Carbazole

Carbazole is an aromatic heterocyclic organic compound. It has a tricyclic structure, consisting of two six-membered benzene rings fused on either side of a five-membered nitrogen-containing ring. The compound's structure is based on the indole structure, but in which a second benzene ring is fused onto the five-membered ring at the 2–3 position of indole (equivalent to the 9a–4a double bond in carbazole, respectively).

Carbazole
Names
IUPAC name
9H-carbazole
Other names
9-azafluorene
dibenzopyrrole
diphenylenimine
diphenyleneimide
USAF EK-600
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
DrugBank
ECHA InfoCard 100.001.542
KEGG
UNII
Properties
C12H9N
Molar mass 167.211 g·mol−1
Density 1.301 g cm−3
Melting point 246.3 °C (475.3 °F; 519.5 K)[1]
Boiling point 354.69 °C (670.44 °F; 627.84 K)[1]
−117.4 × 10−6 cm3 mol−1
Hazards
Flash point 220 °C (428 °F; 493 K) [1]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Carbazole is a constituent of tobacco smoke.[2]

Synthesis

A classic laboratory organic synthesis for carbazole is the Borsche–Drechsel cyclization.[3][4]

Borsche–Drechsel synthesis

In the first step, phenylhydrazine is condensed with cyclohexanone to the corresponding imine. The second step is a hydrochloric acid-catalyzed rearrangement reaction and ring-closing reaction to tetrahydrocarbazole. In one modification, both steps are rolled into one by carrying out the reaction in acetic acid.[5] In the third step, this compound is oxidized by red lead to carbazole itself.

Another classic is the Bucherer carbazole synthesis, which uses a naphthol and an aryl hydrazine.[6]

Bucherer carbazole synthesis

A third method for the synthesis of carbazole is the Graebe–Ullmann reaction.

Graebe–Ullmann reaction

In the first step, an N-phenyl-1,2-diaminobenzene (N-phenyl-o-phenylenediamine) is converted into a diazonium salt which instantaneously forms a 1,2,3-triazole. The triazole is unstable and at elevated temperatures, nitrogen is set free and the carbazole is formed.[7][8]

Applications

Aminoethylcarbazole is used in the production of pigment violet 23.

CI Pigment Violet 23 synthesis: U.S. Patent 4,345,074
  • Rimcazole is also made from carbazole proper.
  • Carprofen is another use.
  • NNC 05-2090 & NNC 05-2045 are both uncommon, but still technical case examples.

References
  1. Lide, David R. (2007). CRC Handbook of Chemistry and Physics, 88th Edition. CRC Press. pp. 3–86. ISBN 978-0-8493-0488-0.
  2. Talhout, Reinskje; Schulz, Thomas; Florek, Ewa; Van Benthem, Jan; Wester, Piet; Opperhuizen, Antoon (2011). "Hazardous Compounds in Tobacco Smoke". Int. J. Environ. Res. Public Health. 8 (12): 613–628. doi:10.3390/ijerph8020613. PMC 3084482. PMID 21556207.
  3. W. Borsche (1908). "Ueber Tetra- und Hexahydrocarbazolverbindungen und eine neue Carbazolsynthese. (Mitbearbeitet von. A. Witte und W. Bothe.)". Justus Liebigs Ann. Chem. (in German). 359 (1–2): 49–80. doi:10.1002/jlac.19083590103.
  4. E. Drechsel (1888). "Ueber Elektrolyse des Phenols mit Wechselströmen". J. Prakt. Chem. (in German). 38 (1): 65–74. doi:10.1002/prac.18880380105.
  5. Rogers, Crosby U.; Corson, B. B. (1950). "1,2,3,4-Tetrahydrocarbazole (Carbazole, 1,2,3,4-tetrahydro-)". Organic Syntheses. 30: 90. doi:10.15227/orgsyn.030.0090.; Collective Volume, 4, p. 884
  6. Wang, Zerong (2010). "Bucherer Carbazole Synthesis". Comprehensive Organic Name Reactions and Reagents. doi:10.1002/9780470638859.conrr120.
  7. Carl Graebe; Fritz Ullmann (1896). "Ueber eine neue Carbazolsynthese". Justus Liebigs Ann. Chem. (in German). 291 (1): 16–17. doi:10.1002/jlac.18962910104.
  8. O. Bremer (1934). "Über die Bedeutung der Graebe-Ullmannschen Carbazolsynthese und deren Übertragung auf N-substituierte Pyridino-triazole". Justus Liebigs Ann. Chem. (in German). 514 (1): 279–291. doi:10.1002/jlac.19345140116.
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