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 any member of a class of organic compounds that is composed of multiple fused aromatic rings. Most are produced by the incomplete combustion of organic matter— by engine exhaust fumes, tobacco, incine ...

. 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 Pressure#Units, unit of pressure based on an absolute scale, defined as exactly of a standard atmosphere (unit), atmosphere (101325 Pa). Thus one torr is exactly (≈ ). Historically, one torr was intended to be ...

, 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 In organic chemistry, the Diels–Alder reaction is a chemical reaction between a Conjugated system, conjugated diene and a substituted alkene, commonly termed the Diels–Alder reaction#The dienophile, dienophile, to form a substituted cyclohexe ...

with

maleic anhydride Maleic anhydride is an organic compound with the formula . 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 polymers. Str ...

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 betw ...

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 between on ...

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

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

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

Occurrence

Dicoronylene was first observed in the solid residue produced in coal

gasification Gasification is a process that converts biomass- or fossil fuel-based carbonaceous materials into gases, including as the largest fractions: nitrogen (N2), carbon monoxide (CO), hydrogen (H2), and carbon dioxide (). This is achieved by reacting ...

. 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. 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 In petrochemistry, petroleum geology and organic chemistry, cracking is the process whereby complex organic molecules such as kerogens or long-chain hydrocarbons are broken down into simpler molecules such as light hydrocarbons, by the breaking ...

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 Pyrolysis is a process involving the Bond cleavage, separation of covalent bonds in organic matter by thermal decomposition within an Chemically inert, inert environment without oxygen. Etymology The word ''pyrolysis'' is coined from the Gree ...

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. P ...

and these solutions have a greenish yellow

fluorescence Fluorescence is one of two kinds of photoluminescence, the emission of light by a substance that has absorbed light or other electromagnetic radiation. When exposed to ultraviolet radiation, many substances will glow (fluoresce) with colore ...

. 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