Carbazole is an

aromatic In organic chemistry, aromaticity is a chemical property describing the way in which a conjugated system, conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibits a stabilization stronger than would be expected from conjugati ...

heterocyclic A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different elements as members of its ring(s). Heterocyclic organic chemistry is the branch of organic chemistry dealing with the synthesis, proper ...

organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...

. It has a tricyclic structure, consisting of two six-membered

benzene Benzene is an Organic compound, organic chemical compound with the Chemical formula#Molecular formula, molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar hexagonal Ring (chemistry), ring with one hyd ...

rings fused on either side of a five-membered

nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...

-containing ring. The compound's structure is based on the

indole Indole is an organic compound with the formula . Indole is classified as an aromatic heterocycle. It has a bicyclic structure, consisting of a six-membered benzene ring fused to a five-membered pyrrole ring. Indoles are derivatives of indole ...

structure, but in which a second

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 is a constituent of

tobacco smoke Tobacco smoke is a sooty aerosol produced by the incomplete combustion of tobacco during the smoking of cigarettes and other tobacco products. Temperatures in burning cigarettes range from about 400 °C between puffs to about 900 °C ...

History

Carl Graebe Carl Graebe (; 24 February 1841 – 19 January 1927) was a German industrial and academic chemist from Frankfurt am Main who held professorships in his field at Leipzig, Königsberg, and Geneva. He is known for the first synthesis of the econom ...

and Carl Glaser first isolated the compound from

coal tar Coal tar is a thick dark liquid which is a by-product of the production of coke and coal gas from coal. It is a type of creosote. It has both medical and industrial uses. Medicinally it is a topical medication applied to skin to treat psoria ...

in 1872.

Production

Few carbazole production methods are economically viable, due to limited demand. During coal tar distillation, carbazole concentrates in the

anthracene Anthracene is a solid polycyclic aromatic hydrocarbon (PAH) of formula C14H10, consisting of three fused benzene rings. It is a component of coal tar. Anthracene is used in the production of the red dye alizarin and other dyes, as a scintil ...

distillate and must be removed before

anthraquinone Anthraquinone, also called anthracenedione or dioxoanthracene, is an aromatic hydrocarbon, aromatic organic compound with formula . Several isomers exist but these terms usually refer to 9,10-anthraquinone (IUPAC: 9,10-dioxoanthracene) wherein th ...

production; that waste product is the major industrial carbazole source. 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 or low pressure (70 mmHg). A classic laboratory

organic synthesis Organic synthesis is a branch of chemical synthesis concerned with the construction of organic compounds. Organic compounds are molecules consisting of combinations of covalently-linked hydrogen, carbon, oxygen, and nitrogen atoms. Within the gen ...

for carbazole is the

Borsche–Drechsel cyclization The Borsche–Drechsel cyclization is a chemical reaction used to synthesize tetrahydrocarbazoles by the acid-catalyzed cyclization of cyclohexanone arylhydrazones. The reaction was first described by in 1888 and by in 1908. Borsche–Drechsel ...

In the first step,

phenylhydrazine Phenylhydrazine is the chemical compound with the formula . It is often abbreviated as . It is also found in edible mushrooms. Properties Phenylhydrazine forms monoclinic prisms that melt to an oil around room temperature which may turn yellow ...

is condensed with

cyclohexanone Cyclohexanone is the organic compound with the formula (CH2)5CO. The molecule consists of six-carbon cyclic molecule with a ketone functional group. This colorless oily liquid has a sweet odor reminiscent of benzaldehyde. Over time, samples of ...

to the corresponding

imine In organic chemistry, an imine ( or ) is a functional group or organic compound containing a carbon–nitrogen double bond (). The nitrogen atom can be attached to a hydrogen or an organic group (R). The carbon atom has two additional single bon ...

. The second step is a

hydrochloric acid Hydrochloric acid, also known as muriatic acid or spirits of salt, is an aqueous solution of hydrogen chloride (HCl). It is a colorless solution with a distinctive pungency, pungent smell. It is classified as a acid strength, strong acid. It is ...

-catalyzed

rearrangement reaction In organic chemistry, a rearrangement reaction is a broad class of organic reactions where the carbon skeleton of a molecule is rearranged to give a structural isomer of the original molecule. Often a substituent moves from one atom to another at ...

and

ring-closing reaction A cyclic compound (or ring compound) is a term for a compound in the field of chemistry in which one or more series of atoms in the compound is connected to form a ring. Rings may vary in size from three to many atoms, and include examples where ...

tetrahydrocarbazole Tetrahydrocarbazole is a heterocyclic compound featuring a fused structure composed of a five-membered pyrrole ring, a benzene ring, and a cyclohexane ring, making it a partially saturated derivative of carbazole. This molecular framework is common ...

. In one modification, both steps are rolled into one by carrying out the reaction in

acetic acid Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main compone ...

. In the third step, this compound is oxidized by

red lead Red is the color at the long wavelength end of the visible spectrum of light, next to orange and opposite violet. It has a dominant wavelength of approximately 625–750 nanometres. It is a primary color in the RGB color model and a secondar ...

to carbazole itself. Another classic is the

Bucherer carbazole synthesis The Bucherer carbazole synthesis is a chemical reaction used to synthesize carbazoles from 2-naphthols and aryl hydrazines using sodium bisulfite. The reaction is named after Hans Theodor Bucherer. See also * Borsche-Drechsel cyclization *Buch ...

, which uses a naphthol and an aryl hydrazine. Bucherer-Carbazol-Synthese V8

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 Diazonium compounds or diazonium salts are a group of organic compounds sharing a common functional group where R can be any organic group, such as an alkyl or an aryl, and X is an inorganic or organic anion, such as a halide. The parent, compou ...

salt In common usage, salt is a mineral composed primarily of sodium chloride (NaCl). When used in food, especially in granulated form, it is more formally called table salt. In the form of a natural crystalline mineral, salt is also known as r ...

which instantaneously forms a

1,2,3-triazole 1,2,3-Triazole is one of a pair of isomeric chemical compounds with molecular formula CHN, called triazoles, which have a five-membered ring of two carbon atoms and three nitrogen atoms. 1,2,3-Triazole is a basic aromatic heterocycle. Synthesis ...

. The triazole is unstable and at elevated temperatures, nitrogen is released and the carbazole is formed. DClPhCz kristall

Diphenylamine Diphenylamine is an organic compound with the formula (C6H5)2NH. The compound is a derivative of aniline, consisting of an amine bound to two phenyl groups. The compound is a colorless solid, but commercial samples are often yellow due to oxidiz ...

derivatives, being

electron rich Electron-rich is jargon that is used in multiple related meanings with either or both kinetic and thermodynamic implications: * with regards to electron-transfer, electron-rich species have low ionization energy and/or are reducing agents. Tetrak ...

, naturally oxidize to carbazoles when heated in air. A similar reaction is the

Mallory reaction In organic chemistry, the Mallory reaction is a Organic photochemistry, photochemical-cyclization–Elimination reaction, elimination reaction of diaryl-ethylene structures to form phenanthrenes and other polycyclic form polycyclic aromatic hydroca ...

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 A nucleophilic aromatic substitution (SNAr) is a substitution reaction in organic chemistry in which the nucleophile displaces a good leaving group, such as a halide, on an aromatic ring. Aromatic rings are usually nucleophilic, but some aromatic c ...

dibenzothiophene Dibenzothiophene (DBT, diphenylene sulfide) is the organosulfur compound consisting of two benzene rings fused to a central thiophene ring. It has the chemical formula C12H8S. It is a colourless solid that is chemically somewhat similar to anth ...

dioxide.

Natural Occurrence

Carbazoles occur naturally in carbazole alkaloids. Carbazole alkaloids with unsubstituted

rings occur rarely. Olivacin has been found in the bark of '' Aspidosperma olivaceum'' and ellipticin in ''

Ochrosia elliptica ''Ochrosia elliptica'', commonly known as northern ochrosia, bloodhorn, scarlet wedge-apple, or simply ochrosia, is a tree in the dogbane family Apocynaceae native to north-eastern Australia and the southwest Pacific. Description The northern ...

''. Some carbazole alkaloids, especially glybomin B, have been isolated from ''

Glycosmis pentaphylla ''Glycosmis pentaphylla'' is a species of flowering plant in the family Rutaceae, known commonly as orangeberry and gin berry. It occurs in Southeast Asia and northern Australia. It is cultivated for its edible pink fruits. In temperate zones, it ...

''.

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

Applications

As carbazoles have a relatively rich UV-visible light spectrum, they see application as pigments and

photocatalyst In chemistry, photocatalysis is the acceleration of a photoreaction in the presence of a photocatalyst, the excited state of which "repeatedly interacts with the reaction partners forming reaction intermediates and regenerates itself after each ...

s. The parent carbazole is used in Hydron Blue production and aminoethylcarbazole is used in

pigment violet 23 Pigment violet 23 is an organic compound that is a commercial pigment. It is member of the dioxazine family of heterocyclic compounds, but derived from carbazoles. It is prepared by condensation of chloranil and 3-amino-''N''-ethylcarbazole. It ...

production. CI Pigment Violet 23 Synthesis

Carbazoles stabilize triplet emitters in certain

light-emitting diodes A light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light (corresp ...

; in general, they are electron photodonors (hole acceptors). Carbazole electrochemically oxidizes to a

conductive polymer Conductive polymers or, more precisely, intrinsically conducting polymers (ICPs) are organic polymers that conduct electricity. Such compounds may have metallic conductivity or can be semiconductors. The main advantage of conductive polymers ...

, which has not achieved substantial industrial use.

Polyvinylcarbazole Polyvinylcarbazole (PVK) is a temperature-resistantHans-Dieter Jakubke, Ruth Karcher (Koordinatoren): ''Lexikon der Chemie'' in drei Bänden, Spektrum Verlag, Band 3, Heidelberg 1999, , S. 92. thermoplastic polymer produced by radical polymerizat ...

is useful in the electrical and electronic industries, and certain carbazole

novolak Novolaks (sometimes: novolacs) are low molecular weight polymers derived from phenols and formaldehyde. They are related to Bakelite, which is more highly crosslinked. The term comes from Swedish "lack" for lacquer and Latin "novo" for new, sinc ...

s are extremely heat resistant. In organic chemistry, carbazole proper is also an ingredient for several bioactive molecules. The insecticide Nirosan, the

cocaine overdose Cocaine intoxication refers to the subjective, desired and adverse effects of cocaine on the mind and behavior of users. Both self-induced and involuntary cocaine intoxication have medical and legal implications (even in absence of relevant advers ...

antidote

Rimcazole Rimcazole is an antagonist of the sigma receptor as well as a dopamine reuptake inhibitor. Sigma receptors are thought to be involved in the drug psychosis that can be induced by some drugs such as phencyclidine and cocaine, and rimcazole was or ...

, and the

veterinary Veterinary medicine is the branch of medicine that deals with the prevention, management, diagnosis, and treatment of disease, disorder, and injury in non-human animals. The scope of veterinary medicine is wide, covering all animal species, both ...

NSAID

Carprofen Carprofen is a nonsteroidal anti-inflammatory drug (NSAID) of the carbazole and propionic acid class that was previously for use in humans and animals but is now only available to veterinarians for prescribing as a supportive treatment for va ...

are all made from carbazole. The

topoisomerase II Type II topoisomerases are topoisomerases that cut both strands of the DNA helix simultaneously in order to manage DNA tangles and supercoils. They use the hydrolysis of Adenosine triphosphate, ATP, unlike Type I topoisomerase. In this process, t ...

inhibitor

ellipticine Ellipticine is a tetracyclic alkaloid first extracted from the tree species ''Ochrosia elliptica'' and ''Rauvolfia sandwicensis'' which inhibits the enzyme topoisomerase II via intercalation (biochemistry), intercalative binding to DNA. ...

fuses carbazole to a

pyridine Pyridine is a basic (chemistry), basic heterocyclic compound, heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom . It is a highly flammable, weak ...

ring.

References

External links

MSDS

Color change upon deprotonation
{{Authority control IARC Group 2B carcinogens