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Chemical compound From Wikipedia, the free encyclopedia
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).
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| Names | |
|---|---|
| Preferred IUPAC name
9H-Carbazole[1] | |
| Other names
9-azafluorene dibenzopyrrole diphenylenimine diphenyleneimide USAF EK-600 | |
| Identifiers | |
3D model (JSmol) |
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| 3956 | |
| ChEBI | |
| ChEMBL | |
| ChemSpider | |
| DrugBank | |
| ECHA InfoCard | 100.001.542 |
| EC Number |
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| 102490 | |
| KEGG | |
PubChem CID |
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| RTECS number |
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| UNII | |
CompTox Dashboard (EPA) |
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| 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)[2] |
| Boiling point | 354.69 °C (670.44 °F; 627.84 K)[2] |
| −117.4 × 10−6 cm3 mol−1 | |
| Hazards | |
| GHS labelling: | |
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| Warning | |
| H341, H351, H400, H411, H413 | |
| P201, P202, P273, P281, P308+P313, P391, P405, P501 | |
| Flash point | 220 °C (428 °F; 493 K)[2] |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Carbazole is a constituent of tobacco smoke.[3]
Carl Graebe and Carl Glaser first isolated the compound from coal tar in 1872.[4]
Few carbazole production methods are economically viable, due to limited demand. During coal tar distillation, carbazole concentrates in the anthracene distillate and must be removed before anthraquinone production; that waste product is the major industrial carbazole source.[4][5] Polar compounds (e.g., ketones) selectively precipitate it from the anthracene; a more modern technique is simply selective crystallization from molten coal tar at high temperature[4] or low pressure (70 mmHg).[6]
A classic laboratory organic synthesis for carbazole is the Borsche–Drechsel cyclization.[7][8]
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.[9] 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.[10]
A third method for the synthesis of carbazole is the 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 released and the carbazole is formed.[11][12]
Diphenylamine derivatives, being electron rich, naturally oxidize to carbazoles when heated in air.[13] A similar reaction is the Mallory reaction:
Substituted carbazoles are most easily synthesized with transition metal coupling reactions. For applications that transition-metal impurities in the final product might inhibit, an alternative is nucleophilic aromatic substitution on dibenzothiophene dioxide.[14]
Carbazoles occur naturally in carbazole alkaloids. Carbazole alkaloids with unsubstituted benzene rings occur rarely. Olivacin has been found in the bark of Aspidosperma olivaceum and ellipticin in Ochrosia elliptica.[15] Some carbazole alkaloids, especially glybomin B, have been isolated from Glycosmis pentaphylla.[16]
As carbazoles have a relatively rich UV-visible light spectrum, they see application as pigments[4] and photocatalysts.[17] The parent carbazole is used in Hydron Blue production[4] and aminoethylcarbazole is used in pigment violet 23 production.[18]
Carbazoles stabilize triplet emitters in certain light-emitting diodes;[4] in general, they are electron photodonors (hole acceptors).[19]
Carbazole electrochemically oxidizes to a conductive polymer, which has not achieved substantial industrial use.[20] Polyvinylcarbazole is useful in the electrical and electronic industries, and certain carbazole novolaks are extremely heat resistant.[4]
In organic chemistry, carbazole proper is also an ingredient for several bioactive molecules. The insecticide Nirosan,[4] the cocaine overdose antidote Rimcazole, and the veterinary NSAID Carprofen are all made from carbazole. The topoisomerase II inhibitor ellipticine fuses carbazole to a pyridine ring.
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