Pyrene
Chemical compound
Pyrene is a polycyclic aromatic hydrocarbon (PAH) with the formula C16H10. Consisting of four fused benzene rings, it in a flat aromatic compound. This colorless compound 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.
01Occurrence and properties
Pyrene was first isolated from coal tar, 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.
Reactions
Pyrene contains two kinds of ring subunits: two a-rings with three CH bonds and two b-rings with two CH bonds. The a-rings are more susceptible to reactions with electrophiles and oxidants. The b-rings can be partially hydrogenated to give tetrahydropyrene. Similarly the b-rings can be oxygenated to give the quinone-like derivative C16H8O2
Oxidation with chromate affords perinaphthenone and then naphthalene-1,4,5,8-tetracarboxylic acid. Pyrene undergoes a series of hydrogenation reactions and is susceptible to halogenation, Diels-Alder additions, and nitration, all with varying degrees of selectivity. Bromination occurs at one of the 1-positions.
Reduction with sodium affords the radical anion. From this anion, a variety of pi-arene complexes can be prepared.
Pyrene and its derivatives are used commercially to make dyes and dye precursors, for example pyranine and naphthalene-1,4,5,8-tetracarboxylic acid.
02Photophysics
Pyrene has been described as "one of the most studied organic molecules in terms of its photophysical properties ..., by far, the most frequently applied dye in fluorescence labeled polymers". It is an electron donor in some donor-acceptor systems. Its potential as a photocatalyst has also been heavily investigated.
Pyrene was the first molecule for which excimer behavior was discovered. Such excimer appears around 450 nm. Theodor Förster reported this in 1954.
Pyrene's fluorescence emission spectrum is very sensitive to solvent polarity.
03Safety and environmental factors
Although it is not as problematic as benzopyrene, animal studies have shown pyrene is toxic to the kidneys and liver. It is now known that pyrene affects several living functions in fish and algae.
Its biodegradation has been heavily examined. The process commences with dihydroxylation at each of two kinds of CH=CH linkages. Experiments in pigs show that urinary 1-hydroxypyrene is a metabolite of pyrene, when given orally.
04Cited sources
- Haynes, William M., ed. (2016). CRC Handbook of Chemistry and Physics (97th ed.). CRC Press. ISBN 978-1-4987-5429-3.
Sources and credits
This article is adapted from the Wikipedia article “Pyrene”, written by its contributors and licensed under CC BY-SA 4.0. Fathomly has changed the layout, removed citation markers, navigation and maintenance notices, and adjusted punctuation. This adapted version is shared under the same license. For references, see the original article.
Images, from Wikimedia Commons:
- Pyrene.svg by Inductiveload, Public domain
- Pyrene-numbering.svg by Hbf878, CC0
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