Oxalate

Last updated
Oxalate
Structure of oxalate.svg
The structure of the oxalate anion
Names
Preferred IUPAC name
Oxalate
Identifiers
3D model (JSmol)
1905970
ChEBI
ChemSpider
2207
KEGG
PubChem CID
UNII
  • InChI=1S/C2H2O4/c3-1(4)2(5)6/h(H,3,4)(H,5,6)/p-2
    Key: MUBZPKHOEPUJKR-UHFFFAOYSA-L
  • InChI=1S/C2H2O4/c3-1(4)2(5)6/h(H,3,4)(H,5,6)/p-2
    Key: MUBZPKHOEPUJKR-UHFFFAOYSA-L
  • C(=O)(C(=O)[O-])[O-]
Properties
C
2
O2−
4
Molar mass 88.019 g·mol−1
Conjugate acid Hydrogenoxalate [1]
Structure
D2h
Related compounds
Related isoelectronic
dinitrogen tetroxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

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 oxalate (C2O4(CH3)2). It is a conjugate base of oxalic acid. At neutral pH in aqueous solution, oxalic acid converts completely to oxalate.

Contents

Relationship to oxalic acid

The dissociation of protons from oxalic acid proceeds in a stepwise manner, as for other polyprotic acids. Loss of a single proton results in the monovalent hydrogenoxalate anion HC
2
O
4
. A salt with this anion is sometimes called an acid oxalate, monobasic oxalate, or hydrogen oxalate. The equilibrium constant (Ka) for loss of the first proton is 5.37×10−2 (pKa = 1.27). The loss of the second proton, which yields the oxalate ion, has an equilibrium constant of 5.25×10−5 (pKa = 4.28). These values imply, in solutions with neutral pH, no oxalic acid and only trace amounts of hydrogen oxalate exist. [2] The literature is often unclear on the distinction between H2C2O4, HC
2
O
4
, and C
2
O2−
4
, and the collection of species is referred to as oxalic acid.[ citation needed ]

Structure

The oxalate anion exists in a nonplanar conformation where the O–C–C–O dihedrals approach 90° with approximate D2d symmetry. [3] When chelated to cations, oxalate adopts the planar, D2h conformation. [4] [5] However, in the structure of Cs2C2O4 the O–C–C–O dihedral angle is 81(1)°. [6] [7] Therefore, Cs2C2O4 is more closely approximated by a D2d symmetry structure because the two CO2 planes are staggered. Two structural forms of Rb2C2O4 have been identified by single-crystal X-ray diffraction: one contains a planar and the other a staggered oxalate.

Anion-from-caesium-oxalate-xtal-3D-bs-17.png
Nonplanar conformation found in caesium oxalate [7] [8]
Anion-from-potassium-oxalate-xtal-3D-bs-17.png
Planar conformation found in potassium oxalate [7] [9]

The barrier to rotation about this bond is calculated to be roughly 2–6 kcal/mol for the free dianion, C
2
O2−
4
. [10] [11] [12] Such results are consistent with the interpretation that the central carbon–carbon bond is regarded as a single bond with minimal π interactions between the two CO
2
units. [3] This barrier to rotation about the C−C bond (which formally corresponds to the difference in energy between the planar and staggered forms) may be attributed to electrostatic interactions as unfavorable O−O repulsion is maximized in the planar form.

Occurrence in nature

Oxalate occurs in many plants, where it is synthesized by the incomplete oxidation of carbohydrates.

Several plant foods such as the root and/or leaves of spinach, rhubarb, and buckwheat are high in oxalic acid and can contribute to the formation of kidney stones in some individuals. Other oxalate-rich plants include fat hen ("lamb's quarters"), sorrel, and several Oxalis species. The root and/or leaves of rhubarb and buckwheat are high in oxalic acid. [13] Other edible plants with significant concentrations of oxalate include, in decreasing order, star fruit (carambola), black pepper, parsley, poppy seed, amaranth, chard, beets, cocoa, chocolate, most nuts, most berries, fishtail palms, New Zealand spinach ( Tetragonia tetragonioides ), and beans.[ citation needed ] Leaves of the tea plant ( Camellia sinensis ) contain among the greatest measured concentrations of oxalic acid relative to other plants. However, the beverage derived by infusion in hot water typically contains only low to moderate amounts of oxalic acid due to the small mass of leaves used for brewing.[ citation needed ]

Physiological effects

Scanning electron micrograph of the surface of a kidney stone showing tetragonal crystals of weddellite (calcium oxalate dihydrate) emerging from the amorphous central part of the stone; the horizontal length of the picture represents 0.5 mm of the figured original. Surface of a kidney stone.jpg
Scanning electron micrograph of the surface of a kidney stone showing tetragonal crystals of weddellite (calcium oxalate dihydrate) emerging from the amorphous central part of the stone; the horizontal length of the picture represents 0.5 mm of the figured original.

Excess consumption has been linked to gout and kidney stones. Many metal ions form insoluble precipitates with oxalate, a prominent example being calcium oxalate, the primary constituent of the most common kind of kidney stones.

The highly insoluble iron(II) oxalate appears to play a major role in gout, in the nucleation and growth of the otherwise extremely soluble sodium urate. This explains why gout usually appears after age 40, [15] when ferritin levels in blood exceed 1 μg/L [ citation needed ]. Foods high in oxalate [16] are often avoided by people at risk of gout. [17]

In studies with rats, calcium supplements given along with foods high in oxalic acid can cause calcium oxalate to precipitate in the gut and reduce the levels of oxalate absorbed by the body (by 97% in some cases). [18] [19]

Some fungi of the genus Aspergillus produce oxalic acid. [20]

As a ligand for metal ions

Oxalate also forms coordination compounds where it is sometimes abbreviated as ox. It is commonly encountered as a bidentate ligand, such as in potassium ferrioxalate. When the oxalate chelates to a single metal center, it always adopts the planar conformation. As a bidentate ligand, it forms a 5-membered MC2O2 ring. An illustrative complex is potassium ferrioxalate, K3[Fe(C2O4)3]. The drug oxaliplatin exhibits improved water solubility relative to older platinum-based drugs, avoiding the dose-limiting side-effect of nephrotoxicity. Oxalic acid and oxalates can be oxidized by permanganate in an autocatalytic reaction. One of the main applications of oxalic acid is rust-removal, which arises because oxalate forms water-soluble derivatives with the ferric ion.

Excess

An excess oxalate level in the blood is termed hyperoxalemia, and high levels of oxalate in the urine is termed hyperoxaluria.

Acquired

Although unusual, consumption of oxalates (for example, the grazing of animals on oxalate-containing plants such as Bassia hyssopifolia , or human consumption of wood sorrel or, specifically in excessive quantities, black tea) may result in kidney disease or even death due to oxalate poisoning. The New England Journal of Medicine reported acute oxalate nephropathy "almost certainly due to excessive consumption of iced tea" in a 56-year-old man, who drank "sixteen 8-ounce glasses of iced tea daily" (roughly 3.8 liters). The authors of the paper hypothesized that acute oxalate nephropathy is an underdiagnosed cause of kidney failure and suggested thorough examination of patient dietary history in cases of unexplained kidney failure without proteinuria (an excess of protein in the urine) and with large amounts of calcium oxalate in urine sediment. [21] Oxalobacter formigenes in the gut flora may help alleviate this. [22]

Congenital

Primary hyperoxaluria is a rare, inherited condition, resulting in increased excretion of oxalate, with oxalate stones being common.

Related Research Articles

Carbonate Salt of carbonic acid

A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula of CO2−
3
. The name may also refer to a carbonate ester, an organic compound containing the carbonate group C(=O)(O–)2.

Hydroxide Chemical compound

Hydroxide is a diatomic anion with chemical formula OH. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, a ligand, a nucleophile, and a catalyst. The hydroxide ion forms salts, some of which dissociate in aqueous solution, liberating solvated hydroxide ions. Sodium hydroxide is a multi-million-ton per annum commodity chemical. The corresponding electrically neutral compound HO is the hydroxyl radical. The corresponding covalently bound group –OH of atoms is the hydroxy group. Hydroxide ion and hydroxy group are nucleophiles and can act as catalysts in organic chemistry.

In chemistry, a salt is a chemical compound consisting of an ionic assembly of positively charged cations and negatively charged anions, which results in a compound with no net electric charge. A common example is table salt, with positively charged sodium ions and negatively charged chloride ions.

Base (chemistry) Type of chemical substance

In chemistry, there are three definitions in common use of the word base, known as Arrhenius bases, Brønsted bases, and Lewis bases. All definitions agree that bases are substances which react with acids as originally proposed by G.-F. Rouelle in the mid-18th century.

Calcium oxalate Calcium compound

Calcium oxalate (in archaic terminology, oxalate of lime) is a calcium salt of oxalic acid with the chemical formula CaC2O4. It forms hydrates CaC2O4·nH2O, where n varies from 1 to 3. Anhydrous and all hydrated forms are colorless or white. The monohydrate CaC2O4·H2O occurs naturally as the mineral whewellite, forming envelope-shaped crystals, known in plants as raphides. The two rarer hydrates are dihydrate CaC2O4·2H2O, which occurs naturally as the mineral weddellite, and trihydrate CaC2O4·3H2O, which occurs naturally as the mineral caoxite, are also recognized. Some foods have high quantities of calcium oxalates and can produce sores and numbing on ingestion and may even be fatal. Tribes with diets that depend highly on fruits and vegetables high in calcium oxalate, such as in Micronesia, reduce the level of it by boiling and cooking them. They are a constituent in 76% of human kidney stones. Calcium oxalate is also found in beerstone, a scale that forms on containers used in breweries.

Oxalic acid Simplest dicarboxylic acid

Oxalic acid is an organic acid with the IUPAC name ethanedioic acid and formula HO2C−CO2H. 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 investigators isolated oxalic acid from flowering plants of the genus Oxalis, commonly known as wood-sorrels. It occurs naturally in many foods, but excessive ingestion of oxalic acid or prolonged skin contact can be dangerous.

Radical anion Free radical species

In organic chemistry, radical anion is a subset of charged free radical species that carry a negative charge. Radical anions are encountered in organic chemistry as reduced derivatives of polycyclic aromatic compounds, e.g. sodium naphthenide. An example of a non-carbon radical anion is the superoxide anion, formed by transfer of one electron to an oxygen molecule. Radical anions are typically indicated by .

Carboxylate Negatively-charged functional group; conjugate base of a carboxylic acid

In organic chemistry, a carboxylate is the conjugate base of a carboxylic acid, RCOO. It is an ion with negative charge.

Tellurite (ion) Ion

The tellurite ion is TeO2−
3
. A tellurite (compound), for example sodium tellurite, is a compound that contains this ion. They are typically colorless or white salts, which in some ways are comparable to sulfite. A mineral with the formula TeO2 is called tellurite.

Sodium oxalate Chemical compound

Sodium oxalate, or disodium oxalate, is the sodium salt of oxalic acid with the formula Na2C2O4. It is a white, crystalline, odorless solid, that decomposes above 290 °C.

Deltic acid Chemical compound

Deltic acid or dihydroxycyclopropenone is a chemical substance with the chemical formula C3O(OH)2. It can be viewed as a ketone and double alcohol of cyclopropene. At room temperature, it is a stable white solid, soluble in diethyl ether, that decomposes (sometimes explosively) between 140 °C and 180 °C, and reacts slowly with water.

Croconic acid Chemical compound

Croconic acid or 4,5-dihydroxycyclopentenetrione is a chemical compound with formula C5H2O5 or (C=O)3(COH)2. It has a cyclopentene backbone with two hydroxyl groups adjacent to the double bond and three ketone groups on the remaining carbon atoms. It is sensitive to light, soluble in water and ethanol and forms yellow crystals that decompose at 212 °C.

Rhodizonic acid Chemical compound

Rhodizonic acid is a chemical compound with formula C6H2O6 or (CO)4(COH)2. It can be seen as a twofold enol and fourfold ketone of cyclohexene, more precisely 5,6-dihydroxycyclohex-5-ene-1,2,3,4-tetrone.

Acetylenedicarboxylic acid Chemical compound

Acetylenedicarboxylic acid or butynedioic acid is an organic compound (a dicarboxylic acid) with the formula C4H2O4 or HO2CC≡CCO2H. It is a crystalline solid that is soluble in diethyl ether.

Hydrogenoxalate Ion

Hydrogenoxalate or hydrogen oxalate is an anion with chemical formula HC
2
O
4
or HO
2
C–CO
2
, derived from oxalic acid by the loss of a single proton; or, alternatively, from the oxalate anion C
2
O2−
4
by addition of a proton. The name is also used for any salt containing this anion. Especially in older literature, hydrogenoxalates may also be referred to as bioxalates, acid oxalates, or monobasic oxalates. Hydrogenoxalate is amphoteric, in that it can react both as an acid or a base.

Oxocarbon anion

In chemistry, an oxocarbon anion is a negative ion consisting solely of carbon and oxygen atoms, and therefore having the general formula C
x
On
y
for some integers x, y, and n.

The carbonite ion is the double ionized ion of dihydroxymethylidene, with the chemical formula: CO2−
2
. Alkali metal salts, such as Li
2
CO
2
, K
2
CO
2
, and Cs
2
CO
2
, have been observed at 15 K. Due to the lone pair on the carbon atom, salts of the carbonite ion would be protonated to form formate and formic acid, rather than the carbene.

Magnesium oxalate Magnesium compound

Magnesium oxalate is an organic 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.

Sodium hydrogenoxalate Partly deprotonated oxalic acid

Sodium hydrogenoxalate is salt of formula NaHC
2
O
4
, consisting of sodium cations Na+
and hydrogenoxalate anions HC
2
O
4
or -. The anion can be described as the result of removing one hydrogen ion H+
from oxalic acid H
2
C
2
O
4
, or adding one to the oxalate anion C
2
O2−
4
.

Hydromelonic acid Chemical compound

Hydromelonic acid, is an elusive chemical compound with formula C
9
H
3
N
13
or (HNCN)
3
(C
6
N
7
)
, whose molecule would consist of a heptazine H3(C
6
N
7
)
molecule, with three cyanamido groups H–N=C=N– or N≡C–NH– substituted for the hydrogen atoms.

References

  1. "oxalate(2−) (CHEBI:30623)". www.ebi.ac.uk. Retrieved 2 January 2019. oxalate(2−) (CHEBI:30623) is conjugate base of oxalate(1−) (CHEBI:46904) … oxalate(1−) (CHEBI:46904) is conjugate acid of oxalate(2−) (CHEBI:30623)
  2. Riemenschneider, Wilhelm; Tanifuji, Minoru (2000). "Oxalic Acid". Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a18_247. ISBN   3-527-30673-0.
  3. 1 2 Dean, Philip A. W. (2012). "The Oxalate Dianion, C
    2
    O2−
    4
    : Planar or Nonplanar?". Journal of Chemical Education. 89 (3): 417–418. Bibcode:2012JChEd..89..417D. doi:10.1021/ed200202r.
  4. Reed, D. A.; Olmstead, M. M. (1981). "Sodium oxalate structure refinement" (PDF). Acta Crystallographica Section B. 37 (4): 938–939. doi:10.1107/S0567740881004676.
  5. Beagley, B.; Small, R. W. H. (1964). "The structure of lithium oxalate". Acta Crystallographica. 17 (6): 783–788. doi:10.1107/S0365110X64002079.
  6. In the figure 81(1)°, the (1) indicates that 1° is the standard uncertainty of the measured angle of 81°
  7. 1 2 3 Dinnebier, Robert E.; Vensky, Sascha; Panthöfer, Martin; Jansen, Martin (2003). "Crystal and Molecular Structures of Alkali Oxalates: First Proof of a Staggered Oxalate Anion in the Solid State". Inorganic Chemistry. 42 (5): 1499–1507. doi:10.1021/ic0205536. PMID   12611516.
  8. "CSD Entry WUWTIR: Di-cesium oxalate". Cambridge Structural Database: Access Structures. Cambridge Crystallographic Data Centre. doi:10.5517/cc6fzf0.
  9. "CSD Entry QQQAZJ03: Di-potassium oxalate". Cambridge Structural Database: Access Structures. Cambridge Crystallographic Data Centre. doi:10.5517/cc6fzcy.
  10. Clark, Timothy; Schleyer, Paul von Ragué (1981). "Conformational preferences of 34 valence electron A2X4 molecules: An ab initio Study of B2F4, B2Cl4, N2O4, and C
    2
    O2−
    4
    ". Journal of Computational Chemistry. 2: 20–29. doi:10.1002/jcc.540020106. S2CID   98744097.
  11. Dewar, Michael J.S.; Zheng, Ya-Jun (1990). "Structure of the oxalate ion". Journal of Molecular Structure: THEOCHEM. 209 (1–2): 157–162. doi:10.1016/0166-1280(90)85053-P.
  12. Herbert, John M.; Ortiz, J. V. (2000). "Ab Initio Investigation of Electron Detachment in Dicarboxylate Dianions". The Journal of Physical Chemistry A. 104 (50): 11786–11795. Bibcode:2000JPCA..10411786H. doi:10.1021/jp002657c.
  13. Streitweiser, Andrew, Jr.; Heathcock, Clayton H. (1976). Introduction to Organic Chemistry . Macmillan. p.  737.
  14. Resnick, Martin I.; Pak, Charles Y. C. (1990). Urolithiasis, A Medical and Surgical Reference. W.B. Saunders Company. p. 158. ISBN   0-7216-2439-1.
  15. Textbook of Orthopaedics, Trauma and Rheumatology (2nd ed.). Mosby Ltd. 2013. p. 204. ISBN   9780702056710.
  16. "UPMC Article, Low Oxalate Diet".
  17. "UMMC Condition Guide: Gout".
  18. Morozumi, Makoto; Hossain, Rayhan Zubair; Yamakawa, Ken'ichi; Hokama, Sanehiro; Nishijima, Saori; Oshiro, Yoshinori; Uchida, Atsushi; Sugaya, Kimio; Ogawa, Yoshihide (2006). "Gastrointestinal oxalic acid absorption in calcium-treated rats". Urological Research. 34 (3): 168–172. doi:10.1007/s00240-006-0035-7. PMID   16705467. S2CID   35167878.
  19. Hossain, R. Z.; Ogawa, Y.; Morozumi, M.; Hokama, S.; Sugaya, K. (2003). "Milk and calcium prevent gastrointestinal absorption and urinary excretion of oxalate in rats". Frontiers in Bioscience. 8 (1–3): a117–a125. doi:10.2741/1083. PMID   12700095.
  20. Pabuççuoğlu, Uğur (2005). "Aspects of oxalosis associated with aspergillosis in pathology specimens". Pathology – Research and Practice. 201 (5): 363–368. doi:10.1016/j.prp.2005.03.005. PMID   16047945.
  21. Syed, Fahd; Mena Gutiérrez, Alejandra; Ghaffar, Umbar (2 April 2015). "A Case of Iced-Tea Nephropathy". New England Journal of Medicine. 372 (14): 1377–1378. doi:10.1056/NEJMc1414481. PMID   25830441.
  22. Siener, R.; Bangen, U.; Sidhu, H.; Hönow, R.; von Unruh, G.; Hesse, A. (2013). "The role of Oxalobacter formigenes colonization in calcium oxalate stone disease". Kidney International. 83 (June): 1144–1149. doi: 10.1038/ki.2013.104 . PMID   23536130.

Further reading