The key difference between salicylic acid and benzoic acid is that salicylic acid has a –OH group ortho to the carboxylic acid group, whereas benzoic acid has no –OH groups in its ring structure.
Salicylic acid and benzoic acid are organic compounds. Both these compounds have a closely similar chemical structure with a slight difference. Salicylic acid has the same structure as benzoic acid but with an extra –OH group. That means; both salicylic acid and benzoic acid have a benzene ring attached to a carboxylic group, but salicylic acid has an OH group attached to the benzene ring, which is absent in benzoic acid.
CONTENTS
1. Overview and Key Difference
2. What is Salicylic Acid
3. What is Benzoic Acid
4. Side by Side Comparison – Salicylic Acid vs Benzoic Acid in Tabular Form
5. Summary
What is Salicylic Acid?
Salicylic acid is an organic compound having the chemical formula C7H6O3. It is a type of phenolic acid (an aromatic acid compound). Moreover, we can categorize this compound as a beta hydroxy acid. That means; it has a carboxylic group and a hydroxyl group separated by two carbon atoms. The molar mass is 138.12 g/mol. It appears as colourless to white crystals. Further, it is an odourless compound with a melting point 158.6 °C and a boiling point 200 °C.
Moreover, this compound has a hydroxyl group located ortho to the carboxyl group. The systematic IUPAC name of this compound is 2-hydroxybenzoic acid. Also, this compound is poorly water soluble. When considering the production, it biosynthesizes from phenylalanine (an amino acid). Moreover, we can prepare it by treating sodium phenolate with carbon dioxide at high pressure and high temperature. And, it results in producing sodium salicylate.
Figure 01: White Willow is a Natural Source of Salicylic Acid
When considering the uses of salicylic acid, it is useful as a medication to remove the outer layer of skin. It is also useful in treating warts, acne, ringworm, etc. Further, it is useful in the manufacture of different pharmaceuticals, i.e. aspirin. The other most important use is that it is a food preservative.
What is Benzoic Acid?
Benzoic acid is an organic compound having the chemical formula C7H6O2. It is a simple aromatic carboxylic acid. Also, it appears as a white crystalline solid, and it occurs naturally in many plants because it occurs as an intermediate for the biosynthesis of secondary metabolites.
Figure 02: Benzoic Acid Crystals
The name of this compound originates from its structure, which has a benzene ring with an attached carboxylic acid group. Its molar mass is 122.12 g/mol and melting point is 122 °C and 250 °C. Besides, it has a fine, pleasant odour. For industrial needs, we can produce this material via partial oxidation of toluene in the presence of oxygen.
When considering the uses of benzoic acid, it is important in the production of phenol; it is a precursor for the production of plasticizers, a precursor for the production of sodium benzoate, which is a useful food preservative, etc.
What is the Difference Between Salicylic Acid and Benzoic Acid?
Salicylic acid is an organic compound having the chemical formula C7H6O3 while benzoic acid is an organic compound having the chemical formula C7H6O2. The key difference between salicylic acid and benzoic acid is that salicylic acid has a –OH group ortho to the carboxylic acid group, whereas benzoic acid has no –OH groups in its structure.
Moreover, salicylic acid is important as a medication to remove the outer layer of skin, useful in treating warts, acne, ringworm, etc., for the production of aspirin, and as a food preservative. On the other hand, benzoic acid is important in the production of phenol; it is a precursor for the production of plasticizers, a precursor for the production of sodium benzoate which is a useful food preservative, etc. So, this is the difference between salicylic acid and benzoic acid in terms of their usage.
Below infographic provides more comparisons related to the difference between salicylic acid and benzoic acid.
Summary – Salicylic Acid vs Benzoic Acid
Salicylic acid is an organic compound having the chemical formula C7H6O3 while Benzoic acid is an organic compound having the chemical formula C7H6O2. In summary, the key difference between salicylic acid and benzoic acid is that salicylic acid has a –OH group ortho to the carboxylic acid group, whereas benzoic acid has no –OH groups in its structure.
Reference:
1. “Salicylic Acid.” Wikipedia, Wikimedia Foundation, 14 June 2019, Available here.
Image Courtesy:
1. “Thomé Salix alba clean” (Public Domain) via Commons Wikimedia
2. “Pile of benzoic acid crystals” By Devon Fyson – Own work (CC BY-SA 4.0) via Commons Wikimedia