Name: _________________
Date: _________________
Chemistry
Synthesizing Esters LAB
Introduction
Carboxylic acids are structurally like aldehydes (H –C=O) and ketones (R –C=O –R’) in that they contain
the carbonyl group (C=O). However, an important structural difference is that carboxylic acids contain a
hydroxyl group (–OH) attached to the carbonyl carbon. In turn, this functional group is called the
carboxyl group (HO–C=O). This combination gives the group an important characteristic: it behaves as
an acid.
As a family, carboxylic acids are weak acids, which ionize only slightly in water. As aqueous solutions,
typical carboxylic acids ionize to the extent of only 1% or less.
Carboxylic acids react with alcohols in the presence of a strong acid, such as sulfuric acid, to form
esters in a condensation reaction. This reaction is also known as esterification.
Ester formation is an equilibrium process. This means both reactants and products are present at some
concentration. For example, when 1 mol of acetic acid and 1 mol of ethyl alcohol are mixed, 0.677 mol of
the ester and 0.677 mol of water are produced, and 0.333 mol of acid
and 0.333 mol of alcohol remain.
The yield of an ester can be increased either by removing one of the
products of the reaction as it is formed, or by increasing the
concentration of one of the reactants. The normal procedure is to
remove water using the dehydrating agent sulfuric acid that also
acts as a catalyst.
A carboxylic acid does not react with an alcohol unless a strong acid,
such as sulfuric acid, is present as a catalyst. Protonation makes the
carboxyl group more electrophilic and enables it to react with the
alcohol which is a weak nucleophile.
A distinct difference between carboxylic acids and esters is in their
odors. Carboxylic acids are noted for their sour, disagreeable odours. On the other hand, esters typically
have sweet, very pleasant odours often associated with fruits. These compounds are used in the food
industry as flavoring agents. For example, while butyric acid gives rancid butter its putrid odor, the ester,
ethyl butyrate, is used as the artificial flavoring agent of pinneaple. In the lab, esters can be synthesized
from the condensation reaction between alcohols and carboxylic acids.
Purpose
To produce several esters and observe their odours.
Materials
●​ 2 x 500 mL beaker
●​ hot plate
●​ test tubes
●​ test tube rack
●​ test tube holder
●​ distilled water
●​ pipettes
●​ scoopula
●​ concentrated ethanoic acid (glacial acetic acid) , CH3COOH(l) (for teacher use only)
●​ concentrated sulfuric acid, H2SO4(aq) (for teacher use only)
●​ various alcohols and carboxylic acids
Procedure
1.​ Prepare a 60oC water-bath by filling a 500 mL beaker half-full with tap water. Heat the water until it
comes to a boil. Turn the heat off when the water starts to boil.
2.​ Prepare a 0oC cold-water bath by filling a 500 mL beaker half-full with tap water and adding ice
cubes to the cold water.
3.​ Label small test tubes and place them in a test tube rack.
4.​ First add 10 drops of liquid carboxylic acid to the test tube. If using salicylic acid, use a small
spatula full, about 0.08 g. Note the odours of the acids before reaction. Do not inhale any acid
directly – use the wafting method. Record your observations. You will add all acids yourself except
the ethanoic acid (glacial acetic acid), which your teacher will add for you.
5.​ Then add 10 drops of the corresponding alcohol. Note the odour of each alcohol before the reaction.
Do not inhale any alcohol directly – you will catch the odour of the alcohol by simply being around it.
Record your observations.
6.​ Under the fume hood, your teacher will carefully add 2 drops of concentrated sulfuric acid to each
test tube. Gently shake the test tubes to mix.
7.​ Place the test tubes in the warm water bath for 5-10 minutes without getting water into the tube.
8.​ Remove the test tubes and cool in the cold-water bath for about 5 min.
9.​ Pour contents into a clean beaker or leave in the test tube and add a few drops of distilled water if
necessary to note the odor of the ester formed. Note the odor of each product by fanning (wafting)
the vapours toward your nose. Record your observations. Clean and dry the watch glass with a
paper towel before adding the next ester to the watch glass.
10.​ The small quantities of esters prepared can be safely disposed of by flushing down the drain with
large quantities of water. Clean all glassware and wash your hands thoroughly with soap and water.
Note: Prepare all your esters at the same time.
Safety:
●​ Alcohols and organic acids are flammable! Do not use around open flames or other sources of
ignition.
●​ The acids are corrosive and can cause burns. Avoid skin and eye contact. If you spill these
chemicals on your skin, wash the affected area with a lot of cool water.
●​ The alcohols are toxic. Wash hands with soap and water after handling these chemicals.
●​ Use caution around the hot plate. Avoid touching the heating surface with your hands. To unplug the
hot plate, pull on the plug itself rather than the cord.
Observations
Sample table
Alcohol
Carboxylic Acid
Methanol
Salicylic Acid
Isopropyl
Ethanoic Acid
Ethanol
Ethanoic Acid
1-Octanol
Ethanoic Acid
Ester
Odour (Before and
After)
Possible Smells
Oil of wintergreen, Nail polish, Citrus/orange, Pear
Analysis
1.​ For each reaction include the:
a.​ chemical equation for the reaction
b.​ structural formulas for each molecule and
c.​ names of each molecule
2.​ How do you know that a new product was formed in each reaction?
3.​ Describe the odour of the ester produced in each reaction and compare this to the initial odour of the
reactants.
4.​ Explain why the synthesized ester does not always match the odour of the fragrance found in nature.
5.​ What is the function of concentrated sulfuric acid in the reactions? Describe its mechanism of
action.
6.​ Locate five different grocery items that contain esters. Form a table listing the food item, the ester(s)
found within, and then name the carboxylic acid and alcohol that would be derived from hydrolyzing
each ester.
Lab Write Up
Purpose specific (not general) 1 mark
Materials list only materials you actually used 1 mark
Procedure written in past tense; describes what you actually did; written in 3rd person (i.e. no I, we) 2
marks
Observations labelled table; include odours of reactants before reaction and odours of the products
after the reaction has proceeded 2 marks
Analysis answer q’s in paragraph format; include discussion of role of sulfuric acid
3 marks for chemical equation + 3 marks for structural formulas + 3 marks for names of each molecule
+ 3 marks for role of sulfuric acid (use the words dehydrating agent, catalyst, mechanism,** research
needed**) + 5 marks for table
Conclusion 1-2 sentances 2 marks