Difference Between Salicylic Acid and Glycolic Acid

Main Difference – Salicylic Acid vs Glycolic Acid

Salicylic acid and glycolic acid are organic compounds that are used in many industries as raw materials or ingredients. Salicylic acid is mainly used in medications due to its ability to remove the outer layer of skin. Glycolic acid is also used in skincare products. But these compounds have different chemical and physical properties. The main difference between salicylic acid and glycolic acid is that salicylic acid is poorly soluble in water whereas glycolic acid is highly soluble in water.

Key Areas Covered

1. What is Salicylic Acid
      – Definition, Properties, Uses
2. What is Glycolic Acid
     – Definition, Properties, Uses
3. What is the Difference Between Salicylic Acid and Glycolic Acid
    – Comparison of Key Differences

Key Terms: 2-Hydroxybenzoic Acid, Glycolic Acid, Hygroscopic, Pepto-Bismol, Salicylic Acid, Sublimation

What is Salicylic Acid

Salicylic acid is a medication that helps to remove the outer layer of the skin. It is a colorless to white crystalline solid that is odorless. The chemical formula of salicylic acid is C₇H₆O₃. The molar mass of this compound is 138.12 g/mol. The melting point of salicylic acid crystals is 158.6 °C and, it decomposes at 200 °C. These crystals can undergo sublimation at 76 °C (sublimation is the conversion of a solid directly into its vapor phase without going through a liquid phase). The IUPAC name of salicylic acid is 2-Hydroxybenzoic acid.

Figure 1: A Sample of Salicylic Acid

Salicylic acid is used as a medication. It is used to treat warts, dandruff, acne and other skin disorders due to its ability to remove the outer layer of the skin. Therefore salicylic acid is a major ingredient used in manufacturing skin care products; for example, it is used in some shampoos to treat dandruff. In addition, it is used in manufacturing Pepto-bismol, a medication used to treat gastrointestinal disorders. Salicylic acid is used as a food preservative.  

What is Glycolic Acid

Glycolic acid is the smallest alpha-hydroxy acid that has applications in many industries such as food industry, textile industry, etc. The chemical formula of glycolic acid is C₂H₄O₃. The molar mass of this compound is 76.05 g/mol. It is available as a white powder. The melting point of glycolic acid is 75 °C and it decomposes at high temperatures.

Figure 2: Chemical Structure of Glycolic Acid

Glycolic acid is highly soluble in water. It is also hygroscopic (it can absorb water vapor when exposed to air). This compound has various applications. In the textile industry, glycolic acid is used as a dyeing agent and as a tanning agent. In the food industry, it is used as a food additive and flavoring agent. In the pharmaceutical industry, it is used as a skin care agent. It is also used in manufacturing adhesives and plastics.

Difference Between Salicylic Acid and Glycolic Acid

Definition

Salicylic Acid: Salicylic acid is a medication that helps to remove the outer layer of the skin.

Glycolic Acid: Glycolic acid is the smallest alpha-hydroxy acid, which has applications in many industries.

Chemical Formula

Salicylic Acid: The chemical formula of salicylic acid is C₇H₆O₃.

Glycolic Acid: The chemical formula of glycolic acid is C₂H₄O₃.

Molar Mass

Salicylic Acid:  The molar mass of salicylic acid is 138.12 g/mol.

Glycolic Acid:  The molar mass of glycolic acid is 76.05 g/mol.

Melting Point

Salicylic Acid: The melting point of salicylic acid crystals is 158.6 °C.

Glycolic Acid: The melting point of glycolic acid is 75 °C.

Appearance

Salicylic Acid:  Salicylic acid is a colorless to white crystalline solid that is odorless.

Glycolic Acid: Glycolic acid is available as a white powder.

Solubility in Water

Salicylic Acid:  Salicylic acid is poorly soluble in water.

Glycolic Acid: Glycolic acid is highly soluble in water.

Hygroscopy

Salicylic Acid:  Salicylic acid is not a hygroscopic compound.

Glycolic Acid:  Glycolic acid is hygroscopic.

Uses

Salicylic Acid:  Salicylic acid is used to treat warts, dandruff, acne and other skin disorders, used in manufacturing Pepto-bismol and used as a food preservative

Glycolic Acid: Glycolic acid is used as a dyeing agent and as a tanning agent, as a food additive and flavoring agent and as a skin care agent.

Conclusion

Salicylic acid and glycolic acid are important compounds used in pharmaceutical industry for the manufacturing of different skin care products. The main difference between salicylic acid and glycolic acid is that salicylic acid is poorly soluble in water whereas glycolic acid is highly soluble in water.

Reference:

1. “Salicylic acid.” Wikipedia, Wikimedia Foundation, 29 Jan. 2018, Available here.
2. “Glycolic acid.” Wikipedia, Wikimedia Foundation, 29 Jan. 2018, Available here.

Image Courtesy:

1. “Salicylic acid sample” By Adam Rędzikowski – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Glycolic acid” By STALLKERL – Selbstgezeichnet mit ChemSketch (Public Domain) via Commons Wikimedia