SALICYLIC ACID
Salicylic acid is an important pharmaceutical compound widely used in skin-care and dermatology. It works mainly as a keratolytic agent, meaning it helps remove the upper dead layer of skin. Below is a simple and clear explanation useful for Pharm.D and pharmacy students.
1. Chemical Formula
C7H6O3
2. Preparation (Kolbe’s Reaction)
Salicylic acid is prepared by:
- Treating sodium phenoxide with carbon dioxide (CO₂)
- The reaction takes place at about 125°C under 6 atmospheres pressure
- The product is then acidified to obtain salicylic acid
This method is called the Kolbe Reaction.
3. Tests for Purity
Pharmaceutical-grade salicylic acid must meet specific purity limits:
- Appearance: 10% solution in ethanol should be clear
- Heavy metals: less than 100 ppm
- Iron: less than 2 ppm
- Chlorides: less than 125 ppm
- Sulfates: less than 200 ppm
- Sulfated ash: less than 2 g
- Loss on drying: less than 0.5%
4. Assay
Salicylic acid is assayed by acid-base titration using 0.1 M NaOH. Ethanol is added to improve solubility.
Conversion factor: 1 ml of 0.1 M NaOH = 0.01381 g of salicylic acid
Alternative method:
Titration with N/2 NaOH in alcohol using phenol red indicator until the sodium salt is completely formed.
Because of the –OH group (ortho position), salicylic acid is stronger than benzoic acid.
5. Uses
Salicylic acid is used in many pharmaceutical and cosmetic preparations:
- As an antiseptic and disinfectant
- As a keratolytic agent (helps remove dead skin)
- Treatment of acne, dandruff, seborrhea, psoriasis
- Used to remove warts, corns, and calluses
Detailed Notes:
For PDF style full-color notes, open the complete study material below:
PATH: PHARMD/PHARMD NOTES/ PHARMD FIRST YEAR NOTES/ ORGANIC CHEMISTRY/ PHARMACEUTICAL ORGANIC CHEMISTRY/ SALICYLIC ACID.