Dicarbonate

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. These compounds can be viewed as derivatives of the hypothetical compound dicarbonic acid, HO−C(=O)−O−C(=O)−OH or H2C2O5. Two important organic compounds containing this group are dimethyl dicarbonate H3C−C2O5−CH3 and di-tert-butyl dicarbonate (H3C−)3C−C2O5−C(−CH3)3.

Not to be confused with Bicarbonate.
Dicarbonate ion
Names
IUPAC name
Dicarbonate
Other names
Pyrocarbonate
Identifiers
3D model (JSmol)
MeSH pyrocarbonate
  • InChI=1S/C2H2O5/c3-1(4)7-2(5)6/h(H,3,4)(H,5,6)/p-2
    Key: ZFTFAPZRGNKQPU-UHFFFAOYSA-L
  • C(=O)([O-])OC(=O)[O-]
Properties
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.[2]

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 Å3 and density 7.59.[3]

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 Å3 and density 4.61.[3] 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.[4]

See also

References
  1. Plácido García; Helge Willner; Maximiliano Burgos Paci; Gustavo A. Argüello; Thorsten Berends (2005). "Bis(trifluoromethyl)dicarbonate, CF3OC(O)OC(O)OCF3". J. Fluorine Chem. 126 (6): 984–990. doi:10.1016/j.jfluchem.2005.05.002.
  2. Zeller, Klaus-Peter; Schuler, Paul; Haiss, Peter (2005). "The hidden equilibrium in aqueous sodium carbonate solutions: Evidence for the formation of the dicarbonate anion". Eur. J. Inorg. Chem. 2005 (1): 168–172. doi:10.1002/ejic.200400445.
  3. Spahr, Dominik; König, Jannes; Bayarjargal, Lkhamsuren; Luchitskaia, Rita; Milman, Victor; Perlov, Alexander; Liermann, Hanns-Peter; Winkler, Björn (22 June 2022). "Synthesis and Structure of Pb[C2O5]: An Inorganic Pyrocarbonate Salt". Inorganic Chemistry. 61 (26): 9855–9859. doi:10.1021/acs.inorgchem.2c01507. PMID 35730801. S2CID 249922854.
  4. Spahr, Dominik; König, Jannes; Bayarjargal, Lkhamsuren; Milman, Victor; Perlov, Alexander; Liermann, Hanns-Peter; Winkler, Björn (23 February 2022). "Sr[C2O5 ] is an Inorganic Pyrocarbonate Salt with [C 2 O 5 ] 2– Complex Anions". Journal of the American Chemical Society. 144 (7): 2899–2904. doi:10.1021/jacs.2c00351. PMID 35134291. S2CID 246678040.
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