Name(s): ______
Signature(s): ______
ESTERS OF CARBOXYLIC ACIDS
BACKGROUND
Did you know that the aromas of bananas, strawberries, other fruits, flowers, and perfumes are the result of organic chemistry? Many of these flavor additives are esters. An ester is an organic compound that is produced when a carboxylic acid reacts with an alcohol. They are probably the most pleasant and delicious organic compounds one can study.
A functional group is a specific arrangement of atoms in an organic compound that is capable of characteristic chemical reactions. The chemistry of an organic compound is determined by its functional group. R is any carbon chain/ring attached to the functional group (in red). The general equation for this reaction is:
R1COOH + R2OH D R1COOR2 + H2O
carboxylic acid alcohol ester water
reactants products
The name of the ester formed is derived from the names of the alcohol and the carboxylic acid. For example, the ester formed from ethyl alcohol and acetic acid is called ethyl acetate. The first part of the name comes from the alcohol and the second part comes from the acid (Figure 1).
Figure 1: Ethyl Acetate
In this laboratory, you will synthesize and identify several esters. Sulfuric acid will be used as a catalyst for the esterification reactions.
OBJECTIVES: When you have completed this activity, you will be able to:
1. Describe the structure of an ester and how it is formed
2. Synthesize several esters
3. Research and describe how esters are used in society
…in order to illustrate the usefulness of organic compounds..
MATERIALS
alcohols / hot plateamyl (1-pentanol) / thermometer
methanol / beaker (400 mL)
carboxylic Acids / 2 Dropper Pipettes
glacial acetic acid / graduated Cylinders (10.0 mL)
salicylic acid (solid) / test tube rack
18 M sulfuric acid (concentrated) / 2 test tubes (16 x 100 mm)
(in fume hood) / test tube holder
distilled water / balance
china marker / weigh boat
timer
PROCEDURE
CAUTION: You will be working with concentrated acids.Wear goggles, lab aprons, and closed-toe shoes.
1. _____ Prepare a water bath by adding 175 mL of tap water to a 400 mL beaker. Place the beaker on a hot plate and heat the water until the temperature is between 50 - 60°C.
2. _____ Number 2 test tubes toward the top of the tube with a china marker. Into each of two numbered test tubes, put 20 drops of alcohol (1.0 mL) and 10 drops of carboxylic acid (0.5 mL). For salicylic acid, add 0.50 g of the carboxylic acid. See Table 1.
Table 1Test Tube / 1.0 mL Alcohol / 0.5 mL Carboxylic Acid
1 / amyl alcohol / glacial acetic acid
2 / methyl alcohol / salicylic acid (0.5g)
3. _____ Carefully add 2 - 3 drops of concentrated sulfuric acid (H2SO4) to each test tube.
CAUTION: Handle concentrated sulfuric acid carefully. If the acid spills onyour skin or clothing, immediately rinse the affected area with
water and inform your teacher.
4. _____ Stir each mixture slightly by tapping the bottom of the tube with your finger.
5. _____ Place the test tubes in the hot water bath (50 - 60°C) for 10 minutes. While you are waiting, complete “Structure of Hydrocarbons” attached.
6. _____ Using a test tube holder, remove the test tubes from the water bath and place them in a test tube rack.
7. _____ Add 5.0 mL of dI water to each test tube and mix. Esters are insoluble in water and appear as colorless liquid layers on top of the water.
8. _____ Immediately note the odor of the esters formed by wafting the fumes toward your nose with your hand. Try to relate each odor to a familiar, specific scent. Record your observations in the “Observations and Conclusions” Table.
DATA
Table 2: Observations and ConclusionsTest Tube / Alcohol / Carboxylic Acid / Ester formed / Odor
1 / amyl alcohol / glacial acetic acid / amyl acetate
2 / methyl alcohol / salicylic acid / methyl salicylate
ANALYSIS:
1. Below are the equations for each of the esterification reactions performed in this experiment. Use 1a as an example to complete the formula for the ester in questions 1b and 1c.
a. CH3OH + C6H13COOH D CH3COOC6H13 + H2O
methyl alcohol heptanoic acid methyl heptanoate water
b. C5H11OH + CH3COOH D ______COO______+ H2O
amyl alcohol acetic acid amyl acetate water
c. CH3OH + C6H4OHCOOH D ______COO______+ H2O
amyl alcohol salicylic acid methyl salicylate water
2. A banana scented candle could contain this additive ester:
a. Amyl acetate
b. Methyl salicylate
c. Methyl heptanoate
3. A wintergreen scented car freshener could contain this additive ester:
a. Amyl acetate
b. Methyl salicylate
c. Methyl heptanoate
4. An ester is formed by reacting:
a. alcohol with water
b. carboxylic acid with water
c. carboxylic acid with alcohol
5. The functional group for an alcohol is
a. R
b. –OH
c. H2O
d. –COOH
6. Amyl acetate is an inorganic compound.
a. True
b. False
7. Esterification is often classified as a dehydration reaction because…
a. water is produced in the reaction
b. water is used as a reactant in the reaction
8. Why was sulfuric acid added to the reaction?
a. To speed up the rate of the reaction
b. To keep the rate of reaction constant
c. To make the reaction more dangerous and exciting for chemistry students
d. To slow down the rate of the reaction so the ester could be smelled for longer periods of time
9. Esters are soluble in water.
a. True
b. False
10. According to the IUPAC naming system, the name of this hydrocarbon is:
a. Butane
b. Butene
c. Butyne
d. Propane
e. Propene
f. Propyne
Name: ______Date: ______Period: ______Page: ______
PRE-LAB: ESTERS OF CARBOXYLIC ACIDS
Read the introduction and procedure to the lab activity, highlighting key information as you read. Use the information in the introduction, procedure, and your class notes to answer the following questions.
1. Write the general formula for the reaction between a carboxylic acid and an alcohol. Identify each reactant and product.
2. Name the ester formed from each of the carboxylic acids and alcohols. For the alcohol, remove the –anol ending and replace it with –yl.
Alcohol / Carboxylic Acid / Esteroctanol / acetic acid / octyl acetate
propanol / butanoic acid
2 – pentanol / benzoic acid
ethanol / acetic acid
3. What safety precautions relate specifically to this lab?
4. What is the role of a catalyst in a reaction?
5. Why is water added to the test tubes after the esters are formed?
STRUCTURE OF HYDROCARBONS
Hydrocarbons are the simplest organic compounds that contain only carbon and hydrogen. The two simplest hydrocarbons are methane (CH4) and ethane (C2H6).
IUPAC Rules for naming straight chain hydrocarbons:
1. Find the longest chain of carbons.
2. Count how many carbons are in that longest chain and use the correct prefix
# carbons / example / prefix / # carbons / example / prefix1 / CH4 / meth- / 6 / C6H14 / hex-
2 / C2H6 / eth- / 7 / C7H16 / hept-
3 / C3H8 / prop- / 8 / C8H18 / oct-
4 / C4H10 / but- / 9 / C9H20 / non-
5 / C5H12 / pent- / 10 / C10H22 / dec-
3. The suffix reflects whether the hydrocarbon is an alkane, alkene, and alkyne.
-ane / only single covalent bonds-ene / One or more carbon-carbon double covalent bond
-yne / One or more carbon-carbon triple covalent bond
Name the following structures: Write the correct name in the box for each hydrocarbon
Options: butane, butene, ethane, ethyne, propane, propene, propyne
1./ 2.
/ 3 . / 4.
5. / 6.
/ 7.