This document describes the synthesis of aspirin from salicylic acid and acetic anhydride. Sulfuric acid is used to catalyze the reaction by protonating acetic anhydride. This allows the acyl group to be transferred from acetic anhydride to salicylic acid, forming aspirin. The reaction mechanism and protocol for synthesizing aspirin in the lab are provided. Infrared spectroscopy is used to analyze the product and confirm aspirin formation by identifying characteristic carbonyl peaks that are present in aspirin but absent in salicylic acid.

1. Synthesis of Aspirin from salicylic acid
Abstract
The main objective of this experiment is synthesis mechanism of aspirin in mole from
salicylic acid and acetic anhydride in the presence of sulfuric acid. Acetic anhydride is used
as an acylating agent which is accelerated by sulfuric acid. Sulfuric acid will protonate
oxygen of acetic anhydride in first step. Then hydroxyl group of salicylic acid will react with
protonated acetic anhydride. Third is deprotonation step which is occur by sulfate ion. Lone
pair of oxygen resonate and convert it into acetylsalicylic acid by removing acetate ion.
Reaction
Salicylic acid Acetic anhydride
Aspirin
(Acetylated alicylic acid)
H2
SO4 H
2
SO
4
Fig 1. Overall reaction for Aspirin synthesis
Mechanism
..
..
HSO
4
-
..
Aspirin
Fig 2. Mechanism for Aspirin synthesis

2. Protocol
1. Weight out 2.027g of salicylic acid using electrical balance.
2. Take 5 mL acetic anhydride as by using a measuring cylinder
3. Transfer salicylic acid into Erlenmeyer, added in this 5ml acetic anhydride, mixes it
well.
4. Add in this 5drops of concentrated sulfuric acid, which making an acidic environment
and will also cause a reaction to go a little faster.
5. Heat the mixture in a water bath for about 10 minutes, after 10 minutes reaction
mixture colour becomes to yellowish brown tint.
6. Then add to this reaction 10 mL cold water and put the reaction conical flask in a cold
water bath.
7. Allow the aspirin crystals to form, after 10 minutes later you see a lot of aspirin
crystallized in our Erlenmeyer.
8. Filter out the aspirin from the solution by using a sidearm flask and a suction filter.
9. Collect the filtered product (Aspirin) in beaker, added to this Ethanol
10. Recrystallize the aspirin, by dissolve aspirin in ethanol, to get larger crystals of the
acetylsalicylic acid.
11. Added 60mL of warm water, it becomes cloudy actually a little bit of crystallization is
occurring here, stir well.
12. Allow to stand it in ice water bath, wait for the crystal to form.
13. Take a filter paper, weigh it is 0.354g and set up it in filtering apparatus again and
filter the mixture.
14. Take out our filter paper with the aspirin on it, set it on a watch glass and allow to air
dry.
15. Weigh our dried filter paper and aspirin that is 2.711g collect the aspirin crystal and
weigh of pure aspirin is 2.35g.
Results
A) Purification step for aspirin
Collect the filtered product (Aspirin) in beaker, added to this Ethanol .Recrystallize the
aspirin, by dissolve aspirin in ethanol, to get larger crystals of the acetylsalicylic acid. Added
60mL of warm water, it becomes cloudy actually a little bit of crystallization is occurring
here, stir well. Allow to stand it in ice water bath, wait for the crystal to form. Take a filter
paper, weigh it is 0.354g and set up it in filtering apparatus again and filter the mixture. Take
out our filter paper with the aspirin on it, set it on a watch glass and allow to air dry. Weigh
our dried filter paper and aspirin that is 2.711g collect the aspirin crystal and weigh of pure
aspirin is 2.35g.
B) By comparing the infrared spectrum of aspirin and salicylic acid identifying the product
Started with aspirin IR spectrum (fig.1) we can identify an -OH bond in carboxylic acid
which corresponding to this OH bond peak at 3000cm-1
to 3200cm-1
and two peaks at
1700cm-1
to 1800cm-1
correspond to the C=O bond in like acid and esters so that’s one C=O
bond in the carboxylic group and one C=O in the ester group.

3. Fig.3 IR spectrum of Aspirin
Look at the IR spectrum of salicylic acid. In this spectrum there are 2 differences to the
spectrum of aspirin, in the first difference is the peak that appear at 3600cm-1
corresponds to
the -OH bond in phenols which is absent in IR spectrum of aspirin. The second difference is
the absence of 2 peak at1700cm-1
to 1800cm-1
that corresponds to C=O carbon to oxygen
double bond in ester instead there’s only one peak that corresponds to carbon-to-oxygen
double bond in carboxylic acid
Fig.4 IR spectrum of salicylic acid
Reference
1. Barry, E., & Borer, L. L. (2000). Experiments with aspirin. Journal of Chemical
Education, 77(3), 354.
2. El-Magbri, M. (2014). The Synthesis and Analysis of Aspirin. Washington, DC,
20016.
3. Maradiaga, E. Aspirin lab report TA: Dr. Dehghan 3/17/2016.
4. Olmsted III, J. A. (1998). "Synthesis of aspirin: A general chemistry experiment."
Journal of Chemical Education 75(10): 1261.