Salicylic acid
[CAS# 69-72-7]

Identification

• Classification: API >> Synthetic anti-infective drugs >> Disinfectant antiseptic
• Name: Salicylic acid
• Synonyms: 2-Hydroxybenzoic acid
• Molecular Formula: C₇H₆O₃
• Molecular Weight: 138.12
• CAS Registry Number: 69-72-7
• EC Number: 200-712-3
• SMILES: C1=CC=C(C(=C1)C(=O)O)O

Properties

• Solubility: 1.8 g/L (water, 20 °C), 1 M (ethanol, 20 °C)
• Density: 1.4±0.1 g/cm³, Calc.^*, 1.443 g/mL
• Index of Refraction: 1.616, Calc.^*, 1.565
• Melting point: 158-161 °C
• Sublimation: 70 °C
• Boiling Point: 336.3±0.0 °C (760 mmHg), Calc.^*, 211 °C
• Flash Point: 144.5±19.1 °C, Calc.^*, 157 °C

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software.

Safety Data

• Hazard Symbols: GHS08;GHS07;GHS05 Danger
• Risk Statements: H302-H312-H318-H319
• Safety Statements: P264-P264+P265-P270-P280-P301+P317-P302+P352-P305+P351+P338-P305+P354+P338-P317-P321-P330-P337+P317-P362+P364-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Acute toxicity	Acute Tox.	4	H302
Eye irritation	Eye Irrit.	2	H319
Serious eye damage	Eye Dam.	1	H318
Acute toxicity	Acute Tox.	4	H312
Reproductive toxicity	Repr.	2	H361
Skin irritation	Skin Irrit.	2	H315
Specific target organ toxicity - single exposure	STOT SE	3	H335
Reproductive toxicity	Repr.	2	H361d
Acute toxicity	Acute Tox.	4	H332
Acute toxicity	Acute Tox.	2	H330
Chronic hazardous to the aquatic environment	Aquatic Chronic	3	H412
Specific target organ toxicity - repeated exposure	STOT RE	1	H372
Specific target organ toxicity - single exposure	STOT SE	2	H371
Reproductive toxicity	Repr.	2	H361d

Discovery and Applications

Salicylic acid, with the chemical formula C7H6O3, is a colorless, crystalline organic acid. It is a naturally occurring compound found in various plants, particularly in the bark of willow trees (Salix spp.), from which its name is derived. The discovery of salicylic acid dates back to ancient times when willow bark was used for its medicinal properties. However, it was not until the 19th century that salicylic acid was isolated and studied in detail.

In 1838, the German chemist Johann Franz Adam Schmidt first isolated salicin, a glycoside found in willow bark. Salicin was later hydrolyzed to produce salicylic alcohol, and in 1860, the French chemist Henri Leroux successfully synthesized salicylic acid from sodium salicylate through the hydrolysis of salicin. This work marked a significant advancement in understanding salicylic acid's structure and properties, laying the foundation for its subsequent applications in medicine and chemistry.

Salicylic acid has since gained recognition for its wide range of applications, particularly in the pharmaceutical and cosmetic industries. One of its most well-known uses is as a key ingredient in the formulation of aspirin (acetylsalicylic acid). Aspirin was first synthesized in 1897 by Felix Hoffmann at Bayer, who acetylated salicylic acid to reduce its gastrointestinal side effects while preserving its analgesic and anti-inflammatory properties. Today, aspirin remains one of the most widely used medications globally, primarily for pain relief, anti-inflammatory purposes, and cardiovascular health.

In addition to its role in aspirin production, salicylic acid is utilized in various dermatological products due to its keratolytic properties. It is effective in treating skin conditions such as acne, psoriasis, and dandruff. Salicylic acid works by promoting the shedding of dead skin cells and reducing inflammation, making it a popular active ingredient in topical treatments. Formulations containing salicylic acid are commonly found in over-the-counter acne treatments, medicated shampoos, and exfoliating products.

Moreover, salicylic acid serves as a crucial compound in the synthesis of various chemicals and materials. It is used as a precursor for the production of synthetic dyes, fragrances, and other organic compounds. In the field of agriculture, salicylic acid plays a role in plant growth regulation and stress response. It is known to enhance the plant's defense mechanisms against pathogens and environmental stresses, making it valuable for improving crop resilience and yield.

Salicylic acid also has applications in analytical chemistry. It is commonly employed as a reagent in various analytical techniques, including spectrophotometry and chromatography. Its ability to form complexes with metal ions enables its use in determining the concentration of certain metals in samples, contributing to environmental monitoring and quality control.

Despite its numerous beneficial applications, safety considerations are essential when handling salicylic acid. It can cause skin and eye irritation upon contact, and prolonged exposure may lead to more severe effects. Therefore, proper handling and safety precautions should be observed when working with this compound.

In conclusion, salicylic acid is a versatile organic compound with a rich history of discovery and a broad spectrum of applications in medicine, cosmetics, agriculture, and analytical chemistry. Its significance in both historical and contemporary contexts highlights its enduring value in various fields.

References

2016. Verruca Vulgaris. Dermatopathology.
DOI: 10.1007/978-3-319-30006-1_480

1984. Increased Skin Permeability for Lipophilic Molecules. Journal of Pharmaceutical Sciences, 73(8).
DOI: 10.1002/jps.2600730831

2024. Unraveling the phytochemical complexity and antimicrobial potency of introduced versus native Argania spinosa trees in Eastern Morocco. Chemical Papers, 78(12).
DOI: 10.1007/s11696-024-03739-1