What Is Salicylic Acid?
Salicylic acid is a compound used in topical applications for skin disorders and as an analgesic oral medication. However, if taken as is, salicylic acid may cause peritonitis due to gastrointestinal side effects. It is a beta-hydroxy acid and one of the plant hormones.
Salicylic acid is relatively easy to chemically synthesize. It is also widely found in nature, specifically in the species Cyperus rotundus and Cyperus rotundus. It is also present in the form of methyl salicylate, an ester of salicylic acid, in plant essential oils such as wintergreen oil and birch oil.
Uses of Salicylic Acid
Salicylic acid has bactericidal, anti-inflammatory, analgesic, and skin-softening properties. For this reason, it is often used in the pharmaceutical field, mainly as a topical agent for skin diseases. In addition, acetylsalicylic acid, a derivative of salicylic acid, can be widely used as an analgesic oral drug because its side effects when taken internally are reduced while maintaining the analgesic effect of salicylic acid.
Furthermore, it is also used in facial cleansers for exfoliation, as a dye intermediate, and as an antiseptic. In the past, it was also used as a preservative in foods but is currently not available as a food additive.
Properties of Salicylic Acid
Salicylic acid is a solid at room temperature and pressure, a colorless needle-like crystal with sublimation properties. Its melting point is 159°C, boiling point at 2.6 kPa is about 211°C, and its flash point and flash point are 157°C and 545°C, respectively.
It is soluble in ethanol and ether and insoluble in water. It is odorless and has a slightly sour taste.
Structure of Salicylic Acid
Salicylic acid has the structure of a benzene with one hydrogen atom replaced by a carboxy group and one hydrogen atom in the ortho position of the carboxy group replaced by a hydroxyl group.
The chemical formula is C7H6O3 with a molar mass of 138.12 g/mol. The specific formula is HOC6H4COOH, and the density is 1.443 g/cm3.
Other Information on Salicylic Acid
1. Synthesis of Salicylic Acid
Salicylic acid has a relatively simple chemical structure, so there is no need to extract it from willow, and its total synthesis is straightforward. Industrially, salicylic acid is liberated by reacting sodium phenoxide with carbon dioxide under high temperature and pressure, followed by the addition of sulfuric acid or hydrochloric acid.
The process of producing salicylic acid using this series of reactions is called the Kolbe-Schmitt reaction. In contrast, the reaction of potassium phenoxide with carbon dioxide under the same conditions can introduce a carboxy group at the para position.
Para-hydroxybenzoic acid is formed in approximately 90% of the reactions. Methyl esters to butyl esters are called parabens and are used as preservatives.
2. Reaction of Salicylic Acid
Salicylic acid, which has a phenolic hydroxyl group, reacts with ferric chloride in an aqueous solution to produce a blue to reddish-purple color. Reaction with acetic anhydride results in acetylation to form acetylsalicylic acid. Acetylsalicylic acid is one of the typical antipyretic analgesics. It is a drug synonymous with non-steroidal anti-inflammatory drugs and has anti-inflammatory, antipyretic, analgesic, and antiplatelet effects.
3. Action of Salicylic Acid
One of the actions of salicylic acid is the activation of AMP-activated protein kinase (5′ adenosine monophosphate-activated protein kinase). This is said to explain some of the effects of salicylic acid and Aspirin.
4. Metabolism of Salicylic Acid
Salicylic acid administered to humans may be excreted directly from the kidneys into the urine without being metabolized. For example, even when salicylic acid is high in human blood, such as during poisoning when a large dose of acetylsalicylic acid is taken, a large amount of salicylic acid can still be excreted in the urine.
The excretion of salicylic acid in urine increases especially when the pH of the urine is tilted toward the alkaline side. When more than 50 μg/ml of salicylic acid is present in the urine, a color reaction occurs with ferric chloride solution.