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Preparation of aspirin from methyl salicylate
Aspirin can be prepared from methyl salicylate by a two-step synthesis as follows:
Step 1: Hydrolysis of methyl salicylate to form salicylic acid
In this step, methyl salicylate is hydrolyzed in the presence of NaOH to give a corresponding sodium salt, which, on acidification, gives salicylic acid.
Step 2: Esterification of salicylic acid
Salicylic acid is esterified with acetic acid to obtain aspirin.
Procedure
- Mix 100 mL of distilled water, 4 mL of methyl salicylate, and 10 g of NaOH and reflux in a water bath for 30 minutes.
- Cool the hot solution until the temperature falls to room temperature.
- After cooling, acidify this solution with conc. HCl. A white precipitate of salicylic acid will be formed. Filter, recrystallize, and dry.
- Measure the weight of the dry white precipitate. ( We measured 3.512 g in total.)
- Mix 3.512 g of salicylic acid with 3 mL of acetic acid and a few drops of H2SO4.
- Heat the mixture for 10 minutes and add 20 mL of water.
- Allow the mixture to cool in the ice bath. Recrystallize it either with water or ethanol.
- Filter, dry, and weigh the obtained precipitate upon recrystallization.
Observation
Volume of methyl salicylate taken: 4 mL
Specific gravity of methyl salicylate: 1.176
Weight of methyl salicylate taken: 4×1.176 =4.704 g
Amount of salicylic acid obtained: 3.512 g https://www.roundtowers.org.uk/
Amount of aspirin obtained: 3.21 g
Calculation
For salicylic acid:
152.14 g of methyl salicylate forms 138.121 g of salicylic acid.
4.704 g of methyl salicylate mulia288 forms Y g salicylic acid.
Y=(138.121/152.14)× 4.704 = 4.27 g
Hence, theoretical yield: 4.27 g
Here, actual yield of salicylic acid: 3.512 g
Now, % yield= (Actual yield/Theoretical yield)× 100 % = (3.512/4.27) × 100 % = 82.24 %
For aspirin:
138.12 g of salicylic acid forms 180.158 g of aspirin.
3.512 g of salicylic acid forms Y g aspirin.
Y = (180.158/138.12)× 3.512 = 4.58 g
Hence, theoretical yield: 4.58 g
Here, actual yield of aspirin: 3.21 g
Now, % yield= (Actual yield/Theoretical yield) × 100 % = (3.21/4.58) × 100 % = 70.08 %
Melting point of salicylic acid and aspirin
The melting points of salicylic acid and aspirin can be determined by using Thiele’s tube. The reported melting points and observed melting points are listed in the table:
| Compounds | Reported melting points | Observed melting points |
| Salicylic acid | 158 °C | 150 °C |
| Aspirin | 135 °C | 128 °C |
IR spectrum of salicylic acid
Four major peaks are found in the FTIR spectrum of salicylic acid. Since, there is the presence of -OH group, a broad peak of -COOH is observed around 2500–3500 cm-1 . A small, sharp peak is obtained around 3200 cm-1 which is due to -OH group. Due to carbonyl stretching (C=O), there is a peak at about 1660 cm-1. Due to the C-O bond, there is a peak at about 1296 cm-1 wave number.
IR spectrum of aspirin
Due to the presence of hydroxyl group (-OH), there is a peak at about 3200 cm-1 wave number in IR spectrum. A peak at around 1680 cm-1 wave number is seen due to the carbonyl stretching. Since, there is also a presence of C-O bond, a peak at around 1296 cm-1 wave number is seen.
RESULT
Aspirin was prepared from methyl salicylate by two-step synthesis through salicylic acid. The yield percentage of salicylic acid and aspirin https://www.mediterraneanknowledge.org/publications/ was found to be 82.24% and 70.08%, respectively. The melting points of salicylic acid and aspirin were also found to be 150 and 128 °C, respectively. Similarly, from the IR spectra of the compound, the functional groups of salicylic acid were found to be -OH, -COOH, and that of aspirin was -COOH and -O-C=O. https://sgipi.utch.edu.co/gestion-investigativa/
CONCLUSION
Hence, aspirin can be prepared by two-step synthesis starting from methyl salicylate and the functional group of starting and synthesized product can be identified by IR spectroscopy