Salicylic Acid vs Glycolic Acid
Carboxylic acids are the organic compounds having the functional group –COOH. This group is known as the carboxyl group. Carboxylic acid has a general formula as follows.
In the simplest type of carboxylic acid, R group equals to H. This carboxylic acid is known as formic acid. Further, R group can be a straight carbon chain, branched chain, aromatic group etc. Salicylic acid and glycolic acid are two such carboxylic acids with different R groups.
In the IUPAC nomenclature, carboxylic acids are named by dropping the final –e of the name of the alkane corresponding to the longest chain in the acid and by adding –oic acid. Always, the carboxyl carbon is assigned number 1. Carboxylic acids are polar molecules. Because of the –OH group, they can form strong hydrogen bonds with each other and with water. As a result, carboxylic acids have high boiling points. Further, carboxylic acids with lower molecular weights easily dissolve in water. However, as the length of the carbon chain increases, the solubility decreases.
Salicylic acid is the common name used to address monohydroxybenzoic acid. It is an aromatic compound where a carboxylic group is attached to a phenol. Rhw OH group is at the ortho position to the carboxyl group. In IUPAC nomenclature, it is named as 2-hydroxybenzenecarboxylic acid. It has the following structure.
Salicylic acid is a crystalline solid, and it is colorless. This substance was earlier isolated from the bark of the willow tree; thus, it got the name from the Latin word Salix, which is used to indicate willow tree. Molar mass of salicylic acid is 138.12 g mol-1. Its melting point is 432 K, and its boiling point is 484 K. Salicylic acid is soluble in water. Aspirin has a similar structure as to salicylic acid. Aspirin can be synthesized from the esterification of the phenolic hydroxyl group of salicylic acid with the acetyl group from acetyl chloride.
Salicylic acid is a plant hormone. It has a plant growth and development role in plants. Further it assists with photosynthesis, transpiration, ion uptake and transport in plants. In nature, it is synthesized within plants from the amino acid phenylalanine. Salicylic acid is used for medicinal and cosmetic uses. Especially it is used to treat acne prone skins to reduce pimples and acne. It is an ingredient in shampoos, to treat dandruff. It is used as a medicine, to reduce fevers and ease aches and pains. It is also an essential micronutrient needed for human. Fruits and vegetables like dates, raisins, blueberries, guavas, tomatoes, and mushrooms contain salicylic acid. Not only salicylic acid, but its derivatives are also useful in different means.
Glycolic acid is also known as hydroxyacetic acid or 2-hydroxyethanoic acid. It is a crystalline solid with no color, no odor. Glycolic acid is hygroscopic and highly soluble in water. It has the following structure. It is the smallest alpha-hydroxy acid.
Molar mass of glycolic acid is 76.05 g/mol. The melting point is 75 °C. It is naturally present in fruits and also in sugar cane.
Glycolic acid is mainly used in skin care products. It has the ability to penetrate the skin which makes it suitable for skin care products.
What is the difference between Salicylic Acid and Glycolic Acid?
• Salicylic acid is a beta-hydroxy acid whereas glycolic acid is an alpha-hydroxy acid.
• Glycolic acid is much smaller compared to salicylic acid.
• Salicylic acid is more soluble in oil, whereas glycolic acid is more soluble in water.
• Salicylic acid is a better ingredient in acne treatment products than glycolic acid.