ImageFile = Azulene-numbers.png
ImageSize = 200px
IUPACName = bicyclo [5.3.0] decapentaene
Section1 = Chembox Identifiers
CASNo = 275-51-4
SMILES = C12=CC=CC=CC1=CC=C2
Section2 = Chembox Properties
MeltingPt = 99 - 100 °C
BoilingPt = 242 °C
Section3 = Chembox Hazards
Azulene is an
organic compoundand a monoterpene. It is an isomer of naphthalenebut its physical properties are quite different. Naphthalene is a white crystalline solid whereas azulene, whose name is derived from the Spanish word azul, meaning "blue", is a dark blue crystalline solid used in many cosmetics. Azulene has a long history dating back to the 15th century as the azure-blue distillate obtained by steam distillationof Chamomile. The compound was discovered and named in 1863 by Septimus Piesse in azure-blue distillates from other sources such as yarrowand wormwood. Lavoslav Ružičkasolved the structure for this compound and the first organic synthesisfollowed in 1937 by Placidus Plattner.
Vetivazuleneor 4,8-dimethyl-2-isopropylazulene is obtained from vetiveroil. Guaiazuleneor 1,4-dimethyl-7-isopropylazulene occurs naturally as a constituent of guaiac wood oil.
Azulene consists of a fused
cyclopentadienering and a cycloheptatrienering and is an isomer of naphthalene. Azulene is 10 pi electronsystem just like cyclodecapentaeneand does have aromaticproperties even though it is not a single ring system like benzene. The peripheral bonds have similar lengths and only the shared bond in the middle is a single bond. The stability gain from aromaticity is half of that of naphthalene. The molecule can be considered a fusion product of a 6 pi electron cyclopentadienyl anionwhich is aromatic and the likewise aromatic 6 pi electron tropylium cation. The observed dipole momentof 0.8 Debye(very different from naphthalene, which has zero dipole moment) is consistent with this picture.
For many years not many synthetic routes existed to azulene and the compound was therefore expensive. A recent contribution takes
cycloheptatrieneas starting material ["Approach to the Blues: A Highly Flexible Route to the Azulenes" Sébastien Carret, Aurélien Blanc, Yoann Coquerel, Mikaël Berthod, Andrew E. Greene, Jean-Pierre Deprés Angewandte Chemie International EditionVolume 44, Issue 32 , Pages 5130 - 5133 2005 [http://www3.interscience.wiley.com/cgi-bin/abstract/110567907/ABSTRACT Abstract] ] .
cycloheptatriene2+2 cycloadditionwith dichloro ketenestep 2: diazomethane insertion reactionstep 3: dehydrohalogenationreaction with DMF step 4: carbonylreduction to alcoholwith sodium borohydridestep 5: elimination reactionwith Burgess reagentstep 6: oxidation with p-chloranilstep 7: dehalogenationwith PMHS, palladium(II) acetate, potassium phosphateand the DPDB ligand]
In naphth [a] azulenes, a
naphthalenering is condensed with the 1,2-position of an azulene ring. In one such system ["Novel Synthesis of Benzalacetone Analogues of Naphth [a] azulenes by Intramolecular Tropylium Ion-Mediated Furan Ring-Opening Reaction and X-ray Investigation of a Naphth [1,2-a] azulene Derivative" Kimiaki Yamamura, Shizuka Kawabata, Takatomo Kimura, Kazuo Eda, and Masao Hashimoto J. Org. Chem.; 2005; 70(22) pp 8902 - 8906; (Article) DOI: 10.1021/jo051409f [http://pubs3.acs.org/acs/journals/doilookup?in_doi=10.1021/jo051409f Abstract] ] deformation from planarity is found similar to that of tetrahelicene.
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