Carbon suboxide

Carbon suboxide

Names
IUPAC name 1,2-Propadiene-1,3-dione
Identifiers
CAS Number	504-64-3 Y
3D model (Jmol)	Interactive image
ChEBI	CHEBI:30086 Y
ChemSpider	120106 Y
MeSH	Carbon+suboxide
PubChem CID	136332
InChI InChI=1S/C3O2/c4-2-1-3-5 Y Key: GNEVIACKFGQMHB-UHFFFAOYSA-N Y InChI=1S/C3O2/c4-2-1-3-5 Key: GNEVIACKFGQMHB-UHFFFAOYSA-N InChI=1/C3O2/c4-2-1-3-5 Key: GNEVIACKFGQMHB-UHFFFAOYAU
SMILES O=C=C=C=O
Properties
Chemical formula	C3O2
Molar mass	68.03 g·mol−1
Appearance	colorless gas
Odor	strong, pungent odor
Density	0.906 ± 0.06 g cm−3, gas at 298 K
Melting point	−111.3 °C (−168.3 °F; 161.8 K)
Boiling point	6.8 °C (44.2 °F; 279.9 K)
Solubility in water	reacts
Solubility	soluble in 1,4-dioxane, ether, xylene, CS2, tetrahydrofuran
Refractive index (nD)	1.4538 (6 °C)
Dipole moment	0 D
Structure
Crystal structure	rhombic
Molecular shape	quasilinear (phase dependent)
Thermochemistry
Specific heat capacity (C)	66.99 J/mol K
Std molar entropy (So298)	276.1 J/mol K
Std enthalpy of formation (ΔfHo298)	-93.6 kJ/mol
Related compounds
Related oxides	carbon dioxide carbon monoxide dicarbon monoxide
Related compounds	carbon subsulfide carbon subnitride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Y  (what is YN ?)
Infobox references

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=C_n=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 C_x+1O_x, namely C, 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.

It is synthesized by warming a dry mixture of phosphorus pentoxide (P₄O₁₀) and malonic acid or the esters of malonic acid. Therefore, it can be also considered as the anhydride of malonic anhydride, i.e. the "second anhydride" of malonic acid.