Ethylene dione or ethylenedione, also called dicarbon dioxide, ethenedione, or ethene 1,2-dione, is the name given to a hypothetical chemical compound with the formula C2O2 or O=C=C=O. It would be an oxide of carbon (an oxocarbon), specifically a dimer of carbon monoxide (CO). It can be thought of as ketene of glyoxylic acid (OHCCOOH).
Early theoretical studies suggested that the triplet state of C2O2 might be stable, although it would be much less so than its relatives CO2 and C3O2. However, many synthesis attempts have failed to turn up any trace of it. Recent research indicates that the molecule may be extremely short lived, decomposing into two molecules of carbon monoxide in less than 10−8 seconds.
On the other hand, the divalent anion C2O22−, called acetylenediolate, is reasonably stable in the absence of water.
Koch's glyoxylide 
In the 1940s, Detroit physician William Frederick Koch claimed that he had synthesized this compound, which he called glyoxylide, and that it was an antidote to the toxins that caused a long list of ailments, including diabetes and cancer. Neither claim was ever confirmed, and the drug was classified as a fraud by the FDA.
See also