Dicarbonate

Not to be confused with Bicarbonate.

A dicarbonate, also known as a pyrocarbonate, is a chemical containing the divalent −O−C(=O)−O−C(=O)−O− or −C₂O₅− functional group, which consists of two carbonate groups sharing an oxygen atom. It is one of polycarbonate functional groups. These compounds can be viewed as derivatives of the hypothetical compound dicarbonic acid,^[2] HO−C(=O)−O−C(=O)−OH or H₂C₂O₅. Three important organic compounds containing this group are:

• dimethyl dicarbonate H₃C−C₂O₅−CH₃
• diethyl dicarbonate C₂H₅−C₂O₅−C₂H₅
• di-tert-butyl dicarbonate (H₃C−)₃C−C₂O₅−C(−CH₃)₃, also known as Boc anhydride.

Dicarbonate ion

Names
IUPAC name Dicarbonate
Other names Pyrocarbonate
Identifiers
CAS Number	214335-04-3 Y
3D model (JSmol)	Interactive image
ChemSpider	10616988
MeSH	pyrocarbonate
PubChem CID	15238643
CompTox Dashboard (EPA)	DTXSID30570367
InChI InChI=1S/C2H2O5/c3-1(4)7-2(5)6/h(H,3,4)(H,5,6)/p-2 Key: ZFTFAPZRGNKQPU-UHFFFAOYSA-L
SMILES C(=O)([O-])OC(=O)[O-]
Properties
Chemical formula	C2O2−5
Molar mass	104.017 g·mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

The general structure of dicarbonate esters

Molecular structure of bis(trifluoromethyl) dicarbonate^[1]

It is one of the oxocarbon anions, consisting solely of oxygen and carbon. The anion has the formula ⁻O−C(=O)−O−C(=O)−O⁻ or C₂O2−5. Dicarbonate salts are apparently unstable at ambient conditions, but can be made under pressure and may have a fleeting existence in carbonate solutions.^[3]

The term dicarbonate is sometimes used erroneously to refer to bicarbonate, the common name of the hydrogencarbonate anion HCO−3 or esters of the hydrogencarbonate functional group −O−C(=O)−OH. It is also sometimes used for chemicals that contain two carbonate units in their covalent structure or stoichiometric formula.

Inorganic salts

PbC₂O₅ (lead(II) dicarbonate) can be formed at 30 GPa and 2000K from PbCO₃ and CO₂. It forms white monoclinic crystals, with space group P2₁/c and four formula units per unit cell. At 30 GPa the unit cell has a=4.771 b=8.079 c=7.070 Å and β=91.32°. The unit cell volume is 272.4 ų and density 7.59.^[4]

SrC₂O₅ (strontium dicarbonate) is very similar to the lead compound, and also has monoclinic structure with space group P2₁/c and four formula units per unit cell. At 30 GPa the unit cell has a=4.736 b=8.175 c=7.140 Å and β=91.34°. The unit cell volume is 276.3 ų and density 4.61.^[4] The double Sr=O bonds have lengths of 1.22, 1.24, and 1.25 Å. The single Sr-O bonds have lengths of 1.36 and 1.41 Å. The angles subtended at the carbon atoms are slightly less than 120°, and the angle at the C-O-C is larger.^[5]

See also

• Tricarbonate
• Peroxodicarbonate
• Oxalate
• Pyrosulfate
• Peroxydisulfate
• Dithionate
• Trithionate
• Tetrathionate
• Pyrophosphate
• Polyphosphate