Thiosalicylic acid
[CAS# 147-93-3]

Identification

• Classification: Chemical reagent >> Organic reagent >> Thiol/thiophenol
• Name: Thiosalicylic acid
• Synonyms: 2-Mercaptobenzoic acid
• Molecular Formula: C₇H₆O₂S
• Molecular Weight: 154.18
• CAS Registry Number: 147-93-3
• EC Number: 205-704-3
• SMILES: C1=CC=C(C(=C1)C(=O)O)S

Properties

• Density: 1.49 g/mL
• Melting point: 164-169 °C
• Flash point: 150 °C
• Water solubility: soluble in hot water

Safety Data

• Hazard Symbols: GHS07 Warning
• Risk Statements: H315-H319-H335
• Safety Statements: P261-P264-P264+P265-P271-P280-P302+P352-P304+P340-P305+P351+P338-P319-P321-P332+P317-P337+P317-P362+P364-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Skin irritation	Skin Irrit.	2	H315
Eye irritation	Eye Irrit.	2	H319
Specific target organ toxicity - single exposure	STOT SE	3	H335
Acute toxicity	Acute Tox.	4	H332
Acute toxicity	Acute Tox.	4	H312
Acute toxicity	Acute Tox.	4	H302

Discovery and Applications

Thiosalicylic acid was originally synthesized by reacting salicylic acid with hydrogen sulfide (H2S) or thionyl chloride (SOCl2) under controlled conditions. This synthetic route introduces a thiol group (-SH) into the aromatic ring, converting salicylic acid into its thiol derivative. The unique chemical properties of this compound pave the way for its application in various fields.

Thiosalicylic acid is characterized by the substitution of the benzene ring with a carboxylic acid group (-COOH) and a thiol group (-SH) in the ortho position. This structure makes it acidic and thiol, affecting its solubility and reactivity in chemical reactions. Thiosalicylic acid is usually present in the form of white to pale yellow crystalline powder or flakes. It is slightly soluble in water, but readily soluble in polar organic solvents such as ethanol, methanol, and acetone. Thiosalicylic acid behaves as a weak acid in aqueous solution, releasing hydrogen ions (H⁺) upon ionization. The presence of the thiol group (-SH) imparts additional nucleophilic and chelating properties. Since the sulfur atom is able to coordinate with metal centers, thiosalicylic acid forms complexes with various metal ions, especially heavy metals such as mercury (Hg) and silver (Ag).

Thiosalicylic acid is used as a chelating agent in analytical chemistry for the determination and quantification of metal ions in solution. The ability of thiosalicylic acid to form stable complexes with metals is used in spectrophotometry and titration to improve the sensitivity and selectivity of metal analysis.

Research has explored the antioxidant properties of thiosalicylic acid and its derivatives, which have shown efficacy in combating oxidative stress-related diseases. The chelating ability of this compound has been studied for its potential role in metal chelation therapy, the treatment of heavy metal poisoning by promoting the excretion of toxic metals in the body.

Thiosalicylic acid and its derivatives have been historically used in photography as components of developer solutions to reduce exposed silver halides to metallic silver during film and paper processing. It is used as a dye auxiliary in the textile industry to help fix dyes on fabrics and improve color fastness.

Thiosalicylic acid is a precursor for the synthesis of various organic compounds, including pharmaceutical intermediates and specialty chemicals. It participates in reactions such as esterification, amidation, and nucleophilic substitution, expanding its use in synthetic organic chemistry.

References

2024. Synthesis, In Silico, and In Vitro Evaluation of the Potential Antioxidant Activity of New Quinazoline Derivatives. Russian Journal of Bioorganic Chemistry, 50, 4.
DOI: 10.1134/s1068162024040228

2024. Development of novel thiazole-based hybrids as DNA gyrase inhibitors: design, synthesis, in silico and in vitro antibacterial evaluation. Journal of the Iranian Chemical Society, 21, 8.
DOI: 10.1007/s13738-024-03011-z

1961. Stimulation of brain respiration by thiosalicylic acid. Biochemical and Biophysical Research Communications, 4, 2.
DOI: 10.1016/0006-291x(61)90250-9