
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