Pyrene
Encyclopedia
Pyrene is a polycyclic aromatic hydrocarbon
(PAH) consisting of four fused benzene
rings, resulting in a flat aromatic
system. The chemical formula is . This colourless solid is the smallest peri-fused PAH (one where the rings are fused through more than one face). Pyrene forms during incomplete combustion of organic compounds.
, where it occurs up to 2% by weight. As a peri-fused PAH, pyrene is much more resonance-stabilized
than its five-member-ring containing isomer fluoranthene
. Therefore, it is produced in a wide range of combustion conditions. For example, automobiles produce about 1 μg/km.
Oxidation with chromate
affords perinaphthenone and then naphthalene-1,4,5,8-tetracarboxylic acid. It undergoes a series of hydrogenation
reactions, and it is susceptible to halogenation, Diels-Alder additions, and nitration, all with varying degrees of selectivity.
s and dye precursors, for example pyranine
and naphthalene-1,4,5,8-tetracarboxylic acid. Its derivatives are also valuable molecular probes via fluorescence
spectroscopy, having a high quantum yield and lifetime (0.65 and 410 nanoseconds, respectively, in ethanol
at 293 K). Its fluorescence emission spectrum
is very sensitive to solvent polarity, so pyrene has been used as a probe to determine solvent environments. This is due to its excited state having a different, non-planar structure than the ground state. Certain emission bands are unaffected, but others vary in intensity due to the strength of interaction with a solvent.
, animal studies
have shown pyrene is toxic to the kidneys and the liver
.
Polycyclic aromatic hydrocarbon
Polycyclic aromatic hydrocarbons , also known as poly-aromatic hydrocarbons or polynuclear aromatic hydrocarbons, are potent atmospheric pollutants that consist of fused aromatic rings and do not contain heteroatoms or carry substituents. Naphthalene is the simplest example of a PAH...
(PAH) consisting of four fused 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....
rings, resulting in a flat aromatic
Aromaticity
In organic chemistry, Aromaticity is a chemical property in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibit a stabilization stronger than would be expected by the stabilization of conjugation alone. The earliest use of the term was in an article by August...
system. The chemical formula is . This colourless solid is the smallest peri-fused PAH (one where the rings are fused through more than one face). Pyrene forms during incomplete combustion of organic compounds.
Occurrence and reactivity
Pyrene was first isolated from coal tarCoal tar
Coal tar is a brown or black liquid of extremely high viscosity, which smells of naphthalene and aromatic hydrocarbons. Coal tar is among the by-products when coal iscarbonized to make coke or gasified to make coal gas...
, where it occurs up to 2% by weight. As a peri-fused PAH, pyrene is much more resonance-stabilized
Resonance (chemistry)
In chemistry, resonance or mesomerism is a way of describing delocalized electrons within certain molecules or polyatomic ions where the bonding cannot be expressed by one single Lewis formula...
than its five-member-ring containing isomer fluoranthene
Fluoranthene
Fluoranthene is a polycyclic aromatic hydrocarbon consisting of a naphthalene and a benzene unit connected by a five-membered ring. It is a member of the class of PAHs known as non-alternant PAHs because it has rings other than those with six carbon atoms. It is a structural isomer of the...
. Therefore, it is produced in a wide range of combustion conditions. For example, automobiles produce about 1 μg/km.
Oxidation with chromate
Chromate
Chromate salts contain the chromate anion, CrO42−. Dichromate salts contain the dichromate anion, Cr2O72−. They are oxyanions of chromium in the oxidation state +6. They are moderately strong oxidizing agents.- Chemical properties :...
affords perinaphthenone and then naphthalene-1,4,5,8-tetracarboxylic acid. It undergoes a series of hydrogenation
Hydrogenation
Hydrogenation, to treat with hydrogen, also a form of chemical reduction, is a chemical reaction between molecular hydrogen and another compound or element, usually in the presence of a catalyst. The process is commonly employed to reduce or saturate organic compounds. Hydrogenation typically...
reactions, and it is susceptible to halogenation, Diels-Alder additions, and nitration, all with varying degrees of selectivity.
Applications
Pyrene and its derivatives are used commercially to make dyeDye
A dye is a colored substance that has an affinity to the substrate to which it is being applied. The dye is generally applied in an aqueous solution, and requires a mordant to improve the fastness of the dye on the fiber....
s and dye precursors, for example pyranine
Pyranine
Pyranine is a hydrophilic, pH-sensitive fluorescent dye from the group of chemicals known as arylsulfonates. Pyranine is soluble in water and has applications as a coloring agent, biological stain, optical detecting reagent, and a pH indicator. One example would be the measurement of intracellular pH...
and naphthalene-1,4,5,8-tetracarboxylic acid. Its derivatives are also valuable molecular probes via fluorescence
Fluorescence
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation of a different wavelength. It is a form of luminescence. In most cases, emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation...
spectroscopy, having a high quantum yield and lifetime (0.65 and 410 nanoseconds, respectively, in ethanol
Ethanol
Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...
at 293 K). Its fluorescence emission spectrum
Emission spectrum
The emission spectrum of a chemical element or chemical compound is the spectrum of frequencies of electromagnetic radiation emitted by the element's atoms or the compound's molecules when they are returned to a lower energy state....
is very sensitive to solvent polarity, so pyrene has been used as a probe to determine solvent environments. This is due to its excited state having a different, non-planar structure than the ground state. Certain emission bands are unaffected, but others vary in intensity due to the strength of interaction with a solvent.
Safety
Although it is not as problematic as benzopyreneBenzopyrene
Benzo[a]pyrene, C20H12, is a five-ring polycyclic aromatic hydrocarbon whose metabolites are mutagenic and highly carcinogenic. Benzo[a]pyrene is listed as a Group 1 carcinogen by the IARC. It belongs to a class of polycyclic aromatic compounds known as benzopyrenes, which consist of a benzene...
, animal studies
Animal studies
Animal studies is a recently recognized field in which animals are studied in a variety of cross-disciplinary ways. Scholars from fields as diverse as: art history, anthropology, biology, film studies, geography, history, psychology, literary studies, museology, philosophy, and sociology; and from...
have shown pyrene is toxic to the kidneys and the liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
.