Sodium oxalate, or disodium oxalate, is the

sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable iso ...

salt of

oxalic acid Oxalic acid is an organic acid with the systematic name ethanedioic acid and formula . It is the simplest dicarboxylic acid. It is a white crystalline solid that forms a colorless solution in water. Its name comes from the fact that early inve ...

with the formula Na₂C₂O₄. It is a white, crystalline, odorless solid, that decomposes above 290

°C The degree Celsius is the unit of temperature on the Celsius scale (originally known as the centigrade scale outside Sweden), one of two temperature scales used in the International System of Units (SI), the other being the Kelvin scale. The ...

. Disodium oxalate can act as a

reducing agent In chemistry, a reducing agent (also known as a reductant, reducer, or electron donor) is a chemical species that "donates" an electron to an (called the , , , or ). Examples of substances that are commonly reducing agents include the Earth meta ...

, and it may be used as a

primary standard A primary standard in metrology is a standard that is sufficiently accurate such that it is not calibrated by or subordinate to other standards. Primary standards are defined via other quantities like length, mass and time. Primary standards are u ...

for standardizing

potassium permanganate Potassium permanganate is an inorganic compound with the chemical formula KMnO4. It is a purplish-black crystalline salt, that dissolves in water as K+ and , an intensely pink to purple solution. Potassium permanganate is widely used in the c ...

(KMnO₄) solutions. The

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. ( ...

form of sodium oxalate is natroxalate. It is only very rarely found and restricted to extremely sodic conditions of ultra-alkaline

pegmatite A pegmatite is an igneous rock showing a very coarse texture, with large interlocking crystals usually greater in size than and sometimes greater than . Most pegmatites are composed of quartz, feldspar, and mica, having a similar silicic com ...

Preparation

Sodium oxalate can be prepared through the neutralization of

with sodium hydroxide (NaOH) in a 1:2 acid-to-base molar ratio. Evaporation yields the anhydrous oxalateH. W. Foote and John E. Vance (1933), "The system; sodium iodate, sodium oxalate, water". ''American Journal of Science'', series 5, volume 26, issue 151, pages 16-18. that can be thoroughly dried by heating to between 200 and 250 °C. Half-neutralization can be accomplished with NaOH in a 1:1 ratio which produces NaHC₂O₄, monobasic sodium oxalate or

sodium hydrogenoxalate Sodium hydrogenoxalate is salt (ionic compound) of formula , consisting of sodium cations and hydrogenoxalate anions or . The anion can be described as the result of removing one hydrogen ion from oxalic acid , or adding one to the oxalate a ...

. Alternatively, it can be produced by decomposing

sodium formate Sodium formate, HCOONa, is the sodium salt of formic acid, HCOOH. It usually appears as a white deliquescent powder. Preparation For commercial use, sodium formate is produced by absorbing carbon monoxide under pressure in solid sodium hydroxid ...

by heating it at a temperature exceeding 360 °C.

Reactions

Sodium oxalate starts to decompose above 290 °C into

sodium carbonate Sodium carbonate, , (also known as washing soda, soda ash and soda crystals) is the inorganic compound with the formula Na2CO3 and its various hydrates. All forms are white, odourless, water-soluble salts that yield moderately alkaline solutions ...

and

carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...

:Yoshimori T1, Asano Y, Toriumi Y, Shiota T. (1978) "Investigation on the drying and decomposition of sodium oxalate". ''Talanta'', volume 25, issue 10, pages 603-605. : → + When heated at between 200 and 525°C with

vanadium pentoxide Vanadium(V) oxide (''vanadia'') is the inorganic compound with the formula V2 O5. Commonly known as vanadium pentoxide, it is a brown/yellow solid, although when freshly precipitated from aqueous solution, its colour is deep orange. Because o ...

in a 1:2 molar ratio, the above reaction is suppressed, yielding instead a

sodium vanadium oxibronze Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable is ...

with release of

carbon dioxide Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...

D. Ballivet-Tkatchenko, J. Galy, -M. Savariault (1994): "Thermal decomposition of sodium oxalate in the presence of V2O5: Mechanistic approach of sodium oxibronzes formation". '' Thermochimica Acta'', volume 232, issue 2, pages 215-223. : ''x'' + 2 → 2 + 2''x'' with ''x'' increasing up to 1 as the temperature increases. Sodium oxalate is used to standardize

solutions. It is desirable that the temperature of the titration mixture be greater than 60 °C to ensure that all the permanganate added reacts quickly. The kinetics of the reaction are complex, and the manganese(II) ions formed catalyze the further reaction between permanganate and oxalic acid (formed ''in situ'' by the addition of excess sulfuric acid). The final equation is as follows: : 5 Na₂C₂O₄ + 2 KMnO₄ + 8 H₂SO₄ → K₂SO₄ + 5 Na₂SO₄ + 2 MnSO₄ + 10 CO₂ + 8 H₂O

Biological activity

Like several other

oxalate Oxalate (IUPAC: ethanedioate) is an anion with the formula C2O42−. This dianion is colorless. It occurs naturally, including in some foods. It forms a variety of salts, for example sodium oxalate (Na2C2O4), and several esters such as dimethyl o ...

s, sodium oxalate is toxic to humans. It can cause burning pain in the mouth, throat and stomach, bloody vomiting, headache, muscle cramps, cramps and convulsions, drop in blood pressure, heart failure, shock, coma, and possible death. Mean lethal dose by ingestion of oxalates is 10-15 grams/kilogram of body weight (per

MSDS A safety data sheet (SDS), material safety data sheet (MSDS), or product safety data sheet (PSDS) is a document that lists information relating to occupational safety and health for the use of various substances and products. SDSs are a widely ...

). Sodium oxalate, like

citrate Citric acid is an organic compound with the chemical formula HOC(CO2H)(CH2CO2H)2. It is a colorless weak organic acid. It occurs naturally in citrus fruits. In biochemistry, it is an intermediate in the citric acid cycle, which occurs in t ...

s, can also be used to remove calcium ions (Ca²⁺) from blood plasma. It also prevents blood from clotting. Note that by removing calcium ions from the blood, sodium oxalate can impair brain function, and deposit

calcium oxalate Calcium oxalate (in archaic terminology, oxalate of lime) is a calcium salt of oxalic acid with the chemical formula . It forms hydrates , where ''n'' varies from 1 to 3. Anhydrous and all hydrated forms are colorless or white. The monohydrate ...

in the kidneys.

References

{{Oxalates Oxalates Sodium compounds