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
ChemSpider	2948058
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