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In organic chemistry, a dicarbonate, also known as a pyrocarbonate, is a compound containing the divalent [−O−(C=O)−O−(C=O)−O−] or −C
2O
5− functional group, which consists of two carbonate groups sharing an oxygen atom. These compounds can be viewed as double esters of a hypothetical dicarbonic acid, H
2C
2O
5 or HO−(C=O)−O−(C=O)−OH. Two important examples are dimethyl dicarbonate H3C−C2O5−CH3 and di-tert-butyl dicarbonate (H3C−)3C−C2O5−C(−CH3)3.
It is one of the oxocarbon anions, consisting solely of oxygen and carbon. Dicarbonate salts are apparently unstable but may have a fleeting existence in carbonate solutions.
The term "dicarbonate" is sometimes used erroneously to refer to bicarbonate, the common name of the hydrogencarbonate anion HCO3− or organic group the ROCO2H.