Methyl Salicylate
Formula
C8H8O3
IUPAC Name
Methyl 2-hydroxybenzoate
Introduction
Methyl salicylate is an ester made from salicylic acid. It has a strong, pleasant smell and is commonly used in pain-relief ointments, balms, and liniments. It is also known as wintergreen oil.
Preparation
Methyl salicylate is prepared by reacting salicylic acid with methanol in the presence of concentrated sulphuric acid (H2SO4). This process is called esterification.
Tests for Purity
- Appearance: 2 ml mixed with 10 ml ethanol should give a clear solution.
- Acidity: Should require less than 0.4 ml of 0.1 M NaOH.
- Refractive Index: Should be between 1.534 and 1.538.
- Density: Should be between 1.175 and 1.185 g/ml.
Assay
The assay is done by saponification (alkaline hydrolysis). Alcoholic KOH is added, which breaks the ester. The remaining alkali is then measured to determine how much was consumed.
Another method involves hydrolysing the ester using strong alkali and back-titrating the unused NaOH with HCl.
Conversion Factor: 1 ml of 0.1 M NaOH ≡ 0.01522 g of sodium salicylate.
Uses
- Used in hair tonics and ointments for pain relief.
- Common ingredient in creams for aches, sprains, muscle pain, and bruises.
- Acts as a topical analgesic (pain-relieving agent).
Detailed Notes:
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