Hydrogenoxalate

Hydrogenoxalate or hydrogen oxalate (IUPAC name: 2-Hydroxy-2-oxoacetate) is an anion with chemical formula HC₂O−4 or HO−C(=O)−CO−2, derived from oxalic acid by the loss of a single proton; or, alternatively, from the oxalate anion C₂O2−4 by addition of a proton. The name is also used for any salt containing this anion. Especially in older literature, hydrogenoxalates may also be referred to as bioxalates, acid oxalates, or monobasic oxalates. Hydrogenoxalate is amphoteric, in that it can react both as an acid or a base.

Hydrogenoxalate

Names
IUPAC name 2-Hydroxy-2-oxoacetate[1]
Systematic IUPAC name 2-Hydroxy-2-oxoethanoate
Other names Bioxalate Hydrogen oxalate Hydrogenoxalate
Identifiers
CAS Number	920-52-5 N
3D model (JSmol)	Interactive image
Beilstein Reference	3601755
ChEBI	CHEBI:46904
Gmelin Reference	49515
PubChem CID	3716971
CompTox Dashboard (EPA)	DTXSID8043785
InChI InChI=1S/C2H2O4/c3-1(4)2(5)6/h(H,3,4)(H,5,6)/p-1 Key: MUBZPKHOEPUJKR-UHFFFAOYSA-M
SMILES C(=O)(C(=O)[O-])O
Properties
Chemical formula	HC2O−4
Molar mass	89.026 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

Well characterized salts include sodium hydrogenoxalate (NaHC₂O₄),^[2][3] potassium hydrogenoxalate (KHC₂O₄),^[4] ammonium hydrogenoxalate ([NH₄]⁺HC₂O−4), rubidium hydrogenoxalate (RbHC₂O₄)^[5] and dimethylammonium hydrogenoxalate ([(CH₃)₂NH]⁺HC₂O−4).^[6]

Structure

Most hydrogenoxalate salts are hydrated. For example, potassium hydrogen oxalate crystallizes as 2KHC₂O₄·H₂O. These materials exhibit extended structures resulting from extensive hydrogen bonding and anion-cation interactions. The hydrates dehydrate upon heating:^[4]

2KHC₂O₄·H₂O → 2 KHC₂O₄ + H₂O

Proton transfer in hydrogen oxalates has been studied.^[7]

See also

• Bicarbonate

References

1. "Hydrogen oxalate".
2. Tellgren, Roland; Olovsson, Ivar (1971). "The crystal structures of normal and deuterated sodium hydrogen oxalate monohydrate NaHC₂O₄·H₂O and NaDC₂O₄·D₂O. Hydrogen bond studies XXXVI". The Journal of Chemical Physics. 54 (1): 127–134. Bibcode:1971JChPh..54..127T. doi:10.1063/1.1674582.
3. Delaplane, R. G.; Tellgren, R.; Olovsson, I. (1984). "Neutron diffraction study of sodium hydrogen oxalate monohydrate, NaHC₂O₄·H₂O, at 120 K". Acta Crystallographica. C40 (11): 1800–1803. Bibcode:1984AcCrC..40.1800D. doi:10.1107/S0108270184009616.
4. Hume, J.; Colvin, J. (1929). "The decomposition of potassium hydrogen oxalate hemihydrate". Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character. 125 (799). The Royal Society: 635–646. Bibcode:1929RSPSA.125..635H. doi:10.1098/rspa.1929.0192. ISSN 0950-1207.
5. Hamadène, M.; Kherfi, H.; Guehria-Laidoudi, A. (2006). "The polymeric anhydrous rubidium hydrogen oxalate". Acta Crystallographica. A62: s280. Bibcode:2006AcCrA..62R.280H. doi:10.1107/S0108767306094414.
6. Diallo, Waly; Gueye, Ndongo; Crochet, Aurélien; Plasseraud, Laurent; Cattey, Hélène (11 April 2015). "Crystal structure of dimethylammonium hydrogen oxalate hemi(oxalic acid)". Acta Crystallographica Section E: Crystallographic Communications. 71 (5). International Union of Crystallography (IUCr): 473–475. Bibcode:2015AcCrE..71..473D. doi:10.1107/s2056989015005964. ISSN 2056-9890. PMC 4420082. PMID 25995858.
7. Bosch, Enric; Moreno, Miquel; Lluch, José María (1 January 1992). "The role of coupling in intramolecular proton transfer reactions. The hydrogen oxalate anion as an example". Canadian Journal of Chemistry. 70 (1). Canadian Science Publishing: 100–106. doi:10.1139/v92-017. ISSN 0008-4042.