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Oxalate

From Wikipedia, the free encyclopedia
Any derivative of oxalic acid; chemical compound containing oxalate moiety
Oxalate
two capital Cs connected to each other by a solid line and each connected to two separate Os by a solid line and a dashed line next to the solid line, the whole thing in brackets with a −2 to the top-right
The structure of the oxalate anion
Names
IUPAC name
Oxalate
Systematic IUPAC name
Ethanedioate[1]
Identifiers
3D model (JSmol)
1905970
ChEBI
ChemSpider
2207
KEGG
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
C2O2−4
Molar mass88.018 g·mol−1
Conjugate acidHydrogenoxalate[2]
Structure
D2h
Related compounds
Dinitrogen tetroxide
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa).
Chemical compound

Oxalate (systematic IUPAC name:ethanedioate) is ananion with thechemical formulaC2O2−4. Thisdianion is colorless. It occurs naturally, including in some foods. It forms a variety ofsalts, for examplesodium oxalate (Na2C2O4), and severalesters such asdimethyl oxalate ((CH3)2C2O4). It is aconjugate base ofoxalic acid. At neutralpH inaqueous solution, oxalic acid converts completely to oxalate.

Relationship to oxalic acid

[edit]

The dissociation ofprotons from oxalic acid proceeds in a stepwise manner; as for otherpolyprotic acids, loss of a single proton results in the monovalenthydrogenoxalate anionHC2O4. Asalt with thisanion is sometimes called anacid oxalate, monobasic oxalate, orhydrogen oxalate. Theequilibrium constant (Ka) for loss of the first proton is5.37×10−2 (pKa = 1.27). The loss of the second proton, which yields the oxalate ion, has an equilibrium constant of5.25×10−5 (pKa = 4.28). These values imply, in solutions with neutralpH, no oxalic acid and only trace amounts of hydrogen oxalate exist.[3] The literature is often unclear on the distinction betweenH2C2O4,HC2O4, andC2O2−4, and the collection of species is referred to as oxalic acid.[citation needed]

Structure

[edit]

The oxalate anion exists in a nonplanar conformation where the O–C–C–Odihedrals approach 90° with approximateD2d symmetry.[4] When chelated to cations, oxalate adopts the planar, D2h conformation.[5][6] However, in the structure ofcaesium oxalateCs2C2O4 the O–C–C–O dihedral angle is 81(1)°.[7][8] Therefore,Cs2C2O4 is more closely approximated by a D2d symmetry structure because the twoCO2 planes are staggered. Two structural forms ofrubidium oxalateRb2C2O4 have been identified by single-crystal X-ray diffraction: one contains a planar and the other a staggered oxalate.

Nonplanar conformation found incaesium oxalateCs2C2O4[8][9]
Planar conformation found in potassium oxalateK2C2O4[8][10]

Thebarrier to rotation about this bond is calculated to be roughly 2–6 kcal/mol for the free dianion,C2O2−4.[11][12][13] Such results are consistent with the interpretation that the centralC−C bond is regarded as asingle bond with minimalπ interactions between the twoCO2 units.[4] 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 toelectrostatic interactions as unfavorable O−O repulsion is maximized in the planar form.

Occurrence in nature

[edit]

Oxalate occurs in many plants, where it is synthesized by the incompleteoxidation ofsaccharides.

Several plant foods such as the root and/or leaves ofspinach,rhubarb, andbuckwheat are high in oxalic acid and can contribute to the formation of kidney stones in some individuals. Other oxalate-rich plants includefat hen ("lamb's quarters"),sorrel, and severalOxalis species (also sometimes called sorrels). The root and/or leaves of rhubarb and buckwheat are high in oxalic acid.[14] 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, mostnuts, mostberries,fishtail palms, New Zealand spinach (Tetragonia tetragonioides), andbeans.[citation needed]Leaves of thetea plant (Camellia sinensis) contain among the greatest measured concentrations of oxalic acid relative to other plants. However, the drink derived byinfusion 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]

Common high-oxalate foods[15]
Food itemServing
Oxalate
content
(mg)
Beetroot greens, cooked12cup916
Purslane, leaves, cooked12 cup910
Rhubarb, stewed, no sugar12 cup860
Spinach, cooked12 cup750
Beet, cooked12 cup675
Chard, Swiss, leaves cooked12 cup660
Rhubarb, canned12 cup600
Spinach, frozen12 cup600
Beet, pickled12 cup500
Poke greens, cooked12 cup476
Almond, raw1 oz296
Endive, raw20 long leaves273
Cocoa, dry13 cup254
Dandelion greens, cooked12 cup246
Okra, cooked8–9 pods146
Sweet potato, cooked12 cup141
Kale, cooked12 cup125
Peanuts, raw13 cup (1+34oz)113
Turnip greens, cooked12 cup110
Chocolate, unsweetened1 oz91
Parsnips, diced, cooked12 cup81
Collard greens, cooked12 cup74
Pecans, halves, raw13 cup (1+14 oz)74
Tea, leaves (4-minute infusion)1 leveltsp in 7fl oz water72
Cereal germ, toasted14 cup67
Gooseberries12 cup66
Potato, Idaho white, baked1 medium64
Carrots, cooked12 cup45
Apple, raw with skin1 medium41
Brussels sprouts, cooked6–8 medium37
Strawberries, raw12 cup35
Celery, raw2 stalks34
Milk chocolate bar1 bar (1.02 oz)
34
Raspberries, black, raw12 cup33
Orange, edible portion1 medium24
Green beans, cooked12 cup23
Chives, raw, chopped1tablespoon19
Leeks, raw12 medium15
Blackberries, raw12 cup13
Concord grapes12 cup13
Blueberries, raw12 cup11
Redcurrants12 cup11
Apricots, raw2 medium10
Raspberries, red, raw12 cup10
Broccoli, cooked1 large stalk6
Cranberry juice12 cup (4 oz)6

Physiological effects

[edit]
Main article:Kidney stone
Scanning electron micrograph of the surface of akidney stone showing tetragonal crystals ofweddellite (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 of oxalate-rich foods has been linked tokidney stone formation of metal ions, such ascalcium oxalate, arisk factor for kidney stones.[16]

Somefungi of thegenusAspergillus produce oxalic acid.[17]

As a ligand for metal ions

[edit]
Main article:Transition metal oxalate complex

Oxalate also formscoordination compounds where it is sometimes abbreviated asox. It is commonly encountered as abidentate ligand. When the oxalate chelates to a single metal center, it always adopts the planar conformation. As a bidentate ligand, it forms a 5-memberedMC2O2 ring. An illustrative complex ispotassium ferrioxalate,K3[Fe(C2O4)3]. The drugoxaliplatin exhibits improved water solubility relative to olderplatinum-based drugs, avoiding the dose-limiting side-effect ofnephrotoxicity. 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

[edit]

An excess oxalate level in the blood is termedhyperoxalemia, and high levels of oxalate in the urine is termedhyperoxaluria.

Acquired

[edit]

Although unusual, consumption of oxalates (for example, the grazing of animals on oxalate-containing plants such asBassia hyssopifolia, or human consumption ofwood sorrel or, specifically in excessive quantities,black tea) may result inkidney disease or evendeath 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 one gallon or 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 withoutproteinuria (an excess of protein in the urine) and with large amounts of calcium oxalate in urine sediment.[18]Oxalobacter formigenes in thegut flora may help alleviate this.[19]

Congenital

[edit]
Main article:Primary hyperoxaluria

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

References

[edit]
  1. ^"Oxalate".
  2. ^"oxalate(2−) (CHEBI:30623)".www.ebi.ac.uk. Retrieved2 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)
  3. ^Riemenschneider, Wilhelm; Tanifuji, Minoru (2000). "Oxalic Acid".Ullmann's Encyclopedia of Industrial Chemistry.doi:10.1002/14356007.a18_247.ISBN 3-527-30673-0.
  4. ^abDean, Philip A. W. (2012). "The Oxalate Dianion, C2O42-: Planar or Nonplanar?".Journal of Chemical Education.89 (3):417–418.Bibcode:2012JChEd..89..417D.doi:10.1021/ed200202r.
  5. ^Reed, D. A.; Olmstead, M. M. (1981)."Sodium oxalate structure refinement"(PDF).Acta Crystallographica Section B.37 (4):938–939.Bibcode:1981AcCrB..37..938R.doi:10.1107/S0567740881004676.
  6. ^Beagley, B.; Small, R. W. H. (1964)."The structure of lithium oxalate".Acta Crystallographica.17 (6):783–788.Bibcode:1964AcCry..17..783B.doi:10.1107/S0365110X64002079.
  7. ^In the figure 81(1)°, the (1) indicates that 1° is the standard uncertainty of the measured angle of 81°
  8. ^abcDinnebier, 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.
  9. ^Dinnebier, R.E.; Vensky, S.; Panthofer, M.; Jansen, M. (2003). "CSD Entry WUWTIR: Di-cesium oxalate".Cambridge Structural Database: Access Structures.Cambridge Crystallographic Data Centre.doi:10.5517/cc6fzf0.
  10. ^Dinnebier, R.E.; Vensky, S.; Panthofer, M.; Jansen, M. (2003). "CSD Entry QQQAZJ03: Di-potassium oxalate".Cambridge Structural Database: Access Structures.Cambridge Crystallographic Data Centre.doi:10.5517/cc6fzcy.
  11. ^Clark, Timothy; Schleyer, Paul von Ragué (1981). "Conformational preferences of 34 valence electron A2X4 molecules: Anab initio Study of B2F4, B2Cl4, N2O4, andC
    2
    O2−
    4
    ".Journal of Computational Chemistry.2:20–29.doi:10.1002/jcc.540020106.S2CID 98744097.
  12. ^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.
  13. ^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.
  14. ^Streitweiser, Andrew Jr.;Heathcock, Clayton H. (1976).Introduction to Organic Chemistry. Macmillan. p. 737.ISBN 9780024180100.
  15. ^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.
  16. ^Mitchell T, Kumar P, Reddy T, Wood KD, Knight J, Assimos DG, Holmes RP (March 2019)."Dietary oxalate and kidney stone formation".American Journal of Physiology. Renal Physiology.316 (3):F409 –F413.doi:10.1152/ajprenal.00373.2018.PMC 6459305.PMID 30566003.
  17. ^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.
  18. ^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.
  19. ^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

[edit]

External links

[edit]
  • Oxalate.org - Oxalate content of 750+ foods from university and government sources
  • Oxalatecontent.com - Oxalate content database based on the latest trustworthy studies
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