Carbon suboxide

Overview
Carbon suboxide, or tricarbon dioxide, C3O2, is a colorless pungent gas, with four cumulative double bonds, making it a cumulene. It is closely related to CO, CO2 and C2O, and other oxides of carbon.

Brodie discovered it in 1873 by submitting electric current to carbon monoxide. Marcellin Berthelot created the name carbon suboxide, while Otto Diels later stated that the more organic names dicarbonyl methane and dioxallene were also correct.

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. Malonic anhydride (not the be confused with maleic anhydride) is a real molecule.

Several other ways for synthesis and reactions of carbon suboxide can be found in a review from 1930 by Reyerson.

Carbon suboxide polymerizes spontaneously to a red, yellow, or black solid. The structure is postulated to be poly(α-pyronic), similar to the structure in 2-Pyrone (α-Pyrone). In 1969, it was proposed that the color of Martian surface is attributed to this compound, it was proven to be a wrong concept after the Viking mission.