This document describes the preparation of aspirin from salicylic acid. Aspirin is synthesized through an esterification reaction, where salicylic acid reacts with acetic anhydride in the presence of sulfuric acid as a catalyst. This replaces the phenolic hydroxyl group of salicylic acid with an acetyl group, forming aspirin and acetic acid as a byproduct. Specifically, 10g of salicylic acid is reacted with 14mL of acetic anhydride and 2mL of sulfuric acid by heating on a water bath for 30 minutes. The crude aspirin product is then purified by recrystallization in ethanol. The percentage yield of aspirin is then calculated based on the theoretical

1. Preparation of Aspirin from Salicylic acid
Mrs Chanda Ranjan
Department of Pharmaceutical Chemistry
The Oxford College of Pharmacy, Bangalore

2. Learning outcome
1. How Aspirin is synthesized in the laboratory?
2. Calculation of the practical yield.

3. Content:
• Materials Required.
• Principle
• Procedure
• Calculation
• Report.

4. 1. Chemically Aspirin is 2-Acetoxybenzoic acid.
2. Aspirin is an effective analgesic (pain reliever), antipyretic (fever reducer) and
anti-inflammatory agent and is one of the most widely used non-prescription drugs.
1. Salicylic acid contains a phenol group, and phenols are known to be irritating.
2. Due to this the phenol group was replaced with acetyl group that become
(acetylsalicylic acid, also known as aspirin) which was shown to be much less
irritating than salicylic acid.
Preparation of Aspirin from Salicylic acid
Chemicals Required: Salicylic acid, acetic anhydride, conc Sulphuric acid, Ethanol.
Apparatus Required: Beaker, Funnel, Stirrer, Pipette
Materials Required

5. 1. Aspirin can be made by reacting salicylic acid with Acetic anhydride in the presence of an acid
catalyst. This reaction is an example of Esterification reaction.
2. The OH group (phenol group) on the salicylic acid forms an acetylated product with the acetic
anhydride.
3. Salicylic reacts with acetic anhydride and with the aid of acidic condition the acetate ion detaches
from the acetic anhydride and gets attached to the hydrogen ion released from the phenolic OH
group and forms Acetic acid as the byproduct.
5. And the hydrogen ion of phenolic OH is replaced with Acetyl group resulting the formation of Aspirin
Preparation of Aspirin from Salicylic acid
Principle
4. The Acetic acid formed as the byproduct is washed with water and the remaining acetic anhydride
also reacts with water to form acetic acid and then washed with water

6. Procedure
1. 10 gm of salicylic acid, 14 ml of acetic anhydride, and 2 ml of concentrated sulphuric acid was taken
in a beaker and heated over the water bath for half an hour at 60 to 65 degree C with continuous stirring
10 gm Salicylic acid
14 ml acetic anhydride
2ml conc Sulphuric acid
Cold Water
2. After heating the mixture was poured into the cold water with occasional stirring.
Preparation of Aspirin from Salicylic acid
Water bath

7. 3. After some time the crude Aspirin was filtered.
Crude aspirin
30 ml Ethanol + Crude Aspirin
Warm
water
4. The product will be dissolved in alcohol for recrystallization
5. After that it will be poured into warm water so that the solid separates
Preparation of Aspirin from Salicylic acid
Procedure

8. Cold Water
Aspirin
6. The separated solid will be filtered and dried and after that its weight and melting point
determination will be done.
Preparation of Aspirin from Salicylic acid
White,
Crystalline Solid
melting point - 136 °C
boiling point - 140 °C .

9. Calculation
• Molecular weight of Salicylic acid = 138 gm
• Molecular weight of Aspirin= 180 gm
• 138 gm of salicylic acid gives  180 gm of Aspirin
• Therefore, 10 gm of salicylic acid will give  180 x 10 = 13.04 gm of Aspirin
________
138
• Theoretical yield = 13.04 gm
• Practical yield= ________ gm
• Percentage yield= Practical Yield x 100
___________________
Theoretical yield
Preparation of Aspirin from Salicylic acid

10. Thank You