Carbon suboxide

Carbon suboxide, or tricarbon dioxide, is an organic, oxygen-containing chemical compound with formula C₃O₂ and structure 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 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.