Coumarin

Coumarin is a chemical compound; a toxin found in many plants, notably in high concentration in the tonka bean, woodruff, and bison grass. It has a sweet scent, readily recognised as the scent of newly-mown hay. It has clinical value as the precursor for several anticoagulants, notably warfarin. It is also used as a gain medium in some dye lasers.

The name comes from a French word, coumarou, for the tonka bean.

Synthesis
The biosynthesis of coumarin in plants is via hydroxylation, glycolysis and cyclization of cinnamic acid. Coumarin can be prepared in a laboratory in a Perkin reaction between salicylaldehyde and acetic anhydride.



The Pechmann condensation provides another synthesis of coumarin and its derivatives.

Derivatives
Some naturally occurring coumarin derivatives include umbelliferone (7-hydroxycoumarin), aesculetin (6,7-dihydroxycoumarin), herniarin (7-methoxycoumarin), psoralen and imperatorin. Coumarin and its derivatives are all considered phenylpropanoids.

Coumarin toxicity
Coumarin is often found in tobacco products and artificial vanilla substitutes, though it has been banned as a food additive in numerous countries since the mid-20th century because it is moderately toxic to the liver and kidneys, with an LD50 of 275 mg/kg - low compared to related compounds. Although only somewhat dangerous to humans, coumarin is a potent rodenticide: rats and other rodents largely metabolize it to 3,4-coumarin epoxide, a toxic compound that can cause internal hemorrhage and death. Humans largely metabolize it to 7-hydroxycoumarin, a compound of lower toxicity.

Coumarin was banned as a food additive in the United States in 1978. OSHA considers this compound to be only a lung-specific carcinogen, and "not classifiable as to its carcinogenicity to humans". Coumarin was banned as an adulterant in cigarettes by tobacco companies in 1997, but due to the lack of reporting requirements to the US Department of Health and Human Services it was still being used as a flavoring additive in pipe tobacco. Coumarin is currently listed by the United States Food and Drug Administration (FDA) among "Substances Generally Prohibited From Direct Addition or Use as Human Food", according to 21 CFR 189.130, but some natural additives containing coumarin (such as sweet woodruff) are allowed "in alcoholic beverages only" (21 CFR 172.510 ). In Europe, such beverages are very popular, for example Maiwein (white wine with woodruff) and Żubrówka (vodka flavored with bison grass).

European health agencies have warned against consuming high amounts of cassia bark, one of the four species of cinnamon, because of its coumarin content.

Coumarin should be avoided by people with perfume allergy. Flexitral (Chantilly, VA) has developed an allergen replacement product called Coumane(TM), GRAS. .

Compounds
Compounds within the coumarin family include:
 * brodifacoum,
 * bromadiolone,
 * coumafuryl, and
 * difenacoum.
 * Ensaculin
 * warfarin

Several of the above compounds are used as rodenticides.