All Topics  
Pyrrole

 

 
   Email Print
   Bookmark   Link
 

 

Pyrrole
 
 
  Topics Pyrrole Topic Home

Pyrrole, or pyrrol, is a heterocyclic aromatic organic compound
Organic compound

An organic compound is any member of a large class of chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of compounds such as carbonates, simple oxides of carbon and cyanides, as well as the allotropes of carbon, are considered Inorganic compound....
, a five-membered ring with the formula
Chemical formula

A chemical formula is a way of expressing information about the atoms that constitute a particular chemical compound, and how the relationship between those atoms changes in chemical reactions....
 C
Carbon

Carbon is a chemical element with chemical symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalence?making four electrons available to form covalent bond chemical bonds....
4H
Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the chemical symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly combustion and explosive Diatomic molecule gas with the molecular formula H2....
4N
Nitrogen

Nitrogen is a chemical element that has the symbol N and atomic number 7 and atomic mass 14.00674?. Elemental nitrogen is a colorless, odorless, tasteless and mostly inert diatomic gas at standard conditions, constituting 78% by volume of Earth's atmosphere....
H. Substituted derivatives are also called pyrroles. For example, C4H4NCH3 is N-methylpyrrole. Porphobilinogen
Porphobilinogen

Porphobilinogen is a pyrrole involved in porphyrin metabolism.It is generated by aminolevulinate and the enzyme ALA dehydratase. PBG is then converted into hydroxymethyl bilane by the enzyme porphobilinogen deaminase....
 is a trisubstituted pyrrole, which is the biosynthetic precursor to many natural products.

Pyrroles are components of more complex macrocycles, including the porphyrin
Porphyrin

Porphyrins are a group of chemical compounds of which many occur in nature, such as in green leaves and red blood cells, and in bio-inspired synthetic catalysts and devices....
s of heme
Heme

A heme or haem is a prosthetic group that consists of an iron atom contained in the center of a large heterocyclic organic ring called a porphyrin....
, the chlorin
Chlorin

In organic chemistry, a chlorin is a large heterocyclic aromatic ring consisting, at the core, of three pyrroles and one pyrroline coupled through four methine linkages....
s and bacteriochlorins of chlorophyll
Chlorophyll

Chlorophyll is a green pigment found in most plants, algae, and cyanobacteria. Its name is derived from Greek language: ?????? and f????? ....
, and porphyrinogens.

ole has very low basicity compared to amine
Amine

Amines are organic compounds and functional groups that contain a base nitrogen atom with a lone pair. Amines are derivative s of ammonia, wherein one or more hydrogen atoms are replaced by organic substituents such as alkyl and aryl groups....
s and other aromatic compounds like pyridine
Pyridine

Pyridine is a simple and important heterocyclic aromatic organic compound with the formula CarbonHydrogenNitrogen. This colorless liquid with a distinctive fish-like odor is structurally related to benzene, wherein one CH group in the six-membered ring is replaced by a nitrogen atom....
, wherin the ring nitrogen
Nitrogen

Nitrogen is a chemical element that has the symbol N and atomic number 7 and atomic mass 14.00674?. Elemental nitrogen is a colorless, odorless, tasteless and mostly inert diatomic gas at standard conditions, constituting 78% by volume of Earth's atmosphere....
 is not bonded to a hydrogen
Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the chemical symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly combustion and explosive Diatomic molecule gas with the molecular formula H2....
 atom
Atom

|-! bgcolor=gray | Properties|-||}The atom is a basic unit of matter consisting of a dense, central atomic nucleus surrounded by a electron cloud of electric charge electrons....
.






Discussion
Ask a question about 'Pyrrole'
Start a new discussion about 'Pyrrole'
Answer questions from other users
Full Discussion Forum



Encyclopedia


Pyrrole, or pyrrol, is a heterocyclic aromatic organic compound
Organic compound

An organic compound is any member of a large class of chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of compounds such as carbonates, simple oxides of carbon and cyanides, as well as the allotropes of carbon, are considered Inorganic compound....
, a five-membered ring with the formula
Chemical formula

A chemical formula is a way of expressing information about the atoms that constitute a particular chemical compound, and how the relationship between those atoms changes in chemical reactions....
 C
Carbon

Carbon is a chemical element with chemical symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalence?making four electrons available to form covalent bond chemical bonds....
4H
Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the chemical symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly combustion and explosive Diatomic molecule gas with the molecular formula H2....
4N
Nitrogen

Nitrogen is a chemical element that has the symbol N and atomic number 7 and atomic mass 14.00674?. Elemental nitrogen is a colorless, odorless, tasteless and mostly inert diatomic gas at standard conditions, constituting 78% by volume of Earth's atmosphere....
H. Substituted derivatives are also called pyrroles. For example, C4H4NCH3 is N-methylpyrrole. Porphobilinogen
Porphobilinogen

Porphobilinogen is a pyrrole involved in porphyrin metabolism.It is generated by aminolevulinate and the enzyme ALA dehydratase. PBG is then converted into hydroxymethyl bilane by the enzyme porphobilinogen deaminase....
 is a trisubstituted pyrrole, which is the biosynthetic precursor to many natural products.

Pyrroles are components of more complex macrocycles, including the porphyrin
Porphyrin

Porphyrins are a group of chemical compounds of which many occur in nature, such as in green leaves and red blood cells, and in bio-inspired synthetic catalysts and devices....
s of heme
Heme

A heme or haem is a prosthetic group that consists of an iron atom contained in the center of a large heterocyclic organic ring called a porphyrin....
, the chlorin
Chlorin

In organic chemistry, a chlorin is a large heterocyclic aromatic ring consisting, at the core, of three pyrroles and one pyrroline coupled through four methine linkages....
s and bacteriochlorins of chlorophyll
Chlorophyll

Chlorophyll is a green pigment found in most plants, algae, and cyanobacteria. Its name is derived from Greek language: ?????? and f????? ....
, and porphyrinogens.

Properties

Pyrrole has very low basicity compared to amine
Amine

Amines are organic compounds and functional groups that contain a base nitrogen atom with a lone pair. Amines are derivative s of ammonia, wherein one or more hydrogen atoms are replaced by organic substituents such as alkyl and aryl groups....
s and other aromatic compounds like pyridine
Pyridine

Pyridine is a simple and important heterocyclic aromatic organic compound with the formula CarbonHydrogenNitrogen. This colorless liquid with a distinctive fish-like odor is structurally related to benzene, wherein one CH group in the six-membered ring is replaced by a nitrogen atom....
, wherin the ring nitrogen
Nitrogen

Nitrogen is a chemical element that has the symbol N and atomic number 7 and atomic mass 14.00674?. Elemental nitrogen is a colorless, odorless, tasteless and mostly inert diatomic gas at standard conditions, constituting 78% by volume of Earth's atmosphere....
 is not bonded to a hydrogen
Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the chemical symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly combustion and explosive Diatomic molecule gas with the molecular formula H2....
 atom
Atom

|-! bgcolor=gray | Properties|-||}The atom is a basic unit of matter consisting of a dense, central atomic nucleus surrounded by a electron cloud of electric charge electrons....
. This decreased basicity is attributed to the delocalization of the lone pair
Lone pair

A lone pair is a valence electron pair without bonding or sharing with other atoms. They are found in the outermost electron shell of an atom, so lone pairs are a subset of a molecule's valence electrons....
 of electron
Electron

The electron is a subatomic particle that carries a negative electric charge. It has elementary particle and is believed to be a point particle....
s of the nitrogen atom in the aromatic ring. Pyrrole is a very weak base with a pKaH of about -4. Protonation results in loss of aromaticity, and is, therefore, unfavorable.

Synthesis

Many methods exist for the organic synthesis
Organic synthesis

Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic_chemistry molecules can often contain a higher level of complexity compared to purely Inorganic_chemistry compounds, so the synthesis of organic compounds has developed into one of the most im...
 of pyrrole and its derivatives. Classic named reactions are the Knorr pyrrole synthesis
Knorr pyrrole synthesis

The 'Knorr pyrrole synthesis' is a widely used chemical reaction that synthesizes substituted pyrroles . The method involves the reaction of an a-amino-ketone and a compound containing a methylene group a- to a carbonyl group ....
, the Hantzsch pyrrole synthesis
Hantzsch pyrrole synthesis

The Hantzsch pyrrole synthesis, named for Arthur Rudolf Hantzsch, is the chemical reaction of ?-ketoesters with ammonia and a-haloketones to give substituted pyrroles ....
, and the Paal-Knorr synthesis
Paal-Knorr synthesis

The Paal-Knorr synthesis is a chemical reaction where Diketone are converted to either furans, thiophenes or pyrroles. The reaction is named after Carl Paal and Ludwig Knorr...
.

The starting materials in the Piloty-Robinson pyrrole synthesis are 2 equivalents of an aldehyde
Aldehyde

An aldehyde is an organic compound containing a terminal carbonyl group. This functional group, which consists of a carbon atom bonded to a hydrogen atom and double bond to an oxygen atom , is called the aldehyde group....
 and hydrazine
Hydrazine

Hydrazine is a chemical compound with the chemical formula N2H4. It is a colourless liquid with an ammonia-like odor and is derived from the same industrial chemistry processes that manufacture ammonia....
. The product is a pyrrole with specific substituents in the 3 and 4 positions. The aldehyde reacts with the diamine to an intermediate di-imine
Imine

An imine is a functional group or chemical compound containing a carbon?nitrogen double bond . Due to their diverse reactivity, imines are common substrates in a wide variety of transformations....
 (R–C=N-N=C–R), which, with added hydrochloric acid
Hydrochloric acid

Hydrochloric acid is the solution of hydrogen chloride in water. It is a highly corrosive, strong acid mineral acid and has major industrial uses....
, gives ring-closure and loss of ammonia
Ammonia

Ammonia is a chemical compound with the chemical formula nitrogenhydrogen. It is normally encountered as a gas with a characteristic pungent odor....
 to the pyrrole.

In one modification, propionaldehyde
Propionaldehyde

Propionaldehyde or propanal is the organic compound with the formula CH3CH2CHO. It is a saturate 3-carbon aldehyde and is a structural isomerism of propanone....
 is reacted first with hydrazine
Hydrazine

Hydrazine is a chemical compound with the chemical formula N2H4. It is a colourless liquid with an ammonia-like odor and is derived from the same industrial chemistry processes that manufacture ammonia....
 and then with benzoyl chloride
Benzoyl chloride

Benzoyl chloride, also known as benzenecarbonyl chloride, is a colourless, fuming liquid, C6H5COCl, with an irritating odour....
 at high temperatures and assisted by microwave irradiation
Microwave chemistry

Microwave chemistry is the science of applying microwave irradiation to chemical reactions . Microwaves act as high frequency electric fields and will generally heat any material containing mobile electric charges, such as polar molecules in a solvent or conducting ions in a solid....
:

In the second step, a [3,3]sigmatropic reaction
Sigmatropic reaction

A Sigmatropic reaction in organic chemistry is a pericyclic reaction wherein the net result is one sigma bond changed to another sigma bond. In this type of rearrangement reaction, a substituent moves from one part of a pi-bonded system to another part in an intramolecular reaction with simultaneous rearrangement of the pi system....
 takes place between two intermediates.

One synthetic route to pyrrole involves the decarboxylation
Decarboxylation

Decarboxylation is any chemical reaction in which a carboxyl group is split off from a compound as carbon dioxide ....
 of ammonium mucate, the ammonium salt of mucic acid
Mucic acid

Mucic acid, C6H10O8 or HOOC-4-COOH, is obtained by nitric acid oxidation of galactose or galactose-containing compounds like lactose, dulcite, quercite, and most varieties of natural gum....
. The salt is typically heated in a distillation
Distillation

Distillation is a method of separation process mixtures based on differences in their Volatility in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction....
 setup with glycerol
Glycerol

Glycerol is a chemical compound also commonly called glycerin or glycerine. It is a colorless, odorless, Viscosity liquid that is widely used in pharmaceutical formulations....
 as a solvent
Solvent

A solvent is a liquid or gas that dissolves a solid, liquid, or gaseous solute, resulting in a solution.The most common solvent in everyday life is water....
.

Reactivity

Both NH and CH protons in pyrroles are moderately acidic and can be deprotonated
Deprotonation

Deprotonation is a chemistry term that refers to the removal of a proton from a molecule, forming the conjugate base. The relative ability for a molecule to give up a proton is measured by a pKa value....
 with strong base
Base (chemistry)

In chemistry, a base is most commonly thought of as an aqueous substance that can accept protons. A base is also often referred to as an alkali if OH- ions are involved....
s such as butyllithium and the metal hydrides. The resulting "pyrrolides" are nucleophilic. Trapping of the conjugate base with an electrophile
Electrophile

In chemistry, an electrophile is a reagent attracted to electrons that participates in a chemical reaction by accepting an electron pair in order to Chemical bond to a nucleophile....
 (e.g., an alkyl or acyl halide
Acyl halide

An acyl halide is a chemical compound derived from an oxoacid by replacing a hydroxyl group with a halide group.If the acid is a carboxylic acid, the compound contains a ?COX functional group, which consists of a carbonyl group singly bonded to a halogen atom....
) reveals which sites were deprotonated based on which ring positions actually react as nucleophiles. The product distribution of such a reaction can often be complex and depends on the base used (especially the counterion, such as lithium from butyllithium or sodium from sodium hydride), existing substitution of the pyrrole, and the electrophile.

The resonance contributors of pyrrole provide insight to the reactivity of the compound. Like furan
Furan

Furan, also known as furane and furfuran, is a Heterocyclic compound organic compound. It is typically derived by the thermal decomposition of pentose-containing materials, cellulosic solids especially pine-wood....
 and thiophene
Thiophene

Thiophene is the heterocyclic compound with the formula C4H4S. Consisting of a flat five-membered ring, it is aromaticity as indicated by its extensive substitution reactions....
, pyrrole is more reactive than benzene towards nucleophilic aromatic substitution
Nucleophilic aromatic substitution

A nucleophilic aromatic substitution is a substitution reaction in organic chemistry in which the nucleophile displaces a good leaving group, such as a halide on an aromatic ring....
 because it is able to stabilize the positive charge of the intermediate carbanion
Carbanion

A carbanion is an anion in which carbon has an unshared pair of electrons and bears a negative charge usually with three substituents for a total of eight valence electrons ....
. This is because the nitrogen can donate a lone pair into the ring by resonance

Pyrrole undergoes electrophilic aromatic substitution
Electrophilic aromatic substitution

Electrophilic aromatic substitution or EAS is an organic reaction in which an atom, usually hydrogen, appended to an aromatic ring is replaced by an electrophile....
 predominantly at the 2 and 5 positions, though the substitution product at positions 3 and 4 is obtained in low yields. Two such reactions that are especially significant for producing functionalized pyrroles are the Mannich reaction
Mannich reaction

The Mannich reaction is an organic reaction which consists of an amino alkylation of an acidic proton placed next to a carbonyl functional group with formaldehyde and ammonia or any primary or secondary amine....
 and the Vilsmeier-Haack reaction
Vilsmeier-Haack reaction

The Vilsmeier-Haack reaction is the chemical reaction of a substituted amide with phosphorus oxychloride and an activating group arene to produce an aryl aldehyde or ketone ....
 (depicted below) , both of which are compatible with a variety of pyrrole substrates. Reaction of pyrroles with formaldehyde
Formaldehyde

Formaldehyde is a chemical compound with the chemical formula H2CO. It is the simplest aldehyde. Formaldehyde exists in several forms aside from H2CO: the cyclic trimer trioxane and the polymer Polyoxymethylene....
 form porphyrin
Porphyrin

Porphyrins are a group of chemical compounds of which many occur in nature, such as in green leaves and red blood cells, and in bio-inspired synthetic catalysts and devices....
s.

Pyrrole compounds can also participate in cycloaddition
Cycloaddition

A cycloaddition is a pericyclic chemical reaction, in which two pi bond are lost and two sigma bond are gained. The resulting reaction is a cyclization reaction....
 (Diels-Alder) reactions under certain conditions, such as Lewis acid catalysis, heating, or high pressure.

Commercial Uses


In a 1994 report released by five top cigarette companies, pyrrole is one of the 599 additives to cigarettes.

See also

  • Arsole
    Arsole

    Arsole, rarely called arsenole, is a cyclic organoarsenic chemical compound of the chemical formula C4H5As. The structure is isoelectronic to that of pyrrole except that an arsenic atom is substituted for the nitrogen atom....
    , a moderately-aromatic arsenic
    Arsenic

    Arsenic is a well-known chemical element that has the symbol As and atomic number 33. Arsenic was first documented by Albertus Magnus in 1250....
     analog
  • Furan
    Furan

    Furan, also known as furane and furfuran, is a Heterocyclic compound organic compound. It is typically derived by the thermal decomposition of pentose-containing materials, cellulosic solids especially pine-wood....
    , an analog with an oxygen
    Oxygen

    Oxygen no O2 produced; 2) O2 produced, but absorbed in oceans & seabed rock; 3) O2 starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer; 4-5) O2 sinks filled and the gas accumulates]]...
     instead of the nitrogen
  • Indole
    Indole

    Indole is an aromatic Heterocyclic compound organic compound. It has a bicyclic structure, consisting of a six-membered benzene ring fused to a five-membered nitrogen-containing pyrrole ring....
    , a derivative with a fused benzene
    Benzene

    Benzene, or benzol, is an organic compound chemical compound and a known carcinogen with the molecular formula Carbon6Hydrogen6....
     ring
  • Phosphole
    Phosphole

    Phosphole is the organic compound with the chemical formula C4H4PH; it is the phosphorus analog of pyrrole. The term phosphole also refers to substituted derivatives of the parent heterocycle....
    , a non-aromatic phosphorus
    Phosphorus

    Phosphorus is the chemical element that has the symbol P and atomic number 15. The name comes from the and . A Valency nonmetal of the nitrogen group, phosphorus is commonly found in inorganic phosphate minerals....
     analog
  • Polypyrrole
    Polypyrrole

    A Polypyrrole is a chemical compound formed from a number of connected pyrrole ring structures. For example a tetrapyrrole is a compound with four pyrrole rings connected....
  • Pyroluria
  • Pyrroline
    Pyrroline

    Pyrrolines, also known under the name dihydropyrroles, are three different heterocyclic compound organic chemistry chemical compounds which differ in the position of the double bond....
    , a partially saturated analog with one double bond
  • Pyrrolidine
    Pyrrolidine

    Pyrrolidine, also known as tetrahydropyrrole, is an organic compound with the molecular formula C4H9N. It is a cyclic amine with a five-membered ring containing four carbon atoms and one nitrogen atom....
    , the saturated hydrogenated analog
  • Simple aromatic ring
    Simple aromatic ring

    Simple aromatic rings, also known as simple arenes or simple aromatics, are aromatic organic compounds that consist only of a conjugated system planar ring system with delocalized_electron pi electron clouds....
    s
  • Thiophene
    Thiophene

    Thiophene is the heterocyclic compound with the formula C4H4S. Consisting of a flat five-membered ring, it is aromaticity as indicated by its extensive substitution reactions....
    , an analog with a sulfur
    Sulfur

    Sulfur or sulphur is the chemical element that has the atomic number 16. It is denoted with the symbol S. It is an abundant Valence non-metal....
     instead of the nitrogen
    Nitrogen

    Nitrogen is a chemical element that has the symbol N and atomic number 7 and atomic mass 14.00674?. Elemental nitrogen is a colorless, odorless, tasteless and mostly inert diatomic gas at standard conditions, constituting 78% by volume of Earth's atmosphere....
     atom
    Atom

    |-! bgcolor=gray | Properties|-||}The atom is a basic unit of matter consisting of a dense, central atomic nucleus surrounded by a electron cloud of electric charge electrons....
    .


External links