1,3-Dioxetanedione

The chemical compound 1,3-dioxetanedione, or 1,3-dioxacyclobutane-2,4-dione, also known as dicarbonic anhydride, is a hypothetical oxide of carbon with formula C2O4. It can be considered a cyclic dimer of carbon dioxide (CO2) or as a double ketone of 1,3-dioxetane (1,3-dioxacyclobutane).

Theoretical calculations indicate that the compound would be extremely unstable at room temperature (half-life of less than 1.1 μs) but may be stable at −196 °C.