Dicoronylene is the

trivial name In chemistry, a trivial name is a non systematic name for a chemical substance. That is, the name is not recognized according to the rules of any formal system of chemical nomenclature such as IUPAC inorganic or IUPAC organic nomenclature. A ...

for a very large

polycyclic aromatic hydrocarbon A polycyclic aromatic hydrocarbon (PAH) is a class of organic compounds that is composed of multiple aromatic rings. The simplest representative is naphthalene, having two aromatic rings and the three-ring compounds anthracene and phenanthrene. ...

. Its formal name is benzo 0,11henanthro ',3',4',5',6':4,5,6,7hryseno ,2,3-''bc''oronene (

IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...

name) or benzo ,2,3-''bc'':4,5,6-b'c'icoronene (name sometimes used in

Chemical Abstracts CAS (formerly Chemical Abstracts Service) is a division of the American Chemical Society. It is a source of chemical information. CAS is located in Columbus, Ohio, United States. Print periodicals ''Chemical Abstracts'' is a periodical index tha ...

). It has 15 rings and is a brick-red solid. Its formula is . Dicoronylene sublimes under high vacuum, 0.001

torr The torr (symbol: Torr) is a unit of pressure based on an absolute scale, defined as exactly of a standard atmosphere (). Thus one torr is exactly (≈ ). Historically, one torr was intended to be the same as one " millimeter of merc ...

, between 250 °C and 300 °C.

Structure

Due to its large size and limited availability, the organic chemistry of dicoronylene is little known. Dicoronylene does undergo a Diels–Alder reaction with

maleic anhydride Maleic anhydride is an organic compound with the formula C2H2(CO)2O. It is the acid anhydride of maleic acid. It is a colorless or white solid with an acrid odor. It is produced industrially on a large scale for applications in coatings and pol ...

on one or both of the central bay regions on either side of the bridging ring. The

double bond In chemistry, a double bond is a covalent bond between two atoms involving four bonding electrons as opposed to two in a single bond. Double bonds occur most commonly between two carbon atoms, for example in alkenes. Many double bonds exist betwee ...

of maleic anhydride forms two

carbon–carbon bond A carbon–carbon bond is a covalent bond between two carbon atoms. The most common form is the single bond: a bond composed of two electrons, one from each of the two atoms. The carbon–carbon single bond is a sigma bond and is formed bet ...

s on the ends of the bay region, making a new six-membered ring. Heating removes the anhydride as

carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...

gas and gives the corresponding 16-ring and 17-ring PAHs.

Occurrence

Dicoronylene was first observed in the solid residue produced in coal gasification. This residue contained large amounts of

coronene Coronene (also known as superbenzene and cyclobenzene) is a polycyclic aromatic hydrocarbon (PAH) comprising seven peri-fused benzene rings. Its chemical formula is . It is a yellow material that dissolves in common solvents including benzene, tol ...

and

ovalene Ovalene is a polycyclic aromatic hydrocarbon with the formula C32H14, which consists of ten peri-fused six-membered rings. It is very similar to coronene. Ovalene is a reddish-orange compound. It is sparingly soluble in solvents such as benzene, ...

. After these were extracted and identified, a reddish residue remained, which was sparingly soluble in organic solvents. Elemental analysis indicated that it was most likely the condensed dimer of

. Dicoronylene was later discovered to occur as a by-product of the catalytic hydrocracking used in petroleum processing. It is formed when two

molecules fuse. It is estimated that catalytical hydrocracking produces several hundred metric tons of dicoronylene worldwide per year, making it the most prevalent large PAH. In this process, the analogous 18-ring PAH formed from coronene and ovalene () is also formed in 1% to 20% proportions. It is purple in color.

Properties

The formation of dicoronylene in hydrocracking reactors is a serious problem because its low solubility make it precipitate in any cooler part of the reactor flow path. This causes plugging of flow lines that require periodic shutdown and removal of the reddish deposits. Dicoronylene is also a constituent of coke formed on hydrocracking catalysts, which reduces their activity. Thermal

pyrolysis The pyrolysis (or devolatilization) process is the thermal decomposition of materials at elevated temperatures, often in an inert atmosphere. It involves a change of chemical composition. The word is coined from the Greek-derived elements ''py ...

shows masses of dicoronylene and the condensed trimer, tetramer, and pentamer in the

mass spectrum A mass spectrum is a histogram plot of intensity vs. ''mass-to-charge ratio'' (''m/z'') in a chemical sample, usually acquired using an instrument called a ''mass spectrometer''. Not all mass spectra of a given substance are the same; for example ...

of the black product. These larger coronene condensates are black in color. Dicoronylene is moderately soluble in

1,2,4-trichlorobenzene 1,2,4-Trichlorobenzene is an organochlorine compound, one of three isomers of trichlorobenzene. It is a derivative of benzene with three chloride substituents. It is a colorless liquid used as a solvent for a variety of compounds and materials. ...

and these solutions have a greenish yellow

fluorescence Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, tha ...

. Unlike coronene, dicoronylene has symmetrical fluorescence excitation and emission spectra. It is virtually insoluble in most solvents. Dicoronylene has been studied as a model for interstellar PAHs. Its large size and planarity have also shown promise as a chromatographic separation material.

References

{{PAHs Polycyclic aromatic hydrocarbons