Salicylic acid
A molecule with adjacent phenol and carboxylic-acid groups, central to aspirin chemistry.
- Formula
- C7H6O3
- Molar mass
- 138.12 g/mol
- Also known as
- 2-hydroxybenzoic acid, o-hydroxybenzoic acid, 2-Carboxyphenol, o-Carboxyphenol, Retarder W, Rutranex
Overview
A molecule with adjacent phenol and carboxylic-acid groups, central to aspirin chemistry.
The two oxygen-containing groups provide distinct reaction sites. Acetylating the phenolic OH gives aspirin while retaining the carboxylic acid. Tracking which group reacts prevents confusion between aspirin formation and esterification of the carboxyl group to give methyl salicylate.
Identifiers
- Formula
- C7H6O3
- Molar mass
- 138.12 g/mol
- Also known as
- 2-hydroxybenzoic acid, o-hydroxybenzoic acid, 2-Carboxyphenol, o-Carboxyphenol, Retarder W, Rutranex
Chemical identifiers
- SMILES
- C1=CC=C(C(=C1)C(=O)O)O
- InChI
- InChI=1S/C7H6O3/c8-6-4-2-1-3-5(6)7(9)10/h1-4,8H,(H,9,10)
- PubChem CID
- 338
Properties
- Melting Point
- 159 °C
- Boiling Point
- 211 °C at 20 torr
- Density
- 1.443 g/cu cm at 20 °C/4 °C
- Water solubility
- In water, 2,240 mg/L at 25 °C
Diagnostic tests
Iron(III) salicylate colour test
- Reagent
- iron(III) solution from the reference assay
- Conditions
- Compare dissolved sample, salicylic-acid standard and reagent blank under matched conditions.
- Positive observation
- Purple complex colour forms.
- Negative observation
- The blank lacks the purple salicylate colour.
- Interpretation
- The free phenolic group permits coloured complex formation.
- Scope
- Expected positive for salicylic acid.
- Limitations
- pH and concentration affect colour; other coordinating phenols can interfere.
- Evidence
- reference experiment
Related compounds
- Phenols
A molecule with adjacent phenol and carboxylic-acid groups, central to aspirin chemistry.
- Carboxylic acids
A molecule with adjacent phenol and carboxylic-acid groups, central to aspirin chemistry.
Connected reactions
- O acetylation: Salicylic acid → Aspirin
The phenolic oxygen of salicylic acid receives an acetyl group from ethanoic anhydride. Acyl substitution forms an ester while retaining the separate carboxyl group; proton transfer gives ethanoic acid as the co-product.
- Acid hydrolysis: Aspirin → Salicylic acid
Water attacks the acid-activated acetyl carbonyl. Acyl-oxygen cleavage and proton transfer restore the phenolic OH of salicylic acid, while the removed acetyl group becomes ethanoic acid.
- Alkaline hydrolysis and acidification: Methyl salicylate → Salicylic acid
Hydroxide adds at the ester carbonyl and displaces the methoxy fragment, which becomes methanol. Alkaline conditions leave the salicylate groups deprotonated; subsequent acidification restores the neutral acid and phenolic OH.
References
- PubChem Compound Summary: Salicylic acid (CID 338)National Center for Biotechnology Information · PubChem
Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.
- The aspirin storyRoyal Society of Chemistry · RSC Education
Functional-group context for salicylic acid and aspirin; the catalog description is not clinical advice or a medicinal-product specification.
- OpenStax Organic Chemistry: Chemistry of estersJohn McMurry · OpenStax · 2023
Supports the qualitative structural interpretation of the recorded molecular structure; no new physical measurement or verified preparative yield is claimed.
- Hazardous Substances Data Bank (HSDB): Salicylic acid — melting pointHazardous Substances Data Bank (HSDB)
Retrieved through PubChem PUG View on 2026-09-08. https://pubchem.ncbi.nlm.nih.gov/compound/338#section=Melting-Point. Source value, complete property clause or compact miscibility statement retained; absent pressure, temperature or phase conditions are not inferred. Original reference: O'Neil, M.J. (ed.). The Merck Index - An Encyclopedia of Chemicals, Drugs, and Biologicals. Whitehouse Station, NJ: Merck and Co., Inc., 2006., p. 1438
- Hazardous Substances Data Bank (HSDB): Salicylic acid — boiling pointHazardous Substances Data Bank (HSDB)
Retrieved through PubChem PUG View on 2026-09-08. https://pubchem.ncbi.nlm.nih.gov/compound/338#section=Boiling-Point. Source value, complete property clause or compact miscibility statement retained; absent pressure, temperature or phase conditions are not inferred. Original reference: O'Neil, M.J. (ed.). The Merck Index - An Encyclopedia of Chemicals, Drugs, and Biologicals. Whitehouse Station, NJ: Merck and Co., Inc., 2006., p. 1438
- Hazardous Substances Data Bank (HSDB): Salicylic acid — densityHazardous Substances Data Bank (HSDB)
Retrieved through PubChem PUG View on 2026-09-08. https://pubchem.ncbi.nlm.nih.gov/compound/338#section=Density. Source value, complete property clause or compact miscibility statement retained; absent pressure, temperature or phase conditions are not inferred. Original reference: Lide, D.R. CRC Handbook of Chemistry and Physics 86TH Edition 2005-2006. CRC Press, Taylor & Francis, Boca Raton, FL 2005, p. 3-288
- Hazardous Substances Data Bank (HSDB): Salicylic acid — solubilityHazardous Substances Data Bank (HSDB)
Retrieved through PubChem PUG View on 2026-09-08. https://pubchem.ncbi.nlm.nih.gov/compound/338#section=Solubility. Source value, complete property clause or compact miscibility statement retained; absent pressure, temperature or phase conditions are not inferred. Original reference: Yalkowsky SH, Dannenfelser RM; The AQUASOL dATAbASE of Aqueous Solubility. Ver 5. Tucson, AZ: Univ AZ, College of Pharmacy (1992)
- Analysis of aspirin tablets on a microscaleRoyal Society of Chemistry · RSC Education
Source-supported qualitative reference observations.