|Preferred IUPAC name|
|Systematic IUPAC name|
|Other names |
Wood bleach, Crab Acid
3D model (JSmol)
|ECHA InfoCard|| 100.005.123 |
CompTox Dashboard (EPA)
|Molar mass||90.034 g·mol−1|
126.065 g·mol−1 (dihydrate)
|Density||1.90 g·cm−3 (anhydrous, at 17 °C) |
1.653 g·cm−3 (dihydrate)
|Melting point||189 to 191 °C (372 to 376 °F; 462 to 464 K)|
101.5 °C (214.7 °F; 374.6 K) dihydrate
|90-100 g/L (20 °C)|
|Solubility||237 g/L (15 °C) in ethanol |
14 g/L (15 °C) in diethyl ether
|Vapor pressure||<0.001 mmHg (20 °C)|
|Acidity (pKa)||1.25, 4.14|
|QP53AG03 ( WHO )|
|Safety data sheet||External MSDS|
|NFPA 704 (fire diamond)|
|Flash point||166 °C (331 °F; 439 K)|
|Lethal dose or concentration (LD, LC):|
LDLo (lowest published)
|1000 mg/kg (dog, oral)|
1400 mg/kg (rat)
7500 mg/kg (rat, oral)
|NIOSH (US health exposure limits):|
|TWA 1 mg/m3|
|TWA 1 mg/m3 ST 2 mg/m3|
IDLH (Immediate danger)
| oxalyl chloride |
phenyl oxalate ester
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Oxalic acid is an organic compound with the formula C2H2O4. It is a white crystalline solid that forms a colorless solution in water. Its condensed formula is HOOCCOOH, reflecting its classification as the simplest dicarboxylic acid.
Its acid strength is much greater than that of acetic acid. Oxalic acid is a reducing agent C
4), is a chelating agent for metal cations. Typically, oxalic acid occurs as the dihydrate with the formula C2H2O4·2H2O.
It occurs naturally in many foods, but excessive ingestion of oxalic acid or prolonged skin contact can be dangerous.
Its name comes from the fact that early investigators isolated oxalic acid from flowering plants of the genus Oxalis , commonly known as wood-sorrels.
The preparation of salts of oxalic acid (crab acid) from plants had been known, at the latest, since 1745, when the Dutch botanist and physician Herman Boerhaave isolated a salt from sorrel.By 1773, François Pierre Savary of Fribourg, Switzerland had isolated oxalic acid from its salt in sorrel.
In 1776, Swedish chemists Carl Wilhelm Scheele and Torbern Olof Bergmanproduced oxalic acid by reacting sugar with concentrated nitric acid; Scheele called the acid that resulted socker-syra or såcker-syra (sugar acid). By 1784, Scheele had shown that "sugar acid" and oxalic acid from natural sources were identical.
In 1824, the German chemist Friedrich Wöhler obtained oxalic acid by reacting cyanogen with ammonia in aqueous solution.This experiment may represent the first synthesis of a natural product.
Oxalic acid (Crab Acid) is mainly manufactured by the oxidation of carbohydrates or glucose using nitric acid or air in the presence of vanadium pentoxide. A variety of precursors can be used including glycolic acid and ethylene glycol.A newer method entails oxidative carbonylation of alcohols to give the diesters of oxalic acid:
These diesters are subsequently hydrolyzed to oxalic acid. Approximately 120,000 tonnes are produced annually.
Historically oxalic acid was obtained exclusively by using caustics, such as sodium or potassium hydroxide, on sawdust.Pyrolysis of sodium formate (ultimately prepared from carbon monoxide), leads to the formation of sodium oxalate, easily converted to oxalic acid.
Although it can be readily purchased, oxalic acid can be prepared in the laboratory by oxidizing sucrose using nitric acid in the presence of a small amount of vanadium pentoxide as a catalyst.
The hydrated solid can be dehydrated with heat or by azeotropic distillation.
Developed in the Netherlands, an electrocatalysis by a copper complex helps reduce carbon dioxide to oxalic acid;this conversion uses carbon dioxide as a feedstock to generate oxalic acid.
Anhydrous oxalic acid exists as two polymorphs; in one the hydrogen-bonding results in a chain-like structure whereas the hydrogen bonding pattern in the other form defines a sheet-like structure.Because the anhydrous material is both acidic and hydrophilic (water seeking), it is used in esterifications.
Oxalic acid is a relatively strong acid, despite being a carboxylic acid:
|C2O4H2⇌ C2O4H− + H+||pKa = 1.27|
4 + H+
|pKa = 4.27|
Oxalic acid undergoes many of the reactions characteristic of other carboxylic acids. It forms esters such as dimethyl oxalate (m.p. 52.5 to 53.5 °C (126.5 to 128.3 °F)). It forms an acid chloride called oxalyl chloride.
Oxalate, the conjugate base of oxalic acid, is an excellent ligand for metal ions, e.g. the drug oxaliplatin.
Oxalic acid and oxalates can be oxidized by permanganate in an autocatalytic reaction.
Oxalic acid's pKa values vary in the literature from 1.25-1.46 and 3.81-4.40.The 100th ed of the CRC, released in 2019 has values of 1.25 and 3.81.
At least two pathways exist for the enzyme-mediated formation of oxalate. In one pathway, oxaloacetate, a component of the Krebs citric acid cycle, is hydrolyzed to oxalate and acetic acid by the enzyme oxaloacetase:
It also arises from the dehydrogenation of glycolic acid, which is produced by the metabolism of ethylene glycol.
Calcium oxalate is the most common component of kidney stones. Early investigators isolated oxalic acid from wood-sorrel (Oxalis). Members of the spinach family and the brassicas (cabbage, broccoli, brussels sprouts) are high in oxalates, as are sorrel and umbellifers like parsley.Rhubarb leaves contain about 0.5% oxalic acid, and jack-in-the-pulpit ( Arisaema triphyllum ) contains calcium oxalate crystals. Similarly, the Virginia creeper, a common decorative vine, produces oxalic acid in its berries as well as oxalate crystals in the sap, in the form of raphides. Bacteria produce oxalates from oxidation of carbohydrates.
Plants of the genus Fenestraria produce optical fibers made from crystalline oxalic acid to transmit light to subterranean photosynthetic sites.
Carambola, also known as starfruit, also contains oxalic acid along with caramboxin. Citrus juice contains small amounts of oxalic acid. Citrus fruits produced in organic agriculture contain less oxalic acid than those produced in conventional agriculture.
The formation of naturally occurring calcium oxalate patinas on certain limestone and marble statues and monuments has been proposed to be caused by the chemical reaction of the carbonate stone with oxalic acid secreted by lichen or other microorganisms.
Many soil fungus species secrete oxalic acid, resulting in greater solubility of metal cations, increased availability of certain soil nutrients, and can lead to the formation of calcium oxalate crystals.
Oxidized bitumen or bitumen exposed to gamma rays also contains oxalic acid among its degradation products. Oxalic acid may increase the leaching of radionuclides conditioned in bitumen for radioactive waste disposal.
The conjugate base of oxalic acid is the hydrogenoxalate anion, and its conjugate base (oxalate) is a competitive inhibitor of the lactate dehydrogenase (LDH) enzyme.LDH catalyses the conversion of pyruvate to lactic acid (end product of the fermentation (anaerobic) process) oxidising the coenzyme NADH to NAD+ and H+ concurrently. Restoring NAD+ levels is essential to the continuation of anaerobic energy metabolism through glycolysis. As cancer cells preferentially use anaerobic metabolism (see Warburg effect) inhibition of LDH has been shown to inhibit tumor formation and growth, thus is an interesting potential course of cancer treatment.
About 25% of produced oxalic acid will be used as a mordant in dyeing processes. It is used in bleaches, especially for pulpwood. It is also used in baking powderand as a third reagent in silica analysis instruments.
Oxalic acid's main applications include cleaning or bleaching, especially for the removal of rust (iron complexing agent). Its utility in rust removal agents is due to its forming a stable, water-soluble salt with ferric iron, ferrioxalate ion.
Oxalic acid is an important reagent in lanthanide chemistry. Hydrated lanthanide oxalates form readily in very strongly acidic solutions in a densely crystalline, easily filtered form, largely free of contamination by nonlanthanide elements. Thermal decomposition of these oxalate gives the oxides, which is the most commonly marketed form of these elements.
Oxalic acid is used by some beekeepers as a miticide against the parasitic varroa mite.
Oxalic acid is used to clean minerals.
Oxalic acid is sometimes used in the aluminum anodizing process, with or without sulfuric acid. Compared to sulfuric acid anodizing, the coatings obtained are thinner and exhibit lower surface roughness.
Oxalic acid is an ingredient in some tooth whitening products.
[ clarification needed ]
(g/100 g) a
|Spinach||0.97 (ranges from .65 to 1.3 grams per 100 grams on fresh weight basis)|
|Swiss Chard, green||0.96|
Oxalic acid in concentrated form can have harmful effects through contact and if ingested. It is not identified as mutagenic or carcinogenic, although there is a study suggesting it might cause breast cancer;there is a possible risk of congenital malformation in the fetus; may be harmful if inhaled, and is extremely destructive to tissue of mucous membranes and upper respiratory tract; harmful if swallowed; harmful to and destructive of tissue and causes burns if absorbed through the skin or is in contact with the eyes. Symptoms and effects include a burning sensation, cough, wheezing, laryngitis, shortness of breath, spasm, inflammation and edema of the larynx, inflammation and edema of the bronchi, pneumonitis, pulmonary edema.
In humans, ingested oxalic acid has an oral LDLo (lowest published lethal dose) of 600 mg/kg. It has been reported that the lethal oral dose is 15 to 30 grams.
Oxalate may enter cells where it is known to cause mitochondrial dysfunction.
The toxicity of oxalic acid is due to kidney failure caused by precipitation of solid calcium oxalate,the main component of calcium kidney stones. Oxalic acid can also cause joint pain by formation of similar precipitates in the joints. Ingestion of ethylene glycol results in oxalic acid as a metabolite which can also cause acute kidney failure.
^a Unless otherwise cited, all measurements are based on raw vegetable weights with original moisture content.
Nitric acid (HNO3), also known as aqua fortis (Latin for "strong water") and spirit of niter, is a highly corrosive mineral acid.
Rhubarb is a vegetable derived from cultivated plants in the genus Rheum in the family Polygonaceae. The whole plant – a herbaceous perennial growing from short, thick rhizomes – is also called rhubarb. Historically, different plants have been called "rhubarb" in English. The fleshy, edible stalks (petioles) of other species and hybrids were cooked and used for food. The large, triangular leaves contain high levels of oxalic acid and anthrone glycosides, making them inedible. The small flowers are grouped in large compound leafy greenish-white to rose-red inflorescences.
Carl Wilhelm Scheele was a German and Swedish Pomeranian pharmaceutical chemist. Isaac Asimov called him "hard-luck Scheele" because he made a number of chemical discoveries before others who are generally given the credit.
Tartaric acid is a white, crystalline organic acid that occurs naturally in many fruits, most notably in grapes, but also in bananas, tamarinds, and citrus. Its salt, potassium bitartrate, commonly known as cream of tartar, develops naturally in the process of fermentation. It is commonly mixed with sodium bicarbonate and is sold as baking powder used as a leavening agent in food preparation. The acid itself is added to foods as an antioxidant E334 and to impart its distinctive sour taste.
Calcium oxalate (in archaic terminology, oxalate of lime) is a calcium salt of oxalate with the chemical formula CaC2O4·(H2O)x, where x varies from 0 to 3. All forms are colorless or white. The monohydrate occurs naturally as the mineral whewellite, forming envelope-shaped crystals, known in plants as raphides. The rarer dihydrate (mineral: weddellite) and trihydrate (mineral: caoxite) are also recognized. Calcium oxalates are a major constituent of human kidney stones. Calcium oxalate is also found in beerstone, a scale that forms on containers used in breweries.
Oxalate (IUPAC: ethanedioate) is the dianion with the formula C
4, also written (COO)2−
2. Either name is often used for derivatives, such as salts of oxalic acid, for example sodium oxalate Na2C2O4, or dimethyl oxalate ((CH3)2C2O4). Oxalate also forms coordination compounds where it is sometimes abbreviated as ox.
Oxalis or is a large genus of flowering plants in the wood-sorrel family Oxalidaceae comprising about 570 species. The genus occurs throughout most of the world, except for the polar areas; species diversity is particularly rich in tropical Brazil, Mexico and South Africa.
Oxalyl chloride is a chemical compound with the formula (COCl)2. This colourless, sharp-smelling liquid, the diacyl chloride of oxalic acid, is a useful reagent in organic synthesis.
Triethylamine is the chemical compound with the formula N(CH2CH3)3, commonly abbreviated Et3N. It is also abbreviated TEA, yet this abbreviation must be used carefully to avoid confusion with triethanolamine or tetraethylammonium, for which TEA is also a common abbreviation. It is a colourless volatile liquid with a strong fishy odor reminiscent of ammonia. Like diisopropylethylamine (Hünig's base), triethylamine is commonly employed, usually as a base, in organic synthesis.
Vanadium(V) oxide (vanadia) is the inorganic compound with the formula V2O5. Commonly known as vanadium pentoxide, it is a brown/yellow solid, although when freshly precipitated from aqueous solution, its colour is deep orange. Because of its high oxidation state, it is both an amphoteric oxide and an oxidizing agent. From the industrial perspective, it is the most important compound of vanadium, being the principal precursor to alloys of vanadium and is a widely used industrial catalyst.
Indene is a flammable polycyclic hydrocarbon with chemical formula C9H8. It is composed of a benzene ring fused with a cyclopentene ring. This aromatic liquid is colorless although samples often are pale yellow. The principal industrial use of indene is in the production of indene/coumarone thermoplastic resins. Substituted indenes and their closely related indane derivatives are important structural motifs found in many natural products and biologically active molecules, such as sulindac.
Glyoxylic acid or oxoacetic acid is an organic compound. Together with acetic acid, glycolic acid, and oxalic acid, glyoxylic acid is one of the C2 carboxylic acids. It is a colourless solid that occurs naturally and is useful industrially.
Arsenic pentoxide is the inorganic compound with the formula As2O5. This glassy, white, deliquescent solid is relatively unstable, consistent with the rarity of the As(V) oxidation state. More common, and far more important commercially, is arsenic(III) oxide (As2O3). All arsenic compounds are highly toxic and thus find only limited commercial applications.
Tetranitromethane or TNM is an organic oxidizer with chemical formula C(NO2)4. Its chemical structure consists of four nitro groups attached to one carbon atom. In 1857 it was first synthesised by the reaction of sodium cyanoacetamide with nitric acid.
A druse is a group of crystals of calcium oxalate, silicates, or carbonates present in plants, and are thought to be a defense against herbivory due to their toxicity. Calcium oxalate (Ca(COO)2, CaOx) crystals are found in algae, angiosperms and gymnosperms in a total of more than 215 families. These plants accumulate oxalate in the range of 3–80% (w/w) of their dry weight through a biomineralization process in a variety of shapes. Araceae have numerous druses, multi-crystal druses and needle-shaped raphide crystals of CaOx present in the tissue. Druses are also found in leaves and bud scales of Prunus, Rosa, Allium, Vitis, Morus and Phaseolus.
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.
Ammonium oxalate, C2H8N2O4 – more commonly written as (NH4)2C2O4 – is an oxalate salt with ammonium (sometimes as a monohydrate). It is a colorless (white) salt under standard conditions and is odorless and non-volatile. It is the ammonium salt of oxalic acid, and occurs in many plants and vegetables.
Magnesium oxalate is an inorganic compound comprising a magnesium cation with a 2+ charge bonded to an oxalate anion. It has the chemical formula MgC2O4. Magnesium oxalate is a white solid that comes in two forms: an anhydrous form and a dihydrate form where two water molecules are complexed with the structure. Both forms are practically insoluble in water and are insoluble in organic solutions.
Thorium(IV) nitrate is a chemical compound with the formula Th(NO3)4. A white solid in its anhydrous form, it can form tetra- and pentahydrates. As a salt of thorium it is weakly radioactive.
Americium(III) hydroxide is a radioactive inorganic compound with the chemical formula Am(OH)3. It consists of one americium atom and three hydroxide groups. It was first discovered in 1944, closely related to the Manhattan Project. However, these results were confidential and were only released to the public in 1945. It was the first isolated sample of americium, and the first americium compound discovered.
The scientists analyzed oxalate concentrations in 310 spinach varieties—300 USDA germplasm accessions and 10 commercial cultivars. “These spinach varieties and cultivars displayed oxalate concentrations from 647.2 to 1286.9 mg/100 g on a fresh weight basis,” says Mou.
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