AZULENE

Azulene is a distinctive blue aromatic hydrocarbon valued for its unique fused-ring structure and unusual electronic properties.
Azulene is used in organic synthesis, spectroscopy, functional materials, dyes, and specialty chemical research.
Azulene's derivatives are also important in cosmetic, pharmaceutical, and advanced molecular applications.

CAS Number: 275-51-4
EC Number: 205-993-6
Chemical Formula: C10H8
Molar Mass: 128.174 g/mol

Synonyms: azulene, 275-51-4, Cyclopentacycloheptene, Azunamic, Bicyclo[5.3.0]decapentaene, azulen, Bicyclo(5.3.0)decapentaene, Bicyclo(5.3.0)-deca-2,4,6,8,10-pentaene, 82R6M9MGLP, Bicyclo(5.3.0)-1,3,5,7,9-decapentaene, DTXSID2059770, NSC-89248, CHEBI:31249, RefChem:116159, DTXCID7037686, 205-993-6, EINECS 205-993-6, MFCD00003810, AZULENE [MI], Azulene (JAN), Bicyclo[5.3.0]-1,5,7,9-decapentaene, AZULENE [JAN], C13408, SR-01000944574-1, BICYCLO-(5.3.0)-DECA-2,4,6,8,10-PENTAENE, NSC 89248, UNII-82R6M9MGLP, Azulene (Standard), Azulene, 99%, AZULENE [INCI], bicyclo(5.3.0)-, AZULENE [MART.], AZULENE [WHO-DD], SCHEMBL8463, Azulene, analytical standard, SCHEMBL26516, SCHEMBL183516, SCHEMBL195477, SCHEMBL348614, Azusalen [as sodium sulfonate], orb1299207, SCHEMBL1510123, SCHEMBL1968724, SCHEMBL5586324, SCHEMBL7190249, SCHEMBL9381015, CHEMBL3272628, SCHEMBL23805068, HY-B0055R, HY-B0055, NSC89248, SBB056611, AKOS015840881, EBC-616622, FC66428, CS-15638, SY049872, DB-047243, A0634, Bicyclo(0.3.5)deca-1,3,5,7,9-pentaene, CS-0006517, NS00013373, ST50411971, T8116, Azulene, standard for GC, >=99.0% (GC), bicyclo[5.3.0]deca-2,4,6,8,10-pentaene, D09768, F799019, Q144362, SR-01000944574, J-016811, BICYCLO-(0.3.5)-DECA-1,3,5,7,9-PENTAENE, InChI=1/C10H8/c1-2-5-9-7-4-8-10(9)6-3-1/h1-8, 82451-56-7

Azulene is a mancude carbobicyclic parent consisting of a cycloheptatriene and cyclopentadiene rings.
Azulene has a role as a volatile oil component and a plant metabolite.

Azulene is an ortho-fused bicyclic arene, a member of azulenes and a mancude carbobicyclic parent.
Azulene is a bicyclic aromatic hydrocarbon composed of fused five-membered and seven-membered rings, giving it a distinctive deep blue color.

Unlike its isomer naphthalene, azulene has an unusual electronic structure and a significant dipole moment, which contribute to its unique optical and chemical properties.
Azulene is used in organic synthesis, spectroscopy, functional materials research, dyes, and as a structural motif in pharmaceutical and cosmetic chemistry.

Azulene is an aromatic organic compound and an isomer of naphthalene.
Naphthalene is colourless, whereas azulene is dark blue.

Azulene is named after its colour, as "azul" is Spanish for 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.
Azulene's structure was first reported by Lavoslav Ružička, followed by its organic synthesis in 1937 by Placidus Plattner.

Azulene is a heterocyclic organic compound, and it gives a cosmetic product a blue tint.
Azulene can be found in higher concentrations in chamomile, but it can also be synthesized.

Azulene is one of over 100 different polycyclic aromatic hydrocarbons (PAHs).
PAHs are chemicals that are formed during the incomplete burning organic substances, such as fossil fuels.
They are usually found as a mixture containing two or more of these compounds.

Derivatives of Azulene:
1-Hydroxyazulene is an unstable green oil and it does not show keto–enol tautomerism.
2-Hydroxyazulene is obtained by hydrolysis of 2-methoxyazulene with hydrobromic acid.

Azulene is stable and does show keto–enol tautomerism.
The pKa of 2-hydroxyazulene in water is 8.71.

Azulene is more acidic than phenol or naphthol.
The pKa of 6-hydroxyazulenes in water is 7.38 making it also more acidic than phenol or naphthol.

In naphth[a]azulene, a naphthalene ring is condensed at the 1,2-positions of azulene.
In one such system deviation from planarity is found, similar to that of tetrahelicene.

Guaiazulene (1,4-dimethyl-7-isopropylazulene) is an alkylated derivative of azulene with an almost identical intensely blue colour.
Azulene is commercially available to the cosmetics industry where it functions as a skin conditioning agent.

Uses of Azulene:
Like the parent plant chamomile, Azulene has anti-inflammatory, soothing, and calming properties.
Azulene has non-comedogenic properties, making it beneficial for sensitive and very dry skin.

Azulene can also be used in eye preparation and aftershave.
Azulene is used in organic synthesis as a building block for pharmaceuticals, dyes, pigments, and functional aromatic compounds.

Azulene is also applied in spectroscopy, optoelectronic materials, molecular sensors, and research involving unusual aromatic and electronic behavior.
Azulene derivatives are additionally used in cosmetic and personal-care formulations, especially in soothing and skin-conditioning products.

Structure and Bonding of Azulene:
Azulene is usually viewed as resulting from fusion of cyclopentadiene and cycloheptatriene rings.
Like naphthalene and cyclodecapentaene, Azulene is a 10 pi electron system.

IAzulene exhibits aromatic properties: (i) the peripheral bonds have similar lengths and (ii) it undergoes Friedel-Crafts-like substitutions.
The stability gain from aromaticity is estimated to be half that of naphthalene.

Azulene's dipole moment is 1.08 D in contrast with naphthalene, which has a dipole moment of zero.
This polarity can be explained by regarding azulene as the fusion of a 6 π-electron cyclopentadienyl anion and a 6 π-electron tropylium cation: one electron from the seven-membered ring is transferred to the five-membered ring to give each ring aromatic stability by Hückel's rule.
Reactivity studies confirm that seven-membered ring is electrophilic and the five-membered ring is nucleophilic.

The dipolar nature of the ground state is reflected in its deep colour, which is unusual for small unsaturated aromatic compounds.
Another notable feature of azulene is that it violates Kasha's rule by exhibiting fluorescence from an upper-excited state (S2 → S0).

Organic Synthesis of Azulene:
Synthetic routes to azulene have long been of interest because of its unusual structure.
In 1939 the first method was reported by St. Pfau and Plattner starting from indane and ethyl diazoacetate.

An efficient one-pot route entails annulation of cyclopentadiene with unsaturated C5-synthons.

Procedure:
cycloheptatriene 2+2 cycloaddition with dichloro ketene
diazomethane insertion reaction
dehydrohalogenation reaction with DMF
Luche reduction to alcohol with sodium borohydride
elimination reaction with Burgess reagent
oxidation with p-chloranil
dehalogenation with polymethylhydrosiloxane, palladium(II) acetate, potassium phosphate and the DPDB ligand (BINAP)

Another synthesis route starts by treating pyridinium or pyrylium salts with cyclopentadienyl anion.

Azulene can also be synthesized via a Diels Alder and retro-Diels Alder reaction.
The starting material of the above reaction can be generated through the flash vacuum pyrolysis of phenyl propiolate.

Organometallic Complexes of Azulene:
In organometallic chemistry, azulene serves as a ligand for low-valent metal centers.
Illustrative complexes are (azulene)Mo2(CO)6 and (azulene)Fe2(CO)5.

Stability and Reactivity of Azulene:

Chemical Stability:
Stable under normal ambient and recommended storage conditions.

Reactivity:
No hazardous reactions are expected under normal conditions of use.

Conditions to Avoid:
Excessive heat, ignition sources, and prolonged exposure to incompatible materials.

Incompatible Materials:
Strong oxidizing agents.

Hazardous Decomposition Products:
Thermal decomposition or combustion may generate carbon monoxide, carbon dioxide, and irritating organic fumes.

Handling and Storage of Azulene:

Safe Handling:
Avoid breathing dust and prevent unnecessary contact with skin and eyes.
Handle with adequate ventilation and appropriate personal protective equipment.

Storage Conditions:
Keep the container tightly closed in a cool, dry, and well-ventilated area away from heat and incompatible materials.

First Aid Measures of Azulene:

Inhalation:
Move the affected person to fresh air and obtain medical attention if symptoms occur.

Skin Contact:
Wash thoroughly with plenty of water and remove contaminated clothing.

Eye Contact:
Rinse cautiously with water for at least 15 minutes and seek medical attention.

Ingestion:
Do not induce vomiting; obtain medical attention and treat symptomatically.

Firefighting Measures of Azulene:

Suitable Extinguishing Media:
Use water spray, carbon dioxide, dry chemical, or alcohol-resistant foam.

Specific Hazards:
Combustion may produce irritating fumes and carbon oxides.

Protective Equipment:
Firefighters should wear suitable protective clothing and self-contained breathing apparatus when necessary.

Accidental Release Measures of Azulene:

Personal Precautions:
Ensure adequate ventilation, avoid dust formation, and wear suitable protective equipment.

Environmental Precautions:
Prevent release into drains, waterways, or the surrounding environment.

Cleanup Methods:
Carefully sweep or collect spilled material and place it in a suitable closed container for disposal.

Exposure Controls/Personal Protection of Azulene:

Engineering Controls:
Use adequate general or local exhaust ventilation.

Eye Protection:
Wear safety glasses or chemical goggles.

Hand Protection:
Wear suitable protective gloves.

Skin Protection:
Wear appropriate protective clothing.

Respiratory Protection:
Use suitable particulate respiratory protection where dust exposure cannot be adequately controlled.

Identifiers of Azulene:
CAS Number: 275-51-4
Chem/IUPAC Name: Bicyclo[5.3.0]decapentaene
EINECS/ELINCS No: 205-993-6
COSING REF No: 74540

CAS Number: 275-51-4
ChEBI: CHEBI:31249
ChemSpider: 8876
ECHA InfoCard: 100.005.449
KEGG: C13392
PubChem CID: 9231
UNII: 82R6M9MGLP
CompTox Dashboard (EPA): DTXSID2059770
InChI: InChI=1S/C10H8/c1-2-5-9-7-4-8-10(9)6-3-1/h1-8H
Key: CUFNKYGDVFVPHO-UHFFFAOYSA-N
InChI=1/C10H8/c1-2-5-9-7-4-8-10(9)6-3-1/h1-8H
Key: CUFNKYGDVFVPHO-UHFFFAOYAT
SMILES: c1cccc2cccc2c1

Empirical Formula (Hill Notation): C10H8
CAS Number: 275-51-4
Molecular Weight: 128.17
UNSPSC Code: 12352100
NACRES: NA.22
PubChem Substance ID: 24891490
EC Number: 205-993-6
Beilstein/REAXYS Number: 969517
MDL number: MFCD00003810
Assay: 99%
Form: crystals

Properties of Azulene:
Chemical formula: C10H8
Molar mass: 128.174 g·mol−1
Appearance: Dark blue crystalline solid
Melting point: 99 to 100 °C (210 to 212 °F; 372 to 373 K)
Boiling point: 242 °C (468 °F; 515 K)
Magnetic susceptibility (χ): −98.5·10−6 cm3/mol

Molecular Weight: 128.17 g/mol
XLogP3: 3.2
Hydrogen Bond Donor Count: 0
Hydrogen Bond Acceptor Count: 0
Rotatable Bond Count: 0
Exact Mass: 128.062600255 Da
Monoisotopic Mass: 128.062600255 Da
Topological Polar Surface Area: 0 Ų
Heavy Atom Count: 10
Complexity: 94.6
Isotope Atom Count: 0
Defined Atom Stereocenter Count: 0
Undefined Atom Stereocenter Count: 0
Defined Bond Stereocenter Count: 0
Undefined Bond Stereocenter Count: 0
Covalently-Bonded Unit Count: 1
Compound Is Canonicalized: Yes

Quality Segment: 200
assay: 99%
form: crystals
bp: 242 °C (lit.)
mp: 98-100 °C (lit.)
SMILES string: c1ccc2cccc2cc1
InChI: 1S/C10H8/c1-2-5-9-7-4-8-10(9)6-3-1/h1-8H
InChI key: CUFNKYGDVFVPHO-UHFFFAOYSA-N

Thermochemistry of Azulene:
Std enthalpy of combustion (ΔcH⦵298): −1266.5 kcal/mol

Related compounds of Azulene:
Naphthalene
Bicyclo(6.2.0)decapentaene
Pentalene
Heptalene
Sesquifulvalene

Names of Azulene:

Preferred IUPAC name:
Azulene

Systematic IUPAC name:
Bicyclo[5.3.0]deca-2,4,6,8,10-pentaene