Title: Azulene
CAS Registry Number: 275-51-4
CAS Name: Cyclopentacycloheptene
Additional Names: bicyclo-[5.3.0]-deca-2,4,6,8,10-pentaene; bicyclo-[0.3.5]-deca-1,3,5,7,9-pentaene
Molecular Formula: C10H8
Molecular Weight: 128.17
Percent Composition: C 93.71%, H 6.29%
Literature References: Prepn from octahydronaphthalene: Plattner, Pfau, Helv. Chim. Acta 20, 224 (1937); from indan: Plattner, Magyar, ibid. 25, 581 (1942).
Properties: Intensely blue leaflets or monoclinic plates from alc. Odor of naphthalene. mp 98.5-99°. Absorption spectrum: Susz et al., Helv. Chim. Acta 20, 469 (1937); Plattner, ibid. 24, 283 (1941). Insol in water; sol in the usual organic solvents, in concd mineral acids with decompn.
Melting point: mp 98.5-99°
Derivative Type: Sodium sulfonate
CAS Registry Number: 51873-93-9
Trademarks: Azunol (Nippon Shinyaku); Azusalen (Ohta)
Therap-Cat: Sodium sulfonate as antacid.
Keywords: Antacid.
Azure B Azure C Babbitt Metal Bacampicillin Bacillus thuringiensis

Azulen num.svg Azulene 3d structure.png
CAS number 275-51-4 YesY
PubChem 9231
ChemSpider 8876 YesY
KEGG C13392 YesY
ChEBI CHEBI:31249 YesY
Jmol-3D images Image 1
Molecular formula C10H8
Molar mass 128.17 g mol−1
Melting point 99–100 °C
Boiling point 242 °C
Solubility in water 0.02 g/l[1]
Std enthalpy of
combustion ΔcHo298
−1266.5 kcal/mol[2]
 YesY (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references

Azulene is an organic compound and an isomer of naphthalene. Whereas naphthalene is colourless, azulene is dark blue. Its name is derived from the Spanish word azul, meaning "blue". Two terpenoids, vetivazulene (4,8-dimethyl-2-isopropylazulene) and guaiazulene (1,4-dimethyl-7-isopropylazulene), that feature the azulene skeleton are found in nature as constituents of pigments in mushrooms, guaiac wood oil, and some marine invertebrates.

Azulene has a long history, dating back to the 15th century as the azure-blue chromophore obtained by steam distillation of German chamomile. The chromophore was discovered in yarrow and wormwood and named in 1863 by Septimus Piesse. Its structure was first reported by Lavoslav Ružička, followed by its organic synthesis in 1937 by Placidus Plattner.