[Chemical Engineering Laboratory 1]

Preparation of Aspirin and Oil of Wintergreen

Candidate’s Name : SAM KAR YEN

Student ID : SCM - 027837

Group Member’s Name : NG LIANG AIKKOW JING YANGFONG KAH WEITAN YEN BINGTAI SIM YEEBRENDA CHOO MUN JENGLIM SIN NIETAN WOAN GIUNRONALD SELVAMOLIVER PRASATH

Lecturer/ Supervisor : DR WONG VOON LOONG

Date of Submission : 13th MARCH 2015

1. ABSTRACT

In this laboratory experiment, acetylsalicylic acid and methyl salicylate was synthesised.

Acetylsalicylic acid is commonly known as aspirin while methyl salicylate as oil of wintergreen.

To synthesis aspirin, acetic anhydride and five drops of concentrated sulphuric acid was added to

salicylic acid. Sulphuric acid acts as a catalyst to increase the rate of reaction by lowering the

activation energy. Suction filtration is performed to separate the residue. The residue was washed

for several times as acetic anhydride is decomposed by the addition of water for the formation of

aspirin. Formed aspirin is allowed to air dry. To synthesis oil of wintergreen, salicylic acid was

mixed with methyl alcohol. Three drops of concentrated sulphuric acid was added as a catalyst to

speed up the reaction. The odour released was noted before and after heating. Finally, both the

products collected were tested with 1% of iron (III) chloride, all the changes were recorded.

Through this experiment, we can know that two different esters compound can be synthesised by

the same chemical which is salicylic acid.

2. INTRODUCTION

Organic compound synthesis and uses are very important section is this modern world.

Acetylsalicylic acid and methyl salicylate are both an ester. An ester compound can be formed

by reaction of a carboxylic acid (compound containing –COOH group) and an alcohol

(compound containing an –OH group). The reaction is termed as esterification. Esters basically

have strong and pleasant scents, such as odour of strawberries and mint. In this way, many esters

will be used as flavourings and perfume agents, as well as ointments for the relief of muscle

pain.

2.1 Acetylsalicylic acid

Acetylsalicylic acid also known as aspirin, has the potentiality as an analgesic to reduce minor

pains, as an anti-inflammatory medication to reduce redness and as an antipyretic to reduce

fever. Theoretically, aspirin can be synthesised by heating salicylic acid and acetic acid for a

certain period of time. However, to accomplish the esterification more quickly, acetic anhydride

was used instead of acetic acid in this experiment. It is because acetic anhydride is more reactive.

2.2 Methyl salicylate

Methyl salicylate has a common name as oil of wintergreen. Methyl salicylate will release a

pleasant minty scents. Methyl salicylate is used as a flavouring agent and the in rubbing

liniments that can relief the muscle cramping because it can penetrate through skin. It is prepared

by esterification of the carboxylic acid group (-COOH), of salicylic acid with methyl alcohol.

Phenol is a compound in which the hydroxyl group (-OH) attached to a phenyl ring (-C6H5). This

compound presents in both salicylic acid and methyl salicylate but not in acetylsalicylic acid.

Most of the phenols will form coloured complexes with iron (III) chloride, FeCl3. Thus, 1%

FeCl3 solution is added to test for the presence of phenol. The colours range from green through

blue and red through violet.

Acetic acidAcetylsalicylicacid

Acetic anhydrideSalicylic acid

Methyl salicylateMethyl alcoholSalicylic acid

3. Experimental Method

3.1 Objectives

To synthesis acetylsalicylic acid

To synthesis methyl salicylate

To review the phenol function group reacts with iron(III) chloride.

3.2 Apparatus

125ml Erlenmeyer Flask

10ml graduated cylinder

Filter paper

600ml beaker

Large test tube

Water bath

3.3 Chemical

Acetic anhydride

1% iron(III) chloride solution, FeCl3

Salicylic acid

Ice

Absolute ethanol

Methyl alcohol

Concentrated sulphuric acid, H2SO4

Distilled water

3.4 Cautions

If acetic anhydride and concentrated H2SO4 come in contact with skin, can cause severe

burns. Immediately wash the area with large amount of water if you get any of these

reagents on you.

Instead of disposing any chemicals down the sink, use the waste containers provided.

3.5 Procedure

(i) Synthesis of Aspirin

Add 3g of salicylic acid in a 125ml Erlenmeyer flask

Add 6ml of acetic anhydride and 5 drops of concentrated H2SO4

Mix the reagent by swirling the flask

Place the flask in 80oC of water bath for 20 minutes

Cool down to room temperature

Add 40ml of distilled water to the mixture.

Cool the mixture in ice bath

Filter the crystals and wash with water

Allow the crystal to air dry

Obtain and record the mass of crystal.

(ii) Synthesis of Oil of Wintergreen

Place 1g of salicylic acid and 5ml of methyl alcohol in large test tube

Add 3 drops of concentrated H2SO4

Place the test tube in 70oC of water bath for 15 minutes

Note the odour

Add a drop of 1% FeCl3

Note the colour changes

4. Results and Analysis

(i) Synthesis of Aspirin

Mass of salicylic acid

= 3.00 g

Mass of crystallized aspirin

= Total mass of crystallized aspirin - mass of filter paper

= 3.11g – 0.75 g

= 2.36 g

The total mass of crystallized aspirin was weighed 12.135g, but to get the mass of dry

crystallized aspirin, the aspirin was left for two days from the experiment day to air dry.

The mass of dried aspirin weighed 3.11g and the mass of filter paper is 0.75g.

Moles of salicylic acid used (mol wt of salicylic acid=138amu)

= 1mol138g

×2.36 g=0,02mol

(1 amu = 1gmol )

Theoretical number of moles of aspirin

= Moles of salicylic acid used

=0.02 mol

Theoretical grams of aspirin (mol wt of aspirin = 180 amu)

= 180gmol

×0.02mol

= 3.60 g

Percent yield

= gramsaspirin obtainedtheoretica l gramsaspirin

×100

= 2.36g3.60g

×100

= 65.56 %

When FeCl3 was added to salicylic acid, the colour changed from white to purple colour. Then it

slightly changed to brownish colour after few seconds.

When Fecl3 was added to aspirin, the colour changed from very light pink to purple colour. Then

part of it changed to brownish colour after few seconds.

When Fecl3 was added to recrystallized aspirin, the colour changed from light pink to purple.

(ii) Synthesis of Oil of Wintergreen

Methyl salicylate releases a pleasant minty odour. When FeCl3 was added to the product, a

change of colour is observed from colourless to purple colour.

5.0 Discussion

(i) Synthesis of acetylsalicylic acid

Acetylsalicylic acid is also well known as aspirin. To obtain the percentage yield, divide

mass of aspirin obtained with theoretical mass of aspirin. Theoretically, number of moles

of aspirin is equal to number of moles of salicylic acid used. It is because according to the

equation above, ratio of salicylic acid used and aspirin formed is 1:1mol in the process of

esterification.

H2SO4 acts as a catalyst in this experiment. H2SO4 will not increase the aspirin obtained

but will lower the activation energy to formed a product, so that the rate of reaction is

faster. However, to accomplish the esterification more quickly, acetic anhydride was used

instead of acetic acid in this experiment. It is because acetic anhydride is more reactive.

The suction filtration process in this experiment is to separate the residue which is

unreacted salicylic acid and acetic anhydride. The residue was washed for several times

as acetic anhydride is decomposed by the addition of water for the formation of aspirin.

To obtain the mass of aspirin without the water content, the product formed is allowed to

air dry.

Cold as opposed to warm water was used to wash the aspirin that prepared because

aspirin is more soluble in warm water. Cold water would not dissolve as much as warm

water do. As the temperature lowers, more precipitates is gained, this minimizes the

product loss. The crystal can only be caught by the filter paper, if the aspirin dissolves in

warm water, a bad yield will be gained.

Acetic acidAcetylsalicylicacid

Acetic anhydrideSalicylic acid

There is a colour change from white to purple colour when 1% of FeCl3 is added to the

salicylic acid because of the presence of phenol ring in it. When 1% of FeCl3 is added to

the aspirin obtained, the colour changed from light pink to purple because it was impure.

However, no changes of colour will occur when FeCl3 were added to pure aspirin

because the phenolic (-OH) of salicylic acid is protected by the acetate group (-OOC-

CH3).

If the experimental yield of aspirin obtained is greater than 100%, means the aspirin is

not completely dry, there is still water content in the aspirin. Thus, the mass of aspirin

recorded is higher than the mass of the theoretically aspirin.

(ii) Synthesis of Methyl salicylate

The reaction occurred between salicylic acid and methyl alcohol is also known as

esterification. The concentrated H2SO4 added in the reaction acts as a catalyst to

overcome the activation energy to form methyl salicylate.

Methyl salicylate has a common name which is Oil of Wintergreen. From the common

name, can know that methyl salicylate will release a pleasant minty odour. The minty

odour released is because esters basically will release strong and pleasant odour.

When FeCl3 is added to oil of wintergreen, the colour changed from colourless to purple

colour. It is because the phenol group in it.

6.0 Conclusion

In this experiment, both the synthesised product is formed by the common chemical

which is salicylic acid undergoes the process of esterification. Both products are an ester.

Colour changes are observed when 1% of FeCl3 is added to both products to test the

presence of phenol group. Theoretically, pure aspirin would not have any colour changes

when tested with FeCl3. However, the aspirin obtained was impure, so there was a colour

changes.

7.0 References

Acetylsalicylic Acid (Aspirin) Synthesis, online, retrieved on 9th March 2015, from

http://www.academia.edu/4728996/Acetylsalicylic_Acid_Aspirin_Synthesis

Synthesis of Aspirin and Oil of Wintergreen, online, retrieved on 9th March 2015, from

https://www.apsu.edu/sites/apsu.edu/files/chemistry/SP11_1021_Synthesis_of_Aspirin_a

nd_Oil_of_Wintergreen.pdf

Experiment 1: Preparation of aspirin and Oil of Wintergreen from Laboratory Handbook