# Coumarin

**Coumarin** (2H-chromen-2-one, older name 1,2-benzopyrone; C₉H₆O₂; CAS 91-64-5) is a colorless crystalline lactone with the sweet odor of new-mown hay and vanilla, occurring naturally in tonka beans, sweet clover, sweet woodruff, cassia, and lavender, and produced industrially by synthesis.<sup>[1](https://pubchem.ncbi.nlm.nih.gov/compound/323)</sup><sup> • </sup><sup>[2](https://www.ncbi.nlm.nih.gov/books/NBK390898/)</sup> It gives its name to the coumarins, a large class of plant secondary metabolites formed by substitution on the 2H-chromen-2-one skeleton.<sup>[3](https://goldbook.iupac.org/terms/view/C01369)</sup> The name derives from *coumarou*, a French term for the tonka bean.<sup>[4](https://patentimages.storage.googleapis.com/10/6d/be/ef6e902e59f4d3/US11116712.pdf)</sup>

| Key fact | Detail |
|---|---|
| Identity | 2H-chromen-2-one (1,2-benzopyrone), C₉H₆O₂, molecular weight 146.14 g/mol, CAS 91-64-5<sup>[1](https://pubchem.ncbi.nlm.nih.gov/compound/323)</sup> |
| Physical properties | Melting point 70.6 °C; boiling point 297–299 °C; colorless crystals with a sweet, hay- and vanilla-like odor and a bitter aromatic burning taste<sup>[5](https://ntp.niehs.nih.gov/sites/default/files/ntp/htdocs/lt_rpts/tr422.pdf)</sup><sup> • </sup><sup>[1](https://pubchem.ncbi.nlm.nih.gov/compound/323)</sup> |
| First isolation | Extracted from tonka beans (*Dipteryx odorata*) by Vogel in 1820<sup>[2](https://www.ncbi.nlm.nih.gov/books/NBK390898/)</sup> |
| First synthesis | Perkin, 1868, heating the sodium salt of salicylaldehyde with acetic anhydride<sup>[6](https://www.mdpi.com/2304-6740/10/2/23)</sup> |
| Natural content | Tonka beans contain 1–3% coumarin by weight, in rare cases up to 10%; cinnamon leaf oil about 40,600 mg/kg, cassia leaf oil 17,000–87,300 mg/kg<sup>[7](https://doi.org/10.1007/s00217-024-04648-z)</sup><sup> • </sup><sup>[2](https://www.ncbi.nlm.nih.gov/books/NBK390898/)</sup> |
| Food regulation | Prohibited as a direct food additive in the United States since 1954 (21 CFR 189.130); the EU sets maximum levels of 5–50 mg/kg in cinnamon-containing foods<sup>[8](https://www.law.cornell.edu/cfr/text/21/189.130)</sup><sup> • </sup><sup>[9](https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX%3A02008R1334-20230321)</sup> |
| Tolerable intake | EFSA tolerable daily intake of 0–0.1 mg/kg body weight, based on a NOAEL of 10 mg/kg bw/day for liver toxicity in a two-year dog study<sup>[10](https://www.efsa.europa.eu/sites/default/files/event/afc041005-m.pdf)</sup> |

## Chemistry and physical properties

Coumarin is a benzopyrone: a benzene ring fused to an α-pyrone ring, with the keto group at the 2-position of the chromene skeleton.<sup>[1](https://pubchem.ncbi.nlm.nih.gov/compound/323)</sup><sup> • </sup><sup>[3](https://goldbook.iupac.org/terms/view/C01369)</sup> It is a lactone, the intramolecular ester of *o*-hydroxycinnamic acid (coumarinic acid), and the lactone ring is easily hydrolyzed to salts of coumarinic acid.<sup>[1](https://pubchem.ncbi.nlm.nih.gov/compound/323)</sup> The compound dissolves sparingly in cold water, 1 g in about 400 mL, and more readily in boiling water, 1 g in 50 mL.<sup>[1](https://pubchem.ncbi.nlm.nih.gov/compound/323)</sup>

## Natural occurrence

Coumarin was first isolated by Vogel in 1820 from tonka beans (*Dipteryx odorata*), a tropical tree of Central and South America, and was subsequently identified in plants of many families: sweet clover (*Melilotus alba* and *M. officinalis*), sweet woodruff (*[Asperula odorata](https://www.edgepedia.org/galium-odoratum)*), vanilla leaf (*Trilisa odoratissima*), vanilla beans, cassia (*Cinnamomum cassia*), lavender, and balsam of Peru, as well as legumes, orchids, grasses, and citrus fruits.<sup>[2](https://www.ncbi.nlm.nih.gov/books/NBK390898/)</sup> It reaches particularly high levels in some essential oils: cinnamon leaf oil at about 40,600 mg/kg, cinnamon bark oil at 7,000 mg/kg, cassia leaf oil at 17,000–87,300 mg/kg, and lavender oil.<sup>[2](https://www.ncbi.nlm.nih.gov/books/NBK390898/)</sup> Lower levels occur in green tea (0.2–1.7 ppm), bilberry, cloudberry, chicory root, strawberries, apricots, cherries, carrots, celery, peppermint, honey, beer, wine, and tobacco.<sup>[2](https://www.ncbi.nlm.nih.gov/books/NBK390898/)</sup><sup> • </sup><sup>[1](https://pubchem.ncbi.nlm.nih.gov/compound/323)</sup>

In plants, coumarins are phenylpropanoid-derived secondary metabolites. They contribute to defense against pathogens: coumarins disrupt pathogen cell membranes, inhibit enzymatic activity, hinder nucleic acid synthesis, and stimulate plant immune responses including reactive oxygen species production and salicylic-acid-dependent signaling.<sup>[11](https://pubmed.ncbi.nlm.nih.gov/39374740/)</sup> At least 1,300 coumarin derivatives, free and as glucosides, have been identified in green plants.<sup>[2](https://www.ncbi.nlm.nih.gov/books/NBK390898/)</sup>

## History and synthesis

**Perkin synthesis.** In 1868 [William Henry Perkin](https://www.edgepedia.org/william-henry-perkin) heated the sodium salt of salicylaldehyde with acetic anhydride and obtained a product identical to the natural substance, the first artificial synthesis of coumarin; further development of the process produced the general Perkin reaction for cinnamic acid analogs.<sup>[6](https://www.mdpi.com/2304-6740/10/2/23)</sup><sup> • </sup><sup>[12](https://pubs.rsc.org/en/content/articlelanding/1868/js/js8682100053)</sup>

**Pechmann condensation.** In 1883 the German chemist Hans von Pechmann reported the condensation of phenols with carboxylic acids or esters containing a β-carbonyl group, which yields coumarins under acidic catalysis.<sup>[13](https://www.sciencedirect.com/science/chapter/bookseries/pii/B9780128001714000019)</sup> The reaction remains one of the most widely used routes to coumarin derivatives, run with Brønsted acids such as sulfuric or trifluoroacetic acid, Lewis acids such as AlCl₃, ZnCl₂, ZrCl₄, and TiCl₄, or heterogeneous catalysts including ion-exchange resins and zeolites.<sup>[13](https://www.sciencedirect.com/science/chapter/bookseries/pii/B9780128001714000019)</sup><sup> • </sup><sup>[6](https://www.mdpi.com/2304-6740/10/2/23)</sup> Other classical routes include the [Knoevenagel condensation](https://www.edgepedia.org/knoevenagel-condensation), [Reformatsky reaction](https://www.edgepedia.org/reformatsky-reaction), [Wittig reaction](https://www.edgepedia.org/wittig-reaction), and Claisen rearrangement.<sup>[13](https://www.sciencedirect.com/science/chapter/bookseries/pii/B9780128001714000019)</sup> Commercial coumarin has been produced synthetically for many years rather than extracted from plants.<sup>[2](https://www.ncbi.nlm.nih.gov/books/NBK390898/)</sup>

## Fragrance and industrial uses

Because of its sweet, hay-like note and stability, coumarin has been an important perfumery raw material since 1882, acting as a fixative and odor enhancer in fern (fougère) and Chypre-type fragrances and in combination with lavender, citrus, rosemary, and oakmoss.<sup>[14](https://pmc.ncbi.nlm.nih.gov/articles/PMC7278589/)</sup><sup> • </sup><sup>[2](https://www.ncbi.nlm.nih.gov/books/NBK390898/)</sup> It is used in hand soaps, detergents, lotions, and perfumes at concentrations usually between 0.01% and 0.8%, and in a wide range of cosmetics including shampoos, toothpaste, deodorants, sunscreens, and lipsticks.<sup>[2](https://www.ncbi.nlm.nih.gov/books/NBK390898/)</sup><sup> • </sup><sup>[14](https://pmc.ncbi.nlm.nih.gov/articles/PMC7278589/)</sup> Formerly large quantities went into food flavoring, often with vanillin, for chocolates, baked goods, and cream-soda beverages.<sup>[2](https://www.ncbi.nlm.nih.gov/books/NBK390898/)</sup> Non-fragrance uses include tobacco flavoring, an electroplating adjuvant for brightening chrome-plated steel, and intermediates such as dihydrocoumarin.<sup>[14](https://pmc.ncbi.nlm.nih.gov/articles/PMC7278589/)</sup><sup> • </sup><sup>[2](https://www.ncbi.nlm.nih.gov/books/NBK390898/)</sup><sup> • </sup><sup>[15](https://s3.amazonaws.com/NARAprodstorage/lz/electronic-records/rg-081/ITC/pub2852.pdf)</sup>

## Toxicology and regulation

**Food.** Coumarin causes liver toxicity in rats and dogs, and on that basis the United States withdrew it from use as a direct food additive in 1954; under 21 CFR 189.130, food containing any added coumarin, or coumarin as a constituent of tonka beans or tonka extract, is deemed adulterated.<sup>[14](https://pmc.ncbi.nlm.nih.gov/articles/PMC7278589/)</sup><sup> • </sup><sup>[8](https://www.law.cornell.edu/cfr/text/21/189.130)</sup> In the European Union, Regulation (EC) No 1334/2008 prohibits adding coumarin as such but sets maximum levels for cinnamon-containing foods: 50 mg/kg in traditional and seasonal bakery ware labeled as containing cinnamon, 20 mg/kg in breakfast cereals including muesli, 15 mg/kg in other fine bakery ware, and 5 mg/kg in desserts.<sup>[9](https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX%3A02008R1334-20230321)</sup> The European Food Safety Authority set a tolerable daily intake of 0–0.1 mg/kg body weight, applying a safety factor of 100 to a NOAEL of 10 mg/kg bw/day for hepatotoxicity in the most sensitive animal species, the dog.<sup>[10](https://www.efsa.europa.eu/sites/default/files/event/afc041005-m.pdf)</sup> The greatest dietary contribution comes from cinnamon and cinnamon-containing foods.<sup>[14](https://pmc.ncbi.nlm.nih.gov/articles/PMC7278589/)</sup>

**Metabolism.** In humans, coumarin 7-hydroxylation is catalyzed by a high-affinity CYP2A6 enzyme in liver microsomes, and CYP2A6 is the only enzyme catalyzing this reaction, so formation of 7-hydroxycoumarin serves as an in vitro and in vivo probe for CYP2A6 activity.<sup>[16](https://pubmed.ncbi.nlm.nih.gov/10781881/)</sup> Species differences in coumarin metabolism underlie the differing toxicity patterns: rats are particularly susceptible to liver effects and mice to lung effects.<sup>[17](https://pubmed.ncbi.nlm.nih.gov/16203076/)</sup>

**Topical products.** The Australian Therapeutic Goods Administration's 2019 safety review identified concerns of liver injury, skin sensitization, and risk to children, and set a tolerable daily limit of 0.1 mg/kg body weight from all sources; topical listed medicines are limited to 0.001% coumarin, and sunscreens containing it must be labeled for adult use only.<sup>[18](https://www.tga.gov.au/resources/publication/corporate-reports/safety-review-coumarin-topical-listed-medicines)</sup> Coumarin penetrates human skin rapidly and efficiently, with dermal absorption of 60–100% reported for the fragrance compound.<sup>[2](https://www.ncbi.nlm.nih.gov/books/NBK390898/)</sup><sup> • </sup><sup>[19](https://pmc.ncbi.nlm.nih.gov/articles/PMC6044641/)</sup>

## Coumarin derivatives in medicine and agriculture

The 4-hydroxycoumarin derivatives are vitamin K antagonists. In the 1920s, cattle in North America developed a fatal hemorrhagic disease traced to moldy sweet clover hay: as the clover spoils, fungi convert its coumarin to dicumarol, a potent anticoagulant that blocks regeneration of vitamin K from its 2,3-epoxide, reducing production of the vitamin K-dependent clotting factors II, VII, IX, and X.<sup>[20](https://www.merckvetmanual.com/toxicology/moldy-sweet-clover-poisoning/moldy-sweet-clover-poisoning-in-animals)</sup> Dicumarol concentrations of 20–30 mg/kg of hay ingested over several weeks usually cause poisoning in cattle; treatment is removal of the feed, blood transfusion, and vitamin K₁.<sup>[20](https://www.merckvetmanual.com/toxicology/moldy-sweet-clover-poisoning/moldy-sweet-clover-poisoning-in-animals)</sup> This line of chemistry produced warfarin, a coumarin derivative prescribed at low doses as a blood thinner, which acts by interfering with the cyclic interconversion of vitamin K and its 2,3-epoxide.<sup>[13](https://www.sciencedirect.com/science/chapter/bookseries/pii/B9780128001714000019)</sup><sup> • </sup><sup>[21](https://www.ahajournals.org/doi/pdf/10.1161/01.cir.0000063575.17904.4e)</sup> Coumarin derivatives are also used as anticoagulant rodenticides.<sup>[20](https://www.merckvetmanual.com/toxicology/moldy-sweet-clover-poisoning/moldy-sweet-clover-poisoning-in-animals)</sup>

## Fluorescence and optical applications

The parent compound itself is a poor fluorophore: unsubstituted coumarin exhibits zero or very weak fluorescence.<sup>[22](https://pmc.ncbi.nlm.nih.gov/articles/PMC6268095/)</sup> Properly substituted derivatives, particularly those with electron-donating groups at positions 6 and 7 that create a push-pull system with the lactone carbonyl, yield intense fluorescence and are widely used as fluorescent probes, sensors, laser dyes, optical brighteners, and dyes for dye-sensitized solar cells.<sup>[22](https://pmc.ncbi.nlm.nih.gov/articles/PMC6268095/)</sup><sup> • </sup><sup>[23](https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/ejoc.202001658)</sup> Because coumarin fluorescence is sensitive to solvent polarity and micro-viscosity, coumarin derivatives serve as environment-sensitive probes in chemistry, biology, and polymer science.<sup>[22](https://pmc.ncbi.nlm.nih.gov/articles/PMC6268095/)</sup>

## References

1. [Coumarin, CID 323, PubChem](https://pubchem.ncbi.nlm.nih.gov/compound/323)
2. [Coumarin, IARC Monographs Volume 77 (NCBI Bookshelf)](https://www.ncbi.nlm.nih.gov/books/NBK390898/)
3. [Coumarins, IUPAC Gold Book C01369](https://goldbook.iupac.org/terms/view/C01369)
4. [US Patent 11,116,712 B2](https://patentimages.storage.googleapis.com/10/6d/be/ef6e902e59f4d3/US11116712.pdf)
5. [NTP Technical Report 422: Toxicology and Carcinogenesis Studies of Coumarin](https://ntp.niehs.nih.gov/sites/default/files/ntp/htdocs/lt_rpts/tr422.pdf)
6. [Coumarins Synthesis and Transformation via C–H Bond Activation—A Review, Inorganics (MDPI)](https://www.mdpi.com/2304-6740/10/2/23)
7. [Coumarin contents of tonka (Dipteryx odorata) products, European Food Research and Technology](https://doi.org/10.1007/s00217-024-04648-z)
8. [21 CFR § 189.130 Coumarin, Legal Information Institute](https://www.law.cornell.edu/cfr/text/21/189.130)
9. [Regulation (EC) No 1334/2008, consolidated text, EUR-Lex](https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX%3A02008R1334-20230321)
10. [AFC Panel minutes, 8th plenary meeting, EFSA (2004)](https://www.efsa.europa.eu/sites/default/files/event/afc041005-m.pdf)
11. [Toxicity of coumarins in plant defense against pathogens, PubMed](https://pubmed.ncbi.nlm.nih.gov/39374740/)
12. [Perkin, W. H. (1868). On the artificial production of coumarin, J. Chem. Soc.](https://pubs.rsc.org/en/content/articlelanding/1868/js/js8682100053)
13. [Pechmann Reaction in the Synthesis of Coumarin Derivatives, Advances in Heterocyclic Chemistry](https://www.sciencedirect.com/science/chapter/bookseries/pii/B9780128001714000019)
14. [Coumarins in Food and Methods of Their Determination, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC7278589/)
15. [Physical Characteristics and Uses, US International Trade Commission Publication 2852](https://s3.amazonaws.com/NARAprodstorage/lz/electronic-records/rg-081/ITC/pub2852.pdf)
16. [CYP2A6: a human coumarin 7-hydroxylase, PubMed](https://pubmed.ncbi.nlm.nih.gov/10781881/)
17. [A safety assessment of coumarin taking into account species-specificity of toxicokinetics, PubMed](https://pubmed.ncbi.nlm.nih.gov/16203076/)
18. [Safety review of coumarin in topical listed medicines, Therapeutic Goods Administration](https://www.tga.gov.au/resources/publication/corporate-reports/safety-review-coumarin-topical-listed-medicines)
19. [Bioprofiling of Cosmetics with Focus on Streamlined Coumarin Analysis, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC6044641/)
20. [Moldy Sweet Clover Poisoning in Animals, Merck Veterinary Manual](https://www.merckvetmanual.com/toxicology/moldy-sweet-clover-poisoning/moldy-sweet-clover-poisoning-in-animals)
21. [AHA/ACC Guide to Warfarin Therapy, Circulation](https://www.ahajournals.org/doi/pdf/10.1161/01.cir.0000063575.17904.4e)
22. [Spectral Properties of Substituted Coumarins in Solution and Polymer Matrices, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC6268095/)
23. [Prevalent Bioimaging Scaffolds, European Journal of Organic Chemistry](https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/ejoc.202001658)

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*Topic: Encyclopedia › Physical world and mathematics › Chemistry › Organic substances › Carbonyl and carboxyl chemistry › Carboxylic acid derivatives › Esters › Esters by acyl residue*

*Initially written Sep 17, 2026 · Reviewed: Sep 30, 2026; Oct 15, 2026 · Edited: Sep 30, 2026; Oct 15, 2026 · Last review: Oct 15, 2026*

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License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license