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| FlashPtC = 220
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| GHSPictograms = {{GHS08}}{{GHS09}}
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Carbazole is a constituent of [[tobacco smoke]].<ref name="TalhoutSchulz2011">{{cite journal|last1 = Talhout|first1 = Reinskje|last2 = Schulz|first2 = Thomas|last3 = Florek|first3 = Ewa|last4 = Van Benthem|first4 = Jan|last5 = Wester|first5 = Piet|last6 = Opperhuizen|first6 = Antoon|title = Hazardous Compounds in Tobacco Smoke|journal = [[Int. J. Environ. Res. Public Health]]|volume = 8|issue = 12|year = 2011|pages = 613–628|doi = 10.3390/ijerph8020613|pmid = 21556207|pmc = 3084482|doi-access = free}}</ref>
==
[[Carl Graebe]] and [[Carl Andreas Glaser|Carl Glaser]] first isolated the compound from [[coal tar]] in 1872.<ref name=Ullmann>{{Ullmann|first1=Gerd|last1=Collin|first2=Hartmut|last2=Höke|first3=Jörg|last3=Talbiersky|doi=10.1002/14356007.a05_059.pub2|title=Carbazole}}</ref>
==Production==
{{Anchor|Borsche-Drechsel cyclization}}
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.<ref name=Ullmann/><ref name=KO>{{Kirk-Othmer|doi=10.1002/0471238961.0114200803150618.a01|title=Anthraquinone|p=5|first=A. J.|last=Cofrancesco}}</ref> 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<ref name=Ullmann/> or low pressure (70 mmHg).<ref>{{Kirk-Othmer|doi=10.1002/0471238961.20011802052020.a01|p=5|title=Tar and Pitch|first=W. D.|last=Betts}}</ref>
A classic laboratory [[organic synthesis]] for carbazole is the [[Borsche–Drechsel cyclization]].<ref>{{cite journal
| title = Ueber Tetra- und Hexahydrocarbazolverbindungen und eine neue Carbazolsynthese. (Mitbearbeitet von. A. Witte und W. Bothe.)
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}}</ref>
[[File:
In the first step, [[phenylhydrazine]] is [[condensation reaction|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]].<ref>{{OrgSynth|collvol = 4|collvolpages = 884|volume = 30|pages = 90|year = 1950|prep = CV4P0884|doi = 10.15227/orgsyn.030.0090|title = 1,2,3,4-Tetrahydrocarbazole (Carbazole, 1,2,3,4-tetrahydro-)|first1 = Crosby U.|last1 = Rogers|first2 = B. B.|last2 = Corson}}</ref> 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.<ref>{{cite book|first=Zerong|last=Wang|title=Comprehensive Organic Name Reactions and Reagents|chapter=Bucherer Carbazole Synthesis|year=2010|pages=549–552 |doi=10.1002/9780470638859.conrr120|isbn=9780470638859}}</ref>
[[File:Bucherer_Carbazole_Synthesis_Scheme.png|center|450px|Bucherer carbazole synthesis]]
A third method for the synthesis of carbazole is the Graebe–Ullmann reaction.
[[File:Reacción de Graebe-Ullman.png|center|450px|Graebe–Ullmann reaction]]
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| year = 1934
| doi = 10.1002/jlac.19345140116}}</ref>
[[File:DClPhCz kristall.jpg|thumb|Fluorescence of (9H-carbazol-9-yl)(2,4-dichlorophenyl) methanone]]
[[Diphenylamine]] derivatives, being [[electron rich]], [[oxidative coupling|naturally oxidize]] to carbazoles when heated in air.<ref>{{Ullmann|title=Amines, Aromatic|first1=Peter F.|last1=Vogt|first2=John J.|last2=Gerulis|doi=10.1002/14356007.a02_037|volume=2|p=703}}</ref> A similar reaction is the [[Mallory reaction]]:[[File:StilScope7.png|thumb]]
Substituted carbazoles are most easily synthesized with [[cross-coupling reaction|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.<ref>{{cite encyclopedia|title=Encyclopedia of Reagents for Organic Synthesis|doi=10.1002/047084289X.rn02046|entry=Dibenzothiophene 5,5-dioxide|first1=M.|last1=Bhanuchandra|author2=Yorimitsu Hideki}}</ref>
==Natural Occurrence==
{{Main|Carbazole alkaloids}}
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]]''.<ref name="Alkaloids2">{{citation |author=[[Eberhard Breitmaier]] |title=Alkaloide |date=1997 |pages=49 |location=Wiesbaden |publisher=Springer Fachmedien |isbn=978-3-519-03542-8}}<!-- auto-translated by Module:CS1 translator --></ref> Some carbazole alkaloids, especially glybomin B, have been isolated from ''[[Glycosmis pentaphylla]]''.<ref name="A" /><gallery widths="180">
Glycozoline Structural Formula V1.svg|Glycozoline
Olivacine Structural Formula V1.svg|Olivacine
Ellipticine Structural Formula V1.svg|Ellipticin
Glybomine B Structural Formula V1.svg|Glybomine B
</gallery>
==Applications==
As carbazoles have a relatively rich [[UV-vis]]ible light spectrum, they see application as pigments<ref name=Ullmann/> and [[photocatalyst]]s.<ref>{{cite encyclopedia|encyclopedia=Encyclopedia of Reagents for Organic Synthesis|doi=10.1002/047084289X.rn00578|entry=N-Methylcarbazole|first=Carmelo J.|last=Rizzo|title=''N'' -Methylcarbazole |date=2005 |isbn=0-471-93623-5 }}</ref> The parent carbazole is used in [[Hydron Blue]] production<ref name=Ullmann/> and aminoethylcarbazole is used in [[pigment violet 23]] production.<ref>{{US patent|4345074}}</ref>
[[File:CI Pigment Violet 23 Synthesis.jpg|thumb|center|
Carbazoles stabilize [[triplet state|triplet]] emitters in certain [[light-emitting diodes]];<ref name=Ullmann/> in general, they are electron photodonors (hole acceptors).<ref>{{Kirk-Othmer|title=Photoconductive polymers|doi=10.1002/0471238961.1608152023011407.a01|p=15|author=Ying Wang}}</ref>
Carbazole electrochemically oxidizes to a [[conductive polymer]], which has not achieved substantial industrial use.<ref>{{Ullmann|title=Polymers, Electrically conducting|first=Herbert|last=Naarmann|doi=10.1002/14356007.a21_429|volume=29|p=309}}</ref> [[Polyvinylcarbazole]] is useful in the electrical and electronic industries, and certain carbazole [[novolak]]s are extremely heat resistant.<ref name=Ullmann/>
In organic chemistry, carbazole proper is also an ingredient for several [[bioactive molecule]]s. The insecticide [[Nirosan]],<ref name=Ullmann/> 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.
==See also==
*[[Indole]]
*[[Carboline]]
*[[Fluorene]]
*[[Polychlorinated carbazoles]]
*[[Carbazole alkaloids]]
==References==
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{{Authority control}}
[[Category:Carbazoles| ]]
[[Category:IARC Group 2B carcinogens]]
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