Potassium hydrogenoxalate

Potassium hydrogenoxalate is a salt with formula KHC₂O₄ or K⁺·HO₂C-CO₂⁻. It is one of the most common salts of the hydrogenoxalate anion, and can be obtained by reacting potassium hydroxide with oxalic acid in 1:1 mole ratio.

Potassium hydrogenoxalate

Names
IUPAC name Potassium 2-hydroxy-2-oxoacetate
Other names Potassium bioxalate
Identifiers
CAS Number	127-95-7 Y
3D model (JSmol)	Interactive image
ChemSpider	29125 N
ECHA InfoCard	100.004.431
PubChem CID	31394
UNII	L3W2519LG2 Y
CompTox Dashboard (EPA)	DTXSID6059572
InChI InChI=1S/C2H2O4.K/c3-1(4)2(5)6;/h(H,3,4)(H,5,6);/q;+1/p-1 N Key: JMTCDHVHZSGGJA-UHFFFAOYSA-M N InChI=1/C2H2O4.K/c3-1(4)2(5)6;/h(H,3,4)(H,5,6);/q;+1/p-1 Key: JMTCDHVHZSGGJA-REWHXWOFAF
SMILES [K+].[O-]C(=O)C(=O)O
Properties
Chemical formula	C2HKO4
Molar mass	128.124 g·mol−1
Appearance	White crystalline solid
Odor	odorless
Density	2.0 g/cm3
Solubility in water	2.5 g/100 g
Solubility	slightly soluble in alcohol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

The salt is also known as: potassium hydrogen oxalate, potassium bioxalate, acid potassium oxalate, or monobasic potassium oxalate. In older literature, it was also called: Salt of sorrel,^[1] sorrel salt, sel d'oseille,^[2][3] sal acetosella; or, inaccurately, salt of lemon (due to the similar acidic “lemony” taste of the edible common sorrel or garden sorrel)^[4]

Potassium hydrogenoxalate occurs in some plants, notably sorrel. It is a commercial product used in photography, marble grinding, and removing ink stains.

Properties

The anhydrous product is a white, odorless, crystalline solid, hygroscopic and soluble in water (2.5 g/100 g at room temperature). The solutions are basic. Below 50 °C the much less soluble "potassium tetraoxalate" K⁺[C₂HO₄]⁻·C₂H₂O₄ forms and precipitates out of solution.^[5]

The monohydrate KHC₂O₄·H₂O starts losing the water at 100 °C.^[6]

The anhydrous salt was found to have remarkable elastic anisotropy, due to its crystal structure that consists of relatively rigid columns of hydrogen-bonded hydrogenoxalate anions, joined into sheets by ionic K–O bonds.^[7]

Toxicity

Potassium hydrogenoxalate is strongly irritating to eyes, mucoses and gastrointestinal tract. It may cause cardiac failure and death.^[5]

See also

• Potassium bicarbonate
• Potassium hydrogenacetylenedicarboxylate