Aspirin

Acetylsalicylic acid: an ester and a carboxylic acid in the same molecule.

Formula
C9H8O4
Molar mass
180.16 g/mol
Also known as
2-acetyloxybenzoic acid, ACETYLSALICYLIC ACID, 2-Acetoxybenzoic acid, 2-(Acetyloxy)benzoic acid, Acylpyrin, O-Acetylsalicylic acid, o-Acetoxybenzoic acid

Overview

Acetylsalicylic acid: an ester and a carboxylic acid in the same molecule.

Aspirin forms by acetylation of salicylic acid’s phenolic OH. Its carboxyl group gives acid–base behaviour, ester hydrolysis regenerates salicylic acid, and melting range or chromatography assesses purity.

Identifiers

Formula
C9H8O4
Molar mass
180.16 g/mol
Also known as
2-acetyloxybenzoic acid, ACETYLSALICYLIC ACID, 2-Acetoxybenzoic acid, 2-(Acetyloxy)benzoic acid, Acylpyrin, O-Acetylsalicylic acid, o-Acetoxybenzoic acid
Chemical identifiers
SMILES
CC(=O)OC1=CC=CC=C1C(=O)O
InChI
InChI=1S/C9H8O4/c1-6(10)13-8-5-3-2-4-7(8)9(11)12/h2-5H,1H3,(H,11,12)
PubChem CID
2244

Properties

Melting Point
135 °C (rapid heating)
Boiling / decomposition
284 °F at 760 mmHg (decomposes) (NTP, 1992)
Density
1.4 g/cm³
Water solubility
In water, 4,600 mg/L at 25 °C

Diagnostic tests

Free salicylic-acid impurity check

Reagent
iron(III) solution from the reference assay
Conditions
Use a fresh sample solution and matched salicylic-acid standards.
Positive observation
Purple colour indicates free salicylate in the tested sample.
Negative observation
Fresh aspirin with no detectable salicylate gives no corresponding purple colour.
Interpretation
Salicylate can reflect incomplete acetylation or subsequent aspirin hydrolysis.
Scope
Aspirin impurity test.
Limitations
Compare the visual observation with calibrated measurements and sample conditions.
Evidence
reference experiment

Related compounds

  • Esters

    Acetylsalicylic acid: an ester and a carboxylic acid in the same molecule.

  • Carboxylic acids

    Acetylsalicylic acid: an ester and a carboxylic acid in the same molecule.

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.

References

  1. PubChem Compound Summary: Aspirin (CID 2244)National Center for Biotechnology Information · PubChem

    Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.

  2. 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.

  3. Hazardous Substances Data Bank (HSDB): Aspirin — melting pointHazardous Substances Data Bank (HSDB)

    Retrieved through PubChem PUG View on 2026-09-08. https://pubchem.ncbi.nlm.nih.gov/compound/2244#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. 140

  4. CAMEO Chemicals: Aspirin — boiling pointCAMEO Chemicals

    Retrieved through PubChem PUG View on 2026-09-08. https://pubchem.ncbi.nlm.nih.gov/compound/2244#section=Boiling-Point. Source value, complete property clause or compact miscibility statement retained; absent pressure, temperature or phase conditions are not inferred. Original reference: National Toxicology Program, Institute of Environmental Health Sciences, National Institutes of Health (NTP). 1992. National Toxicology Program Chemical Repository Database. Research Triangle Park, North Carolina.

  5. ILO-WHO International Chemical Safety Cards (ICSCs): Aspirin — densityILO-WHO International Chemical Safety Cards (ICSCs)

    Retrieved through PubChem PUG View on 2026-09-08. https://pubchem.ncbi.nlm.nih.gov/compound/2244#section=Density. Source value, complete property clause or compact miscibility statement retained; absent pressure, temperature or phase conditions are not inferred.

  6. Hazardous Substances Data Bank (HSDB): Aspirin — solubilityHazardous Substances Data Bank (HSDB)

    Retrieved through PubChem PUG View on 2026-09-08. https://pubchem.ncbi.nlm.nih.gov/compound/2244#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; Aquasol Database of Aqueous Solubility. Version 5. College of Pharmacy, University of Arizona - Tucson, AZ (1992)

  7. Analysis of aspirin tablets on a microscaleRoyal Society of Chemistry · RSC Education

    Source-supported qualitative reference observations.