Potassium hydrogenoxalate

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Potassium hydrogenoxalate
Monopotassium oxalate.png
IUPAC name
Potassium 2-hydroxy-2-oxoacetate
Other names
Potassium bioxalate
3D model (JSmol)
ECHA InfoCard 100.004.431
Molar mass 128.124 g·mol−1
Appearance White crystalline solid
Odor odorless
Density 2.0 g/cm3
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).
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Infobox references

Potassium hydrogenoxalate, also known as potassium bioxalate, 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.

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; see sorrel below).[4]

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


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 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]


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

See also[edit]


  1. ^ "Die Net Dictionary: "Salt of Sorrel"". Retrieved 19 May 2012. (retrieved via Internet Archive)
  2. ^ "Selency: Old bottle at pharmacy—'Salt of Sorrel'". Salt of Sorrel labelled “sel d'oseille”.
  3. ^ "Salt of Sorrel: labelled 'sel d'oseille'". Old dark-amber glass vial marked “sel d'oseille” with protective leaden cap.
  4. ^ "kitchn™ It's Fresh, Green, and Super Tangy: Sorrel Is In Season!". “This fresh, “lemony” sourness has been highly prized in cuisines all over the world.”
  5. ^ a b ChemicalBook (2007) Potassium binoxalate Product Description
  6. ^ Mark Dugan (2009) Potassium binoxalate product data sheet. Hummel Croton Inc.
  7. ^ H. Koppers (1973), 'The Elastic Constants of Monoclinic Potassium Hydrogen Oxalate Acta Crystallographica,volume A29, p. 415.