Carbazole
Encyclopedia
Carbazole is an aromatic heterocyclic
organic compound
. It has a tricyclic structure, consisting of two six-membered benzene
ring 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 4a–9a double bond in carbazole).
for carbazole is the Borsche–Drechsel cyclization.
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
. In the third step this compound is oxidized by Red lead
to carbazole itself. Another classic is the Bucherer carbazole synthesis
A second 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 set free and the carbazole is formed.
Heterocyclic compound
A heterocyclic compound is a cyclic compound which has atoms of at least two different elements as members of its ring. The counterparts of heterocyclic compounds are homocyclic compounds, the rings of which are made of a single element....
organic compound
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...
. It has a tricyclic structure, consisting of two six-membered benzene
Benzene
Benzene is an organic chemical compound. It is composed of 6 carbon atoms in a ring, with 1 hydrogen atom attached to each carbon atom, with the molecular formula C6H6....
ring fused on either side of a five-membered nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
-containing ring. The compound's structure is based on the indole
Indole
Indole is an aromatic heterocyclic organic compound. It has a bicyclic structure, consisting of a six-membered benzene ring fused to a five-membered nitrogen-containing pyrrole ring. Indole is a popular component of fragrances and the precursor to many pharmaceuticals. Compounds that contain an...
structure but in which a second benzene
Benzene
Benzene is an organic chemical compound. It is composed of 6 carbon atoms in a ring, with 1 hydrogen atom attached to each carbon atom, with the molecular formula C6H6....
ring is fused onto the five-membered ring at the 2–3 position of indole (equivalent to the 4a–9a double bond in carbazole).
Synthesis
A classic laboratory organic synthesisOrganic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...
for carbazole is the Borsche–Drechsel cyclization.
In the first step phenylhydrazine
Phenylhydrazine
Phenylhydrazine is the chemical compound with the formula C6H5NHNH2. Organic chemists abbreviate the compound as PhNHNH2.- Chemical properties :...
is condensed
Condensation reaction
A condensation reaction is a chemical reaction in which two molecules or moieties combine to form one single molecule, together with the loss of a small molecule. When this small molecule is water, it is known as a dehydration reaction; other possible small molecules lost are hydrogen chloride,...
with cyclohexanone
Cyclohexanone
Cyclohexanone is the organic compound with the formula 5CO. The molecule consists of six-carbon cyclic molecule with a ketone functional group. This colorless oil has an odor reminiscent of peardrop sweets as well as acetone. Over time, samples assume a yellow color due to oxidation...
to the corresponding imine
Imine
An imine is a functional group or chemical compound containing a carbon–nitrogen double bond, with the nitrogen attached to a hydrogen atom or an organic group. If this group is not a hydrogen atom, then the compound is known as a Schiff base...
. The second step is a hydrochloric acid
Hydrochloric acid
Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....
catalyzed rearrangement reaction
Rearrangement reaction
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 atom in the same molecule...
and ring-closing reaction to tetrahydrocarbazole. In one modification both steps are rolled into one by carrying out the reaction in acetic acid
Acetic acid
Acetic acid is an organic compound with the chemical formula CH3CO2H . It is a colourless liquid that when undiluted is also called glacial acetic acid. Acetic acid is the main component of vinegar , and has a distinctive sour taste and pungent smell...
. In the third step this compound is oxidized by Red lead
Red lead
Lead tetroxide, also called minium, red lead or triplumbic tetroxide, is a bright red or orange crystalline or amorphous pigment. Chemically, red lead is lead tetroxide, Pb3O4, or 2PbO·PbO2....
to carbazole itself. Another classic is the Bucherer carbazole synthesis
Bucherer carbazole synthesis
The Bucherer carbazole synthesis is a chemical reaction used to synthesize carbazoles from naphthols and aryl hydrazines using sodium bisulfite. The reaction is named after Hans Theodor Bucherer.-References:...
A second 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
O-Phenylenediamine
o-Phenylenediamine is a organic compound with the formula C6H42. This aromatic diamine is an important precursor to many heterocyclic compounds...
) is converted into a diazonium salt which instantaneously forms a 1,2,3-triazole
1,2,3-Triazole
1,2,3-Triazole is one of a pair of isomeric chemical compounds with molecular formula C2H3N3, called triazoles, which have a five-membered ring of two carbon atoms and three nitrogen atoms...
. The triazole is unstable and at elevated temperatures nitrogen is set free and the carbazole is formed.
Supply and demand
2010 and 2011 have seen wide spread shortages of Carbazole.Related aromatic compounds
- IndolineIndolineIndoline is an aromatic heterocyclic organic compound. It has a bicyclic structure, consisting of a six-membered benzene ring fused to a five-membered nitrogen-containing ring. The compound is based on the indole structure, but the 2-3 bond is saturated. by oxidation/dehydrogenation it can be...
- IndoleIndoleIndole is an aromatic heterocyclic organic compound. It has a bicyclic structure, consisting of a six-membered benzene ring fused to a five-membered nitrogen-containing pyrrole ring. Indole is a popular component of fragrances and the precursor to many pharmaceuticals. Compounds that contain an...
- Carboline
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- PyrrolePyrrolePyrrole is a heterocyclic aromatic organic compound, a five-membered ring with the formula C4H4NH. It is a colourless volatile liquid that darkens readily upon exposure to air. Substituted derivatives are also called pyrroles, e.g., N-methylpyrrole, C4H4NCH3...
- N-VinylcarbazoleN-VinylcarbazoleN-Vinylcarbazole is an organic compound used as a monomer in the production of poly, a photoconductive polymer used in the photoreceptors of photocopiers. Upon exposure to γ-irradiation, N-vinylcarbazole undergoes solid-state polymerisation....