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This Lab Stinks!
SCH 4UI – Ester Synthesis Lab
When a carboxylic acid (R – COOH) and an alcohol (R – OH) are mixed together and heated in the presence
of an acid catalyst (such as concentrated H2SO4), the two will react to form an ester (plus H2O) in a
condensation reaction. This process is called esterification.
R–C=O + HO–R'  R–C=O + HOH
|
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OH
O–R'
acetic acid = ethanoic acid or vinegar
acetate = ethanoate
Esters are known for their uses as artificial scents and flavours. Each ester has its own unique odour, and with
a discriminating nose, one can use this fact to help identify them. A list with the names of esters with their
scents will be available after the lab is completed.In this lab you will be reacting various organic acids (acetic
acid & salicylic acid) with various alcohols (methanol, isopentanol, 1-propanol & ethanol)You make at least
three different ester with odours that should be familiar to you.
Materials:
Goggles, apron, test tube rack, 6 test tubes, large beaker (600 mL or larger), hot plate, eye droppers, test tube
holders (3), gloves, small beaker of 5% sodium bicarbonate (NaHCO3) solution, concentrated sulfuric acid
(H2SO4), alcohols (methanol, ethanol, 1-propanol, butanol, 1-octanol), carboxylic acids (glacial acetic acid
(ethanoic acid), butanoic acid, formic acid (methanoic acid), salicylic acid)
Procedure:
Remember: GOGGLES MUST BE WORN AT ALL TIMES!
1.
2.
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4.
5.
6.
7.
8.
9.
Get 6 test tubes and label them: “1”, “2”, ‘3” etc.
Refer to the chart on the reverse side of the page. One at a time, add the contents listed for each tube.
Mix the contents of each test tube using the knocking method.
Obtain a large beaker of hot water. Water temperature should be between 50°C and 60°C.
Place all 6 test tubes together in the hot water bath for approximately 3 minutes.
Carefully remove the test tubes from the hot water and place them in the test tube rack.
Not ethe odour of each ester by wafting the vapours toward your nose, one at a time. Knocking the
test tube before wafting helps!)
You may wish to add a few drops of 5% sodium bicarbonate (NaHCO3) solution to a mixture if the
smell is not obvious. This will react with an unreacted acid and allow the scent of the ester to be more
obvious. (Caution – this reaction will be accompanied by fizzing and popping)
Empty out your test tubes into the waste container and place the test tubes inside the soaking bin.
Analysis and Discussion
1) Why do you think that that you were instructed to use an electric hot plate instead of a Bunsen
burner?
2) Why do you think that you were instructed to waft the odours instead of sniffing them directly?
3) Complete the observation chart to indicate the IUPAC name of each ester formed and the odour
associated with it.
4) What role does the H2SO4 play? How does it affect the esterification reaction?
5) Use structural diagrams to write each of the esterification reactions.
6) What evidence is there that the carboxylic acids used in this investigation are soluble or insoluble in
aqueous solution? Explain this in terms of the molecular structure of acids.
7) What evidence is there that the esters synthesized in this investigation are soluble or insoluble in
aqueous solution? Explain this in terms of the molecular structure of esters.
8) Evaluate the effectiveness of each reaction – were the odours recognizable? Was the use of sodium
bicarbonate effective
9) Aspirin is acetylsalicylic acid (A.S.A.) – a type of ester. Since acetyl is known as ethyl in IUPAC
nomenclature, suggest how this ester is formed by writing a reaction using structural diagrams. (A
picture of salicylic acid is drawn below). If time permits synthesize aspirin.
Salicylic acid
Safety Precautions:
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concentrated sulfuric acid is a strong oxidizing agent. It will start a fire if mixed incorrectly with any
of the alcohol or other acids used in this experiment. Use exactly as directed. Concentrated sulfuric
acid is also strongly corrosive (always wear goggles).
All of the liquid acids are corrosive – gloves are recommended.
Detect odours with caution. Breathing some of these vapours can cause dizziness, headache and
drowsiness. Waft the odours. Do not breathe deeply!
All alcohols and organic acids used in this experiment are flammable. Keep these materials away
from flames and other heat sources. (Formic Acid is particularly flammable – use with the utmost
caution)
Name: ______________________________
Partners: __________________________________________
Date: ____________________
Observation Chart
Tube
carboxylic acid
alcohol
1
1 scoop (1g) salicylic
acid
10 drops acetic acid
15 drops methanol
2
3
4
5
6
7
8
9
10 drops
12M H2SO4
10 drops isopentanol
10 drops
(isoamyl alcohol)
12M H2SO4
10 drops acetic acid
10 drops of ethanol
10 drops
12M H2SO4
10 drops butanoic acid
10 drops methanol
10 drops
12M H2SO4
10 drops acetic acid 10 drops of 1-propanol
10 drops
(n-propyl alcohol)
12M H2SO4
10 drops butanoic acid
10 drops of ethanol
10 drops
12M H2SO4
10 drops acetic acid
10 drops of 1-octanol
10 drops
(octyl alcohol)
12M H2SO4
10 drops acetic acid
10 drops of 1-butanol
10 drops
(n-butyl alcohol)
12M H2SO4
10 drops formic acid
10 drops of ethanol
10 drops
12M H2SO4
10
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catalyst
name of ester
produced
Methyl salicylate
Isopentyl
ethanoate
Ethyl ethanoate
Methyl butanoate
Propyl ethanoate
wintergreen
Pear, banana
(weak smell)
Nail polish remover,
model glue
Pineapple, apple,
strawberry
pear
Ethyl butanoate
Banana, pineapple,
strawberry
Octyl ethanoate
Fruity orange
Butyl ethanoate
Ethyl methanoate
Aspirin
try synthesizing the last 4 esters if time remains in class.
odour
Lemon, rum,
strawberry