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==History==
[[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
A classic laboratory [[organic synthesis]] for carbazole is the [[Borsche–Drechsel cyclization]].<ref>{{cite journal
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[[File:Borsche-Drechsel cyclization.svg|center|300px|Borsche–Drechsel synthesis]]
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>
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[[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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[[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|upright=2.5|Pigment Violet 23 synthesis]]
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]]
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