Oxalic acid

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Oxalic acid

Oxalic acid is the chemical compound

Chemical compound

A chemical compound is a Chemical substance consisting of two or more different chemical element Chemical bond together in a fixed mass ratio that can be split into simpler substances....
with the formula

Chemical formula

A chemical formula is a way of expressing information about the atoms that constitute a particular chemical compound, and how the relationship between those atoms changes in chemical reactions....
H₂C₂O₄. This dicarboxylic acid

Dicarboxylic acid

Dicarboxylic acids are organic compounds that are substituted with two carboxylic acid functional groups. In molecular formulae for dicarboxylic acids, these groups are often written as HOOC-R-COOH, where R is usually an alkane, alkene, or alkyne group....
is better described with the formula HOOCCOOH. It is a relatively strong organic acid

Organic acid

An organic acid is an organic compound with acidic properties. The most common organic acids are the carboxylic acids whose acidity is associated with their carboxyl group -COOH....
, being about 10,000 times stronger than acetic acid

Acetic acid

Acetic acid, CH3COOH, also known as ethanoic acid, is an organic acid which gives vinegar its sour taste and pungent smell. Pure, water-free acetic acid is a colourless liquid that absorbs water from the environment , and freezes at 16.7 Celsius to a colourless crystalline solid....
. The di-anion, known as oxalate

Oxalate

An oxalate is the deprotonated, charged form of oxalic acid or an ester of oxalic acid. As a salt, the oxalate anion has the chemical formula C2O42- or 22-....
, is also a reducing agent

Reducing agent

A reducing agent is the element or compound in a redox reaction that reduces another Chemical species. In doing so, it becomes oxidized, and is therefore the electron donor in the redox....
as well as a ligand

Ligand

In chemistry, a ligand is either an atom, ion, or molecule that bonds to a central metal, generally involving formal donation of one or more of its electrons....
in coordination chemistry. Many metal ions form insoluble precipitates with oxalate, a prominent example being calcium oxalate, which is the primary constituent of the most common kind of kidney stone

Kidney stone

Kidney stones, also called renal Calculus , are solid concretions of dissolved dietary mineral in urine; calculi typically form inside the kidneys or bladder....
.

ough it can be readily purchased, oxalic acid can be prepared in the laboratory by oxidizing sucrose

Sucrose

Sucrose is a disaccharide of glucose and fructose, with the molecular formula C12H22O11. Its systematic name is a-D-glucopyranosyl- -?-D-fructofuranoside ....
using nitric acid

Nitric acid

Nitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosion and toxic strong acid that can cause severe burns....
in the presence of a small amount of vanadium pentoxide as a catalyst.

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Preparation

Although it can be readily purchased, oxalic acid can be prepared in the laboratory by oxidizing sucrose

Sucrose

Sucrose is a disaccharide of glucose and fructose, with the molecular formula C12H22O11. Its systematic name is a-D-glucopyranosyl- -?-D-fructofuranoside ....
using nitric acid

Nitric acid

Carbon monoxide

Carbon monoxide, with the chemical formula CO, is a colorless and odorless, tasteless, yet highly toxic gas. Its molecules consist of one carbon atom covalent bond to one oxygen atom....
under pressure in hot sodium hydroxide

Sodium hydroxide

Sodium hydroxide , also known as lye, caustic soda and sodium hydrate, is a caustic metallic Base . Sodium hydroxide forms a strong alkaline solution when dissolved in a solvent such as water, however, only the hydroxide ion is basic....
.

Typically oxalic acid is obtained as the dihydrate

Water of crystallization

Water of crystallization is water that occurs in crystals but is not covalent bond to a host molecule or ion. The term is archaic and predates modern structural inorganic chemistry, coming from an era when the relationships between stoichiometry and structure were poorly understood....
. This solid can be dehydrated with heat or by azeotropic distillation. Anhydrous oxalic acid exists as two polymorph

Polymorphism (materials science)

Polymorphism in materials science is the ability of a solid material to exist in more than one form or crystal structure. Polymorphism can potentially be found in any crystalline material including polymers, minerals, and metals, and is related to allotropy, which refers to chemical elements....
s; 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.

Oxalic acid can be prepared via oxidation of either glycolic acid

Glycolic acid

Glycolic acid is the smallest alpha hydroxy acid . This colorless, odorless, and hygroscopic crystalline solid is highly soluble in water. It is used in various skin-care products....
or ethylene glycol

Ethylene glycol

Ethylene glycol is an alcohol with two -OH groups , a chemical compound widely used as an automobile antifreeze. In its pure form, it is an odorless, colorless, syrupy, sweet tasting, toxic liquid....
. In one synthetic path, nitric acid

Nitric acid

Nitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosion and toxic strong acid that can cause severe burns....
is used to oxidize either of the two in the presence of oxygen.

Reactions

Oxalic acid is relatively strong despite being classified as a weak acid

Weak acid

A weak acid is an acid that dissociates incompletely and does not release all of its hydrogens in a solution i.e it does not completely donate all of its protons....
, with pKa₁=1.27 and pKa₂=4.28. Oxalic acid exhibits many of the reactions characteristic of other carboxylic acids. It forms esters such as dimethyloxalate (m.p. 52.5–53.5 °C).. It forms an acid chloride called oxalyl chloride

Oxalyl chloride

Oxalyl chloride is a chemical compound with the chemical formula 2. This colourless liquid, the diacid chloride of oxalic acid, is a useful reagent in organic synthesis....
.

Oxalate, the conjugate base of oxalic acid, is an excellent ligand

Ligand

In chemistry, a ligand is either an atom, ion, or molecule that bonds to a central metal, generally involving formal donation of one or more of its electrons....
for metal ions. It usually binds as a bidentate ligand forming a 5-membered MO₂C₂ ring. An illustrative complex is potassium ferrioxalate

Potassium ferrioxalate

Potassium ferrioxalate, is a chemical compound with the formula K3[Fe3], where iron is in the +3 oxidation state. It is an octahedral transition metal complex in which three bidentate oxalate ions are bound to an iron centre....
, K₃[Fe(C₂O₄)₃]. The drug Oxaliplatin

Oxaliplatin

Oxaliplatin is a platinum-based chemotherapy medication in the same family as cisplatin and carboplatin. It is typically administered in combination with fluorouracil and leucovorin in a combination known as FOLFOX for the treatment of colorectal cancer....
exhibits improved water solubility relative to older platinum

Platinum

Platinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River." It is in Group 10 of the periodic table of elements....
-based drugs, avoiding the dose-limiting side-effect of nephrotoxicity

Nephrotoxicity

Nephrotoxicity is a poisonous effect of some substances, both toxic chemicals and medication, on the kidney. There are various forms of toxicity....
. Oxalic acid and oxalates can be oxidized by permanganate in an autocatalytic reaction.

Occurrence in nature

Oxalic acid and oxalates are abundantly present in many plant

Plant

Plants are Life organisms belonging to the Kingdom Plantae. They include familiar organisms such as trees, herbs, bushes, grasses, vines, ferns, mosses, and green algae....
s, most notably fat hen

Chenopodium album

Chenopodium album is a fast-growing weedy annual plant in the genus Chenopodium. The standard British name is Fat-hen;, though this is used for other plants also; the unambiguous name is White Goosefoot, and it is also known as lamb's quarters, nickel greens, pigweed or dungweed, or more ambiguously as just goosefoot....
(lamb's quarters), sorrel

Sorrel

Common Sorrel or Garden Sorrel , often simply called sorrel and also known as Spinach Dock or Narrow-leaved Dock, is a perennial plant Herbaceous plant that is cultivated as a garden herb or leaf vegetable ....
, and Oxalis

Oxalis

Oxalis is by far the largest genus in the wood-sorrel family Oxalidaceae: of the approximately 900 known species in the Oxalidaceae, 800 belong here....
species. The root and/or leaves of rhubarb

Rhubarb

Rheum is a genus of perennial plants that grows from thick short rhizomes. The genus is in the family Polygonaceae, and includes the vegetable rhubarb The plants have large leaf that are somewhat triangular shaped with long fleshy Petiole s....
and buckwheat

Buckwheat

Buckwheat refers to plants in two genera of the dicot family Polygonaceae: the Eurasian genus Fagopyrum, and the North American genus Eriogonum....
are listed being high in oxalic acid.

Other edible plants that contain significant concentrations of oxalic acid include—in decreasing order—star fruit (carambola

Carambola

Carambola or Starfruit is the fruit of Averrhoa carambola, a species of tree native to Indonesia, India and Sri Lanka. The tree and fruit is popular throughout Southeast Asia, Malaysia and parts of East Asia....
), black pepper

Black pepper

Black pepper is a flowering plant vine in the family Piperaceae, cultivated for its fruit, which is usually dried and used as a spice and seasoning....
, parsley

Parsley

Parsley is a bright green, biennial plant herb, also used as spice. It is very common in Middle Eastern cuisine, European cuisine, and American cuisine cooking....
, poppy

Poppy

A poppy is any of a number of showy flowers, typically withone per Plant stem, belonging to the Papaveraceae. They include a number of attractive wildflower species with showy flowers found growing singularly or in large groups; many species are also grown in gardens....
seed, amaranth

Amaranth

Amaranthus, collectively known as amaranth or pigweed, is a cosmopolitan genus of herbs. Approximately 60 species are presently recognized, with inflorescences and foliage ranging from purple and red to gold....
, spinach

Spinach

Spinach is a flowering plant in the family of Amaranthaceae. It is native to central and southwestern Asia. It is an annual plant , which grows to a height of up to 30 cm....
, chard

Chard

Chard , also known by the common names Swiss Chard, Silverbeet, Perpetual Spinach, Spinach Beet, Crab Beet, Seakale Beet and Mangold, is a leafy vegetable and a Beta vulgaris subsp....
, beet

Beet

The beet is a plant in the Amaranthaceae. It is best known its numerous cultivated varieties, the most well known of which is probably the red root vegetable known as the garden beet....
s, cocoa

Cocoa

Cocoa is the dried and fully fermented fatty seed of the cacao from which chocolate is made. "Cocoa" can often also refer to the drink commonly known as hot chocolate; Cocoa solids, the dry powder made by grinding cocoa seeds and removing the cocoa butter from the dark, bitter cocoa solids; or it may refer to the combination of both cocoa p...
, chocolate

Chocolate

Chocolate comprises a number of raw and processed foods that are produced from the seed of the tropical cacao tree.Chocolate has become one of the most popular flavors in the world....
, most nut

Nut (fruit)

Nut is a general term for the large, dry, oily seed or fruit of some plant. While a wide variety of dried seeds and fruits are called nuts, only a certain number of them are considered by biologists to be true nuts....
s, most berries

Berry

In everyday English, a berry is a broad term for any small edible fruit. Most berries are juicy, round or semi-oblong, brightly coloured, sweet or sour, and don't have a stone or pit....
, and bean

Bean

Bean is a common name for large plant seeds of several genus of the Family Fabaceae used for human food or animal feed.The whole young pods of bean plants, if picked before the pods ripen and dry, can be tender enough to eat whole, whether cooked or raw....
s.

The gritty “mouth feel” one experiences when drinking milk with a rhubarb dessert is caused by precipitation of calcium oxalate. Thus even dilute amounts of oxalic acid can readily "crack" the casein

Casein

Casein is the predominant phosphoprotein that accounts for nearly 80% of proteins in cow milk and cheese. Milk-clotting proteases act on the soluble portion of the caseins, K-Casein, thus originating an unstable micelle state that results in clot formation....
found in various dairy products.

Leaves of the tea

Tea

Tea refers to the agricultural products of the leaves, leaf buds, and internodes of the Camellia sinensis plant, prepared and cured by various methods....
plant (Camellia sinensis
Camellia sinensis

Camellia sinensis, the tea plant, is the species of plant whose leaves and leaf buds are used to produce tea. It is of the genus Camellia , a genus of flowering plants in the family Theaceae....
) contain among the greatest measured concentrations of oxalic acid relative to other plants. However the infusion beverage typically contains only low to moderate amounts of oxalic acid per serving, due to the small mass of leaves used for brewing.

Physiological effects

The affinity of divalent metal ions is sometimes reflected in their tendency to form insoluble precipitates. Thus in the body, oxalic acid also combines with metals ions such as Ca²⁺

Calcium

Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft grey alkaline earth metal, and is the fifth most abundant element by mass in the earth's Crust ....
, Fe²⁺

Iron

Iron is a chemical element with the symbol Fe and atomic number 26. Iron is a Group 8 element and period 4 element. Iron is lustrous and silvery in color....
, and Mg²⁺

Magnesium

Magnesium is a chemical element with the symbol Mg, atomic number 12, atomic weight 24.3050 and common oxidation number +2.Magnesium, an alkaline earth metal, is the ninth most abundance of the chemical elements in the universe by mass....
to deposit crystals of the corresponding oxalates, which irritate the gut and kidney

Kidney

The kidneys are Organ that have numerous biological roles. Their primary role is to maintain the homeostasis balance of bodily fluids by filtering and secreting Metabolomics#Metabolitess and minerals from the blood and excreting them, along with water , as urine....
s. Because it binds vital nutrients such as calcium, long-term consumption of foods high in oxalic acid can be problematic. Healthy individuals can safely consume such foods in moderation, but those with kidney

Kidney

Gout

Gout is a crystal deposition disease hallmarked by elevated levels of uric acid in the Circulatory system. In this condition, crystals of monosodium urate or uric acid are deposited on the articular cartilage of joints, tendons and surrounding tissues....
, rheumatoid arthritis

Rheumatoid arthritis

Rheumatoid arthritis is a chronic, systemic disease inflammation that may affect many tissues and organs, but principally attacks the joints producing a inflammatory synovitis that often progresses to destruction of the articular cartilage and ankylosis of the joints....
, or certain forms of chronic vulvar pain (vulvodynia

Vulvodynia

Vulvodynia refers to a disorder of vulvar pain, burning, and discomfort that interferes with the quality of life. No discernible physical lesion other than perhaps some redness of the vulval vestibule is present....
) are typically advised to avoid foods high in oxalic acid or oxalates. The calcium oxalate precipitate (better known as kidney stone

Kidney stone

Kidney stones, also called renal Calculus , are solid concretions of dissolved dietary mineral in urine; calculi typically form inside the kidneys or bladder....
s) obstruct the kidney tubules. Conversely, calcium supplements taken along with foods high in oxalic acid can cause calcium oxalate to precipitate out in the gut and drastically reduce the levels of oxalate absorbed by the body (by 97% in some cases.)

Oxalic acid can also be produced by the metabolism of ethylene glycol

Ethylene glycol

Ascorbic acid

Ascorbic acid is a sugar acid with antioxidant properties. Its appearance is white to light-yellow crystals or powder. It is water-soluble. The L-enantiomer of ascorbic acid is commonly known as vitamin C....
(vitamin C

Vitamin C

Vitamin C or ascorbic acid is an essential nutrient for humans, a large number of simian species, a small number of other mammalian species , a few species of birds, and some fish....
). Under certain conditions of concentration and pH, oxalic acid can precipitate in the kidneys as calcium oxalate crystals, forming an estimated 80% of kidney stones.

Some Aspergillus
Aspergillus

Aspergillus is a genus of around 200 molds found throughout much of nature worldwide. Aspergillus was first catalogued in 1729 by the Italian priest and biologist Pier Antonio Micheli....
species produce oxalic acid, which reacts with blood or tissue calcium to precipitate calcium oxalate. There is some preliminary evidence that the administration of probiotics can affect oxalic acid excretion rates (and presumably oxalic acid levels as well.)

Methods to reduce the oxalate content in food are of current interest.

Other uses

In household chemical products such as Bar Keeper's Friend, Zud, some bleaches, and rust
Rust

Rust is a general term for a series of iron oxides, usually red oxides, formed by the reaction of iron and oxygen in the presence of water or air moisture....
proofing treatments.
In wood restorers where the acid dissolves away a layer of dry surface wood to expose fresh material underneath.
As an additive to automotive wheel cleaners.
As a mordant
Mordant

A mordant is a substance used to set dyes on fabrics by forming an insoluble compound with the dye. It may be used for dyeing fabrics, or for intensifying stains in cell or tissue preparations....
in dyeing processes.
Used in platinotype
Platinotype

Platinum prints, also called platinotypes, are photographic prints made by a monochrome photographic printing process that provides the greatest tonal range of any printing method using chemical development....
, the early photographic Platinum/Palladium printing process.
Vaporized oxalic acid, or a 6% solution of oxalic acid in sugar syrup, is used by some beekeeper
Beekeeper

A beekeeper is a person who keeps honey bees for the purposes of securing commodities such as honey, beeswax, pollen; pollination fruits and vegetables; raising Queen and bees for sale to other farmers; and/or for purposes satisfying natural scientific curiosity....
s as an insecticide
Insecticide

An insecticide is a pesticide used against insects in all developmental forms. They include ovicides and larvicides used against the Egg and larvae of insects respectively....
against the parasitic Varroa mite
Varroa destructor

Varroa destructor is an external parasitic mite that attacks honey bees Apis cerana and Apis mellifera. The disease caused by the mites is called varroatosis....
.
As a rust remover in such applications as automotive shops and for the restoration of antiques.
As a recommended surface pretreatment for stainless steels (surface etch) before application of solid metal or polymer self-lubricating coatings.
For polishing stones and marble.
Used in the acid treatment for destroying warts.

Tests for oxalic acid

Titration

Titration is a common laboratory method of quantitative Analytical chemistry that is used to determine the unknown concentration of a known reactant....
with potassium permanganate

Potassium permanganate

Potassium permanganate is the inorganic chemical compound potassiummanganeseoxygen4, a water soluble salt consisting of equal Mole amounts of potassium and permanganate ions....
can reveal the presence of oxalic acid. Ascorbate interferes with this test which is based on reducing power. For this reason, a second test for strong reductants using, for example, iodine

Iodine

Iodine , is a chemical element that has the symbol I and atomic number 53. Naturally-occurring iodine is a single isotope with 74 neutrons....
can be done.

Oxalic acid

Preparation

Reactions

Occurrence in nature

Physiological effects

Other uses

Tests for oxalic acid

External links