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.
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 2O− 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 2O− 4, and C 2O2− 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.
Nonplanar conformation found in caesium oxalate[7][8]
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 2O2− 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 saccharides.
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 drink 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]
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]
Oxalate also forms coordination compounds where it is sometimes abbreviated as ox. It is commonly encountered as a bidentate ligand. 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]
Primary hyperoxaluria is a rare, inherited condition, resulting in increased excretion of oxalate, with oxalate stones being common.
References
^"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)
^ abDean, Philip A. W. (2012). "The Oxalate Dianion, C 2O2− 4: Planar or Nonplanar?". Journal of Chemical Education. 89 (3): 417–418. Bibcode:2012JChEd..89..417D. doi:10.1021/ed200202r.
^Reed, D. A.; Olmstead, M. M. (1981). "Sodium oxalate structure refinement" (PDF). Acta Crystallographica Section B. 37 (4): 938–939. doi:10.1107/S0567740881004676.
^Beagley, B.; Small, R. W. H. (1964). "The structure of lithium oxalate". Acta Crystallographica. 17 (6): 783–788. doi:10.1107/S0365110X64002079.
^In the figure 81(1)°, the (1) indicates that 1° is the standard uncertainty of the measured angle of 81°
^ 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.
^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 2O2− 4". Journal of Computational Chemistry. 2: 20–29. doi:10.1002/jcc.540020106. S2CID 98744097.
^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.
^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.
^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.
^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.
^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.
^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
Euler. "Ksp Table: Solubility product constants near 25 °C". chm.uri.edu. Retrieved 10 June 2021.
Ibis, Fatma; Dhand, Priya; Suleymanli, Sanan; van der Heijden, Antoine E. D. M.; Kramer, Herman J. M.; Eral, Huseyin Burak (2020). "A combined experimental and modelling study on solubility of calcium oxalate monohydrate at physiologically relevant pH and temperatures". Crystals. 10 (10): 924. doi:10.3390/cryst10100924. ISSN 2073-4352.
Ulmgren, Per; Rådeström, Rune (1999). "Solubility of calcium oxalate in the presence of magnesium ions, and solubility of magnesium oxalate in sodium chloride medium". Nordic Pulp & Paper Research Journal. 14 (4): 330–335. doi:10.3183/npprj-1999-14-04-p330-335. ISSN 2000-0669.
External links
Oxalate.org - Oxalate content of 750+ foods from university and government sources
February 27, 2023
oxalate, iupac, ethanedioate, anion, with, formula, c2o42, this, dianion, colorless, occurs, naturally, including, some, foods, forms, variety, salts, example, sodium, oxalate, na2c2o4, several, esters, such, dimethyl, oxalate, c2o4, conjugate, base, oxalic, a. 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 Oxalate The structure of the oxalate anionNamesPreferred IUPAC name OxalateIdentifiersCAS Number 338 70 5 Y3D model JSmol Interactive imageBeilstein Reference 1905970ChEBI CHEBI 30623ChemSpider 64235Gmelin Reference 2207KEGG C00209PubChem CID 71081UNII PQ7QG47K6T YInChI InChI 1S C2H2O4 c3 1 4 2 5 6 h H 3 4 H 5 6 p 2Key MUBZPKHOEPUJKR UHFFFAOYSA LInChI 1S C2H2O4 c3 1 4 2 5 6 h H 3 4 H 5 6 p 2Key MUBZPKHOEPUJKR UHFFFAOYSA LSMILES C O C O O O PropertiesChemical formula C2 O2 4Molar mass 88 019 g mol 1Conjugate acid Hydrogenoxalate 1 StructurePoint group D2hRelated compoundsRelated isoelectronic dinitrogen tetroxideExcept where otherwise noted data are given for materials in their standard state at 25 C 77 F 100 kPa Infobox references Contents 1 Relationship to oxalic acid 2 Structure 3 Occurrence in nature 3 1 Physiological effects 4 As a ligand for metal ions 5 Excess 5 1 Acquired 5 2 Congenital 6 References 7 Further reading 8 External linksRelationship to oxalic acid EditThe 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 HC2 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 HC2 O 4 and C2 O2 4 and the collection of species is referred to as oxalic acid citation needed Structure EditThe 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 Nonplanar conformation found in caesium oxalate 7 8 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 C2 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 p 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 EditOxalate occurs in many plants where it is synthesized by the incomplete oxidation of saccharides 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 drink 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 Common high oxalate foods 14 Food item Serving Oxalatecontent mg Beetroot greens cooked 1 2 cup unit 916Purslane leaves cooked 1 2 cup 910Rhubarb stewed no sugar 1 2 cup 860Spinach cooked 1 2 cup 750Beet cooked 1 2 cup 675Chard Swiss leaves cooked 1 2 cup 660Rhubarb canned 1 2 cup 600Spinach frozen 1 2 cup 600Beet pickled 1 2 cup 500Poke greens cooked 1 2 cup 476Endive raw 20 long leaves 273Cocoa dry 1 3 cup 254Dandelion greens cooked 1 2 cup 246Okra cooked 8 9 pods 146Sweet potato cooked 1 2 cup 141Kale cooked 1 2 cup 125Peanuts raw 1 3 cup 1 3 4 oz 113Turnip greens cooked 1 2 cup 110Chocolate unsweetened 1 oz 91Parsnips diced cooked 1 2 cup 81Collard greens cooked 1 2 cup 74Pecans halves raw 1 3 cup 1 1 4 oz 74Tea leaves 4 minute infusion 1 level tsp in 7 fl oz water 72Cereal germ toasted 1 4 cup 67Gooseberries 1 2 cup 66Potato Idaho white baked 1 medium 64Carrots cooked 1 2 cup 45Apple raw with skin 1 medium 41Brussels sprouts cooked 6 8 medium 37Strawberries raw 1 2 cup 35Celery raw 2 stalks 34Milk chocolate bar 1 bar 1 02 oz clarification needed 34Raspberries black raw 1 2 cup 33Orange edible portion 1 medium 24Green beans cooked 1 2 cup 23Chives raw chopped 1 tablespoon 19Leeks raw 1 2 medium 15Blackberries raw 1 2 cup 13Concord grapes 1 2 cup 13Blueberries raw 1 2 cup 11Redcurrants 1 2 cup 11Apricots raw 2 medium 10Raspberries red raw 1 2 cup 10Broccoli cooked 1 large stalk 6Cranberry juice 1 2 cup 4 oz 6Physiological effects Edit Main article Kidney stone 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 mg 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 EditMain article Transition metal oxalate complex Oxalate also forms coordination compounds where it is sometimes abbreviated as ox It is commonly encountered as a bidentate ligand 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 EditAn excess oxalate level in the blood is termed hyperoxalemia and high levels of oxalate in the urine is termed hyperoxaluria Acquired Edit 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 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 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 Riemenschneider Wilhelm Tanifuji Minoru 2000 Oxalic Acid Ullmann s Encyclopedia of Industrial Chemistry doi 10 1002 14356007 a18 247 ISBN 3 527 30673 0 a b Dean Philip A W 2012 The Oxalate Dianion C2 O2 4 Planar or Nonplanar Journal of Chemical Education 89 3 417 418 Bibcode 2012JChEd 89 417D doi 10 1021 ed200202r Reed D A Olmstead M M 1981 Sodium oxalate structure refinement PDF Acta Crystallographica Section B 37 4 938 939 doi 10 1107 S0567740881004676 Beagley B Small R W H 1964 The structure of lithium oxalate Acta Crystallographica 17 6 783 788 doi 10 1107 S0365110X64002079 In the figure 81 1 the 1 indicates that 1 is the standard uncertainty of the measured angle of 81 a b c Dinnebier Robert E Vensky Sascha Panthofer 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 CSD Entry WUWTIR Di cesium oxalate Cambridge Structural Database Access Structures Cambridge Crystallographic Data Centre doi 10 5517 cc6fzf0 CSD Entry QQQAZJ03 Di potassium oxalate Cambridge Structural Database Access Structures Cambridge Crystallographic Data Centre doi 10 5517 cc6fzcy Clark Timothy Schleyer Paul von Rague 1981 Conformational preferences of 34 valence electron A2X4 molecules An ab initio Study of B2F4 B2Cl4 N2O4 and C2 O2 4 Journal of Computational Chemistry 2 20 29 doi 10 1002 jcc 540020106 S2CID 98744097 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 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 Streitweiser Andrew Jr Heathcock Clayton H 1976 Introduction to Organic Chemistry Macmillan p 737 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 Textbook of Orthopaedics Trauma and Rheumatology 2nd ed Mosby Ltd 2013 p 204 ISBN 9780702056710 UPMC Article Low Oxalate Diet UMMC Condition Guide Gout 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 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 Pabuccuoglu Ugur 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 Syed Fahd Mena Gutierrez 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 Siener R Bangen U Sidhu H Honow 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 EditEuler Ksp Table Solubility product constants near 25 C chm uri edu Retrieved 10 June 2021 Ibis Fatma Dhand Priya Suleymanli Sanan van der Heijden Antoine E D M Kramer Herman J M Eral Huseyin Burak 2020 A combined experimental and modelling study on solubility of calcium oxalate monohydrate at physiologically relevant pH and temperatures Crystals 10 10 924 doi 10 3390 cryst10100924 ISSN 2073 4352 Ulmgren Per Radestrom Rune 1999 Solubility of calcium oxalate in the presence of magnesium ions and solubility of magnesium oxalate in sodium chloride medium Nordic Pulp amp Paper Research Journal 14 4 330 335 doi 10 3183 npprj 1999 14 04 p330 335 ISSN 2000 0669 External links EditOxalate org Oxalate content of 750 foods from university and government sources Retrieved from https en wikipedia org w index php title Oxalate amp oldid 1133376035, wikipedia, wiki, book, books, library,
