Salicylic Acid

Salicylic acid: Salicylic acid is a well-known chemical compound widely used in skincare and medicine. As a beta-hydroxy acid (BHA), it is famous for its ability to treat various skin conditions, such as acne, dandruff, and psoriasis. Its chemical properties make it an effective keratolytic agent, which helps remove dead skin cells and promote healthy skin renewal.

This colorless crystalline organic acid is found naturally in plants and can also be synthesized through chemical processes. Salicylic acid is a key ingredient in many over-the-counter skincare products, particularly anti-acne treatments, due to its ability to penetrate the skin, unclog pores, and reduce inflammation.

Apart from its skin benefits, salicylic acid is used in the production of important medications like aspirin, which is commonly used for pain relief and as a blood thinner. It also has antifungal and bacteriostatic properties, making it a vital component in treatments for various skin infections.

Whether used topically in lotions or incorporated into more complex treatments, salicylic acid plays an essential role in both skincare routines and pharmaceutical products. In this article, we will explore its chemical structure, physical and chemical properties, uses, and the best methods for preparing this versatile compound.

By understanding the science behind salicylic acid, you can appreciate its value in healthcare, skincare, and medicinal applications. Keep reading to learn more about its benefits, uses, and safety precautions when applying salicylic acid to your daily regimen.

What is Salicylic Acid?

Salicylic acid is a beta-hydroxy acid (BHA) and a kind of phenolic acid. Plants are a natural source of beta hydroxy acid. Organic synthesis makes extensive use of this colorless crystalline organic acid. It comes from the way salicin is metabolized. A crystalline organic carboxylic acid, salicylic acid possesses fungicidal, bacteriostatic, and keratolytic qualities.

It is toxic to human bodies when ingested in large quantities. When used in modest amounts, it is primarily used as an antiseptic and in topical treatments for skin conditions like acne. A carboxyl group, or COOH, is affixed to salicylic acid. It has no color and no smell.

It is most likely well-known for being a key component of topical anti-acne medications. Salicylates are salicylic acid's salts and esters.

Structure of Salicylic Acid

Salicylic acid's structural formula is C₆H₄(OH)COOH. In the condensed form, the chemical formula can also be expressed as C₇H₆O₃. Salicylic acid is known by its IUPAC name, 2- hydroxybenzoic acid. A hydroxyl group, or -OH group, is linked to salicylic acid at the ortho position in relation to the carboxylic acid. The benzene ring contains this COOH group.

Salicylic acid's molar mass, or molecular weight, is 138.12 g/mol.

Every carbon atom in salicylic acid's benzene ring undergoes sp² hybridization. Salicylic Acid creates a hydrogen bond inside molecules. Salicylic acid dissociates from the carboxylic acid in an aqueous solution in order to lose a proton. The hydrogen atom of the hydroxyl group, or - OH, interacts with the resultant carboxylate ion, or −COO−, by intermolecular contact. As a result, an intramolecular hydrogen bond is formed.

Methods of Preparing Salicylic Acid

The two most commonly used methods for preparing salicylic acid are as follows:

• From phenol: When phenol reacts with sodium hydroxide, it produces sodium phenoxide. Sodium phenoxide is then distilled and dehydrated. This process is followed by a carboxylation reaction with carbon dioxide, which produces sodium salicylate, a salt of salicylic acid. This salt was then reacted with an acid, hydronium ion, or any species that represents a proton to produce salicylic acid.
• From Methyl Salicylate: Methyl salicylate, often known as wintergreen oil, is extensively used as an analgesic in the pharmaceutical sector. It is used to prepare salicylic acid. In this reaction, methyl salicylate reacts with sodium hydroxide (NaOH), resulting in the creation of a sodium salt intermediate of salicylic acid. This acid is known as disodium salicylate, and it reacts with sulfuric acid to produce salicylic acid.

Physical Properties of Salicylic Acid

• At room temperature, salicylic acid forms colorless, odorless needle-shaped crystals. Salicylic acid has an unpleasant taste.
• Its boiling and melting points are 211 and 315 degrees Celsius, respectively.
• Salicylic acid contains two hydrogen bond donors and three acceptors.
• Salicylic acid has a flashpoint of 157°C.
• At 25°C, its lipophilic nature results in a low water solubility of only 1.8 g/L.
• Salicylic acid is soluble in organic solvents such as carbon tetrachloride, benzene, propanol, ethanol, and acetone. Its density is 1.44 at 20°C.
• The vapor pressure is 8.2×105mmHg at 25°C.
• It has a tendency to discolor when exposed to direct sunshine due to photochemical deterioration.
• When degraded, it produces noxious odors and acrid smoke.
• At 25°C, its heat of combustion is 3.026mj/mole.
• A saturated solution of salicylic acid has a pH of 2.4. The pka value (dissociation constant) is 2.97.

Chemical Properties of Salicylic Acid

• Aspirin is created by the following steps: In the pharmaceutical business, the most important reaction related with salicylic acid utilization is the synthesis of aspirin, also known as acetylsalicylic acid.
• It is one of the most widely used analgesics and blood thinners. In this reaction, salicylic acid reacts with acetic anhydride. It causes the acetylation of the hydroxyl group in salicylic acid, which results in the synthesis of acetylsalicylic acid, or aspirin. Acetic acid is produced as a byproduct of this process. This is also present as an impurity in the large-scale manufacture of aspirin.
• Esterification Reaction: Because salicylic acid is an organic acid, it reacts with organic alcohol groups to form a new organic chemical class-like ester. When salicylic acid reacts with methanol in an acidic media, preferably sulphuric acid, in the presence of heat, a dehydration reaction occurs, resulting in the loss of water - OH− ions. This ion is lost from the carboxylic acid functional group of the salicylic acid molecule, whereas the H+ ion is lost during the deprotonation of the methanol molecule, resulting in the creation of methyl salicylate (an ester).

Uses of Salicylic Acid

• Salicylic acid is widely used in the pharmaceutical business.
• The most prevalent application of salicylic acid is in the manufacture of aspirin, an acetylated derivative of salicylic acid.
• Another analgesic derived from salicylic acid is methyl salicylate, an esterified derivative of salicylic acid. Both of these analgesics are used to treat headaches and other physical pains.
• Salicylic acid is used to treat wart infections. Professionals cure warts via a process comparable to its keratolytic activity. First, it dehydrates the wart-affected skin cells, causing them to eventually shed from the body.
• It also activates the body's immune response to the viral wart infection, causing a minor inflammatory reaction.
• Salicylic acid is a key component of anti-dandruff shampoos. This acid also helps to remove dry and flaky skin cells from your scalp.
• Salicylic acid is also used as a mild antiseptic, known as a bacteriostatic agent. It does not destroy existing bacteria and hence is not an antibacterial agent, but rather prevents bacteria from growing wherever it is applied.

Conclusion

Salicylic acid is a beta-hydroxy acid (BHA) and a type of phenolic acid found in plants. It is a colorless crystalline organic acid with fungicidal, bacteriostatic, and keratolytic properties. It is toxic to humans when consumed in large quantities but can be used in modest amounts as a food preservative and antiseptic. Salicylates are salts and esters of salicylic acid, and it is listed on the World Health Organization's List of Essential Medicines.

Salicylic acid is produced by phenol reacting with sodium hydroxide, resulting in sodium salicylate. It is soluble in organic solvents and has a flashpoint of 157°C. It is also used in the pharmaceutical industry for the manufacture of aspirin, methyl salicylate, wart infections, anti-dandruff shampoos, and as a mild antiseptic. Its chemical properties include being a source of aspirin, an acetylated derivative, and an esterified derivative, methyl salicylate. Salicylic acid is a safe and efficient medication required in healthcare systems.