Pentacarbon dioxide

Pentacarbon dioxide, officially penta-1,2,3,4-tetraene-1,5-dione, is an oxide of carbon (an oxocarbon) with formula C5O2 or O=C=C=C=C=C=O.

The compound was described in 1988 by Günter Maier and others, who obtained it by pyrolysis of cyclohexane-1,3,5-trione (phloroglucin, the tautomeric form of phloroglucinol).[1] It has also been obtained by flash vapor pyrolysis of 2,4,6-tris(diazo)cyclohexane-1,3,5-trione (C6N6O3).[2]:p.97 It is stable at room temperature in solution.[1] The pure compound is stable up to −96 °C, at which point it polymerizes.[2]

Pentacarbon dioxide
Full structural formula of pentacarbon dioxide
Space-filling model of the pentacarbon dioxide molecule
IUPAC name
3D model (JSmol)
Molar mass 92.05 g/mol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).


  1. ^ a b Maier, G.; Reisenauer, H. P.; Schäfer, U.; Balli, H. (1988). "C5O2 (1,2,3,4-Pentatetraene-1,5-dione), a New Oxide of Carbon". Angewandte Chemie International Edition. 27 (4): 566–568. doi:10.1002/anie.198805661.
  2. ^ a b Eastwood, F. W. (1997). "Gas Phase Pyrolytic Methods for the Preparation of Carbon-Hydrogen and Carbon-Hydrogen-Oxygen Compounds". In Vallée, Y. (ed.). Gas Phase Reactions in Organic Synthesis. CRC Press. ISBN 90-5699-081-0.

See also

Carbon suboxide

Carbon suboxide, or tricarbon dioxide, is an oxide of carbon with chemical formula C3O2 or O=C=C=C=O. Its four cumulative double bonds make it a cumulene. It is one of the stable members of the series of linear oxocarbons O=Cn=O, which also includes carbon dioxide (CO2) and pentacarbon dioxide (C5O2). Although if carefully purified it can exist at room temperature in the dark without decomposing, it will polymerize under certain conditions.

The substance was discovered in 1873 by Benjamin Brodie by subjecting carbon monoxide to an electric current. He claimed that the product was part of a series of "oxycarbons" with formulas Cx+1Ox, namely C2O, C3O2, C4O3, C5O4, ..., and to have identified the last two; however only C3O2 is known. In 1891 Marcellin Berthelot observed that heating pure carbon monoxide at about 550 °C created small amounts of carbon dioxide but no trace of carbon, and assumed that a carbon-rich oxide was created instead, which he named "sub-oxide". He assumed it was the same product obtained by electric discharge and proposed the formula C2O. Otto Diels later stated that the more organic names dicarbonylmethane and dioxallene were also correct.

It is commonly described as an oily liquid or gas at room temperature with an extremely noxious odor.


An oxocarbon or oxide of carbon is a chemical compound consisting only of carbon and oxygen.The simplest and most common oxocarbons are carbon monoxide (CO) and carbon dioxide (CO2) with IUPAC names carbon(II) oxide and carbon(IV) oxide respectively. Many other stable (practically if not thermodynamically) or metastable oxides of carbon are known, but they are rarely encountered, such as carbon suboxide (C3O2 or O=C=C=C=O) and mellitic anhydride (C12O9).

While textbooks will often list only the first three, and rarely the fourth, a large number of other oxides are known today, most of them synthesized since the 1960s. Some of these new oxides are stable at room temperature. Some are metastable or stable only at very low temperatures, but decompose to simpler oxocarbons when warmed. Many are inherently unstable and can be observed only momentarily as intermediates in chemical reactions or are so reactive that they can exist only in the gas phase or under matrix isolation conditions.

The inventory of oxocarbons appears to be steadily growing. The existence of graphene oxide and of other stable polymeric carbon oxides with unbounded molecular structures suggests that many more remain to be discovered.


Phloroglucinol is an organic compound with the formula C6H3(OH)3. It is a colorless solid. It is used in the synthesis of pharmaceuticals and explosives. Phloroglucinol is one of three isomeric benzenetriols. The other two isomers are hydroxyquinol (1,2,4-benzenetriol) and pyrogallol (1,2,3-benzenetriol). Phloroglucinol, and its benzenetriol isomers, are still defined as "phenols" according to the IUPAC official nomenclature rules of chemical compounds. Many such monophenolics are often termed "polyphenols" by the cosmetic and parapharmaceutical industries, but they cannot be by any scientifically-accepted definition.

Tetracarbon dioxide

Tetracarbon dioxide is an oxide of carbon, a chemical compound of carbon and oxygen, with chemical formula C4O2 or O=C=C=C=C=O. It can be regarded as butatriene dione, the double ketone of butatriene — more precisely 1,2,3-butatriene-1,4-dione.Butatriene dione is the fourth member of the family of linear carbon dioxides O(=C)n=O, that includes carbon dioxide CO2 or O=C=O, ethylene dione C2O2 or O=C=C=O, carbon suboxide C3O2 or O=C=C=C=O, pentacarbon dioxide C5O2 or O=C=C=C=C=C=O, and so on.

The compound was obtained in 1990 by Maier and others, by flash vacuum pyrolysis of cyclic azaketones in a frozen argon matrix. It was also obtained in the same year by Sülzle and Schwartz through impact ionization of ((CH3-)2(C4O2)(=O)2=)2 in the gas phase. Although theoretical studies indicated that the even-numbered members of the O(=C)n=O family should be inherently unstable, C4O2 is indefinitely stable in the matrix, but is decomposed by light into tricarbon monoxide C3O and carbon monoxide CO. It has a triplet ground state.

Common oxides
Exotic oxides
Compounds derived from oxides


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