Oxalic acid

Oxalic acid
Structural formula of oxalic acid
Skeletal formula of oxalic acid
Space-filling model of oxalic acid
Names
Preferred IUPAC name
Oxalic acid[1]
Systematic IUPAC name
Ethanedioic acid[1]
Other names
Wood bleach, Crab Acid
Identifiers
CAS Number
3D model (JSmol)
3DMet
Beilstein Reference
 385686
ChEBI
ChEMBL
ChemSpider
DrugBank
ECHA InfoCard 100.005.123
Edit this at Wikidata
EC Number
  • 205-634-3
Gmelin Reference
 2208
KEGG
MeSH Oxalic+acid
PubChem CID
RTECS number
  • RO2450000
UNII
UN number 3261
InChI
  • InChI=1S/C6H6O6/c3-1(4)2(5)6/h(H,3,4)(H,5,6) checkY
    Key: MUBZPKHOEPUJKR-UHFFFAOYSA-N checkY
SMILES
  • OC(=O)C(=O)O
Properties
Chemical formula
 C2H2O4
Molar mass 90.034 g·mol−1 (anhydrous)
126.065 g·mol−1 (dihydrate)
Appearance White crystals
Odor Odorless
Density 1.90 g·cm−3 (anhydrous, at 17 °C)[2]
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
Solubility in water
 46.9 g/L (5 °C), 57.2 (10 °C), 75.5 (15 °C), 95.5 (20 °C), 118 (25 °C), 139 (30 °C), 178 (35 °C), 217 (40 °C), 261 (45 °C), 315 (50 °C), 376 (55 °C), 426 (60 °C), 548 (65 °C) [3]
Solubility 237 g/L (15 °C) in ethanol
14 g/L (15 °C) in diethyl ether[4]
Vapor pressure <0.001 mmHg (20 °C)[5]
Acidity (pKa) 1.25, 4.14[6]
Conjugate base Hydrogenoxalate
Magnetic susceptibility (χ)
 −60.05·10−6 cm3/mol
Pharmacology
QP53AG03 (WHO)
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 Corrosive
NFPA 704 (fire diamond)
Flash point 166 °C (331 °F; 439 K)
Lethal dose or concentration (LD, LC):
1000 mg/kg (dog, oral)
1400 mg/kg (rat)
7500 mg/kg (rat, oral)[7]
NIOSH (US health exposure limits):
PEL (Permissible)
 TWA 1 mg/m3[5]
REL (Recommended)
 TWA 1 mg/m3 ST 2 mg/m3[5]
IDLH (Immediate danger)
 500 mg/m3[5]
Safety data sheet (SDS) External MSDS
Related compounds
Related compounds
  • oxalyl chloride
  • disodium oxalate
  • calcium oxalate
  • phenyl oxalate ester
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)
Infobox references

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.

Oxalic acid has much greater acid strength than acetic acid. It is a reducing agent[8] and its conjugate base, known as oxalate (C2O2−4), is a chelating agent for metal cations. Typically, oxalic acid occurs as the dihydrate with the formula C2H2O4·2H2O.

History

The preparation of salts of oxalic acid (crab acid) from plants had been known, at least since 1745, when the Dutch botanist and physician Herman Boerhaave isolated a salt from wood sorrel.[9] By 1773, François Pierre Savary of Fribourg, Switzerland had isolated oxalic acid from its salt in sorrel.[10]

In 1776, Swedish chemists Carl Wilhelm Scheele and Torbern Olof Bergman[11] produced 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.[12]

In 1824, the German chemist Friedrich Wöhler obtained oxalic acid by reacting cyanogen with ammonia in aqueous solution.[13] This experiment may represent the first synthesis of a natural product.[14]

Preparation

Oxalic 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.[15] A newer method entails oxidative carbonylation of alcohols to give the diesters of oxalic acid:

4 ROH + 4 CO + O2 → 2 (CO2R)2 + 2 H2O

These diesters are subsequently hydrolyzed to oxalic acid. Approximately 120,000 tonnes are produced annually.[14]

Historically oxalic acid was obtained exclusively by using caustics, such as sodium or potassium hydroxide, on sawdust, followed by acidification of the oxalate by mineral acids, such as sulfuric acid.[16] Oxalic acid can also be formed by the heating of sodium formate in the presence of an alkaline catalyst.[17]

Laboratory methods

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.[18]

The hydrated solid can be dehydrated with heat or by azeotropic distillation.[19]

Developed in the Netherlands, an electrocatalysis by a copper complex helps reduce carbon dioxide to oxalic acid;[20] this conversion uses carbon dioxide as a feedstock to generate oxalic acid.

Structure

Anhydrous

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.[21] Because the anhydrous material is both acidic and hydrophilic (water seeking), it is used in esterifications.

Dihydrate

The dihydrate H
2C
2O
4.2H
2O has space group C52h–P21/n, with lattice parameters a = 611.9 pm, b = 360.7 pm, c = 1205.7 pm, β = 106°19', Z = 2.[22] The main inter-atomic distances are: C-C 153 pm, C-O1 129 pm, C-O2 119 pm.[23]

Theoretical studies indicate that oxalic acid dihydrate is one of very few crystalline substances that exhibit negative area compressibility. Namely, when subjected to isotropic tension stress (negative pressure), the a and c lattice parameters increase as the stress decreases from −1.17 GPa to −0.12 GPa and from −1.17 GPa to −0.51 GPa, respectively.[24]

Reactions

Acid-base properties

Oxalic acid's pKa values vary in the literature from 1.25–1.46 and 3.81–4.40.[25][26][27] The 100th ed of the CRC, released in 2019, has values of 1.25 and 3.81.[28] Oxalic acid is relatively strong compared to other carboxylic acids:

C2O4H2 ⇌ C2O4H− + H+          pKa = 1.27
C2O4H− ⇌ C
2O2−
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).[29] It forms an acid chloride called oxalyl chloride.

Metal-binding properties

Transition metal oxalate complexes are numerous, e.g. the drug oxaliplatin. Oxalic acid has shown to reduce manganese dioxide MnO
2 in manganese ores to allow the leaching of the metal by sulfuric acid.[30]

Oxalic acid is an important reagent in lanthanide chemistry. Hydrated lanthanide oxalates form readily in very strongly acidic solutions as a densely crystalline, easily filtered form, largely free of contamination by nonlanthanide elements:

2 Ln3+ + 3 C2O4H2 → Ln2(C2O4)3 + 6 H+

Thermal decomposition of these oxalates gives the oxides, which is the most commonly marketed form of these elements.[31]

Other

Oxalic acid and oxalates can be oxidized by permanganate in an autocatalytic reaction.[32]

Oxalic acid vapor decomposes at 125-175 °C into carbon dioxide CO
2 and formic acid HCOOH. Photolysis with 237-313 nm UV light also produces carbon monoxide CO and water.[33]

Evaporation of a solution of urea and oxalic acid in 2:1 molar ratio yields a solid crystalline compound H
2C
2O
4.[CO(NH
2)
2]
2, consisting of stacked two-dimensional networks of the neutral molecules held together by hydrogen bonds with the oxygen atoms.[34]

Occurrence

Biosynthesis

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:[35]

[O2CC(O)CH2CO2]2− + H2O → C
2O2−
4 + CH
3CO−
2 + H+

It also arises from the dehydrogenation of glycolic acid, which is produced by the metabolism of ethylene glycol.

Occurrence in foods and plants

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.[36] 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.[14]

Plants of the genus Fenestraria produce optical fibers made from crystalline oxalic acid to transmit light to subterranean photosynthetic sites.[37]

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.[38]

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.[39][40]

Production by fungi

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.[41][42] Some fungi such as Aspergillus niger have been extensively studied for the industrial production of oxalic acid;[43] however, those processes are not yet economically competitive with production from oil and gas.[44]

Biochemistry

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.[45] 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,[46] thus is an interesting potential course of cancer treatment.

Applications

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. The cleaning product Zud contains oxalic acid.[47] Oxalic acid is an ingredient in some tooth whitening products. About 25% of produced oxalic acid will be used as a mordant in dyeing processes. It is also used in bleaches, especially for pulpwood, and for rust removal and other cleaning, in baking powder,[14] and as a third reagent in silica analysis instruments.

Niche uses

Honeybee coated with oxalate crystals

Oxalic acid is used by some beekeepers as a miticide against the parasitic varroa mite.[48]

Dilute solutions (0.05–0.15 M) of oxalic acid can be used to remove iron from clays such as kaolinite to produce light-colored ceramics.[49]

Oxalic acid is used to clean minerals.[50][51]

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 also widely used as a wood bleach, most often in its crystalline form to be mixed with water to its proper dilution for use.

Content in food items

[52]

VegetableOxalic acid
(g/100 g)a
Amaranth 1.09
Asparagus 0.13
Beans, snap 0.36
Beet leaves 0.61
Beetroot 0.06[53]
Broccoli 0.19
Brussels sprouts 0.02[53]
Cabbage 0.10
Carrot 0.50
Cassava 1.26
Cauliflower 0.15
Celery 0.19
Chicory 0.2
Chives 1.48
Collards 0.45
Coriander 0.01
Corn, sweet 0.01
Cucumber 0.02
Eggplant 0.19
Endive 0.11
Garlic 0.36
Kale 0.02
Lettuce 0.33
Okra 0.05
Onion 0.05
Parsley 1.70
Parsnip 0.04
Pea 0.05
Bell pepper 0.04
Potato 0.05
Purslane 1.31
Radish 0.48
Rhubarb leaves 0.52[54]
Rutabaga 0.03
Spinach 0.97 (ranges from .65 to 1.3 grams per 100 grams on fresh weight basis)[55]
Squash 0.02
Sweet potato 0.24
Swiss Chard, green 0.96 [53]
Tomato 0.05
Turnip 0.21
Turnip greens 0.05
Watercress 0.31

Toxicity

Oxalic acid has an oral LDLo (lowest published lethal dose) of 600 mg/kg.[56] It has been reported that the lethal oral dose is 15 to 30 grams.[57] The toxicity of oxalic acid is due to kidney failure caused by precipitation of solid calcium oxalate.[58]

Oxalate is known to cause mitochondrial dysfunction.[59]

Ingestion of ethylene glycol results in oxalic acid as a metabolite which can also cause acute kidney failure.

Kidney stones

The most kidney stones, 76%, are composed of the calcium salt of oxalic acid.[60] Oxalic acid can also cause joint pain by formation of similar precipitates in the joints. Calcium hydroxide decreases urinary oxalate in both humans and rats.[61] Ingesting both calcium containing foods, such as milk, with food high in oxalic acid, cause the formation of calcium oxalate in the stomach, which is not absorbed into the body.

Notes

^a Unless otherwise cited, all measurements are based on raw vegetable weights with original moisture content.

References

  1. 1 2 "Front Matter". Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. pp. P001–P004. doi:10.1039/9781849733069-FP001. ISBN 978-0-85404-182-4.
  2. ↑ Record in the GESTIS Substance Database of the Institute for Occupational Safety and Health
  3. ↑ Alexander Apelblat and Emanuel Manzurola (1987): "Solubility of oxalic, malonic, succinic, adipic, maleic, malic, citric, and tartaric acids in water from 278.15 to 338.15 K". The Journal of Chemical Thermodynamics, volume 19, issue 3, pages 317-320 doi:10.1016/0021-9614(87)90139-X
  4. ↑ Radiant Agro Chem. "Oxalic Acid MSDS". Archived from the original on 2011-07-15. Retrieved 2012-02-02.
  5. 1 2 3 4 NIOSH Pocket Guide to Chemical Hazards. "#0474". National Institute for Occupational Safety and Health (NIOSH).
  6. ↑ Bjerrum, Jannik; Sillén, Lars Gunnar; Schwarzenbach, Gerold Karl; Anderegg, Giorgio (1958). Stability constants of metal-ion complexes, with solubility products of inorganic substances. London: Chemical Society.
  7. ↑ "Oxalic acid". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
  8. ↑ Ullmann's Encyclopedia of Industrial Chemistry. Wiley. 2005. pp. 17624/28029. doi:10.1002/14356007. ISBN 9783527306732.
  9. ↑ See:
    • Herman Boerhaave, Elementa Chemiae (Basil, Switzerland: Johann Rudolph Im-hoff, 1745), volume 2, pp. 35-38. (in Latin) From p. 35: "Processus VII. Sal nativum plantarum paratus de succo illarum recens presso. Hic Acetosae." (Procedure 7. A natural salt of plants prepared from their freshly pressed juice. This [salt obtained] from sorrel.)
    • Henry Enfield Roscoe and Carl Schorlemmer, ed.s, A Treatise on Chemistry (New York, New York: D. Appleton and Co., 1890), volume 3, part 2, p. 105.
    • See also Wikipedia's articles "Oxalis acetosella" and "Potassium hydrogen oxalate".
  10. ↑ See:
    • François Pierre Savary, Dissertatio Inauguralis De Sale Essentiali Acetosellæ [Inaugural dissertation on the essential salt of wood sorrel] (Jean François Le Roux, 1773). (in Latin) Savary noticed that when he distilled sorrel salt (potassium hydrogen oxalate), crystals would sublimate onto the receiver. From p. 17: "Unum adhuc circa liquorem acidum, quem sal acetosellae tam sincerissimum a nobis paratum quam venale destillatione fundit phoenomenon erit notandum, nimirum quod aliquid ejus sub forma sicca crystallina lateribus excipuli accrescat, ..." (One more [thing] will be noted regarding the acid liquid, which furnished for us sorrel salt as pure as commercial distillations, [it] produces a phenomenon, that evidently something in dry, crystalline form grows on the sides of the receiver, ...) These were crystals of oxalic acid.
    • Leopold Gmelin with Henry Watts, trans., Hand-book of Chemistry (London, England: Cavendish Society, 1855), volume 9, p. 111.
  11. ↑ See:
    • Torbern Bergman with Johan Afzelius (1776) Dissertatio chemica de acido sacchari [Chemical dissertation on sugar acid] (Uppsala, Sweden: Edman, 1776).
    • Torbern Bergman, Opuscula Physica et Chemica, (Leipzig (Lipsia), (Germany): I.G. Müller, 1776), volume 1, "VIII. De acido Sacchari," pp. 238-263.
  12. ↑ Carl Wilhelm Scheele (1784) "Om Rhabarber-jordens bestånds-delar, samt sått at tilreda Acetosell-syran" (On rhubarb-earth's constituents, as well as ways of preparing sorrel-acid), Kungliga Vetenskapsakademiens Nya Handlingar [New Proceedings of the Royal Academy of Science], 2nd series, 5 : 183-187. (in Swedish) From p. 187: "Således finnes just samma syra som vi genom konst af socker med tilhjelp af salpeter-syra tilreda, redan förut af naturen tilredd uti o̊rten Acetosella." (Thus it is concluded [that] the very same acid as we prepare artificially by means of sugar with the help of nitric acid, [was] previously prepared naturally in the herb acetosella [i.e., sorrel].)
  13. ↑ See:
    • F. Wöhler (1824) "Om några föreningar af Cyan" (On some compounds of cyanide), Kungliga Vetenskapsakademiens Handlingar [Proceedings of the Royal Academy of Science], pp. 328-333. (in Swedish)
    • Reprinted in German as: F. Wöhler (1825) "Ueber Cyan-Verbindungen" (On cyanide compounds), Annalen der Physik und Chemie, 2nd series, 3 : 177-182.
  14. 1 2 3 4 Wilhelm Riemenschneider, Minoru Tanifuji "Oxalic acid" in Ullmann's Encyclopedia of Industrial Chemistry, 2002, Wiley-VCH, Weinheim. doi: 10.1002/14356007.a18_247.
  15. ↑ Eiichi, Yonemitsu; Tomiya, Isshiki; Tsuyoshi, Suzuki and Yukio, Yashima "Process for the production of oxalic acid", U.S. Patent 3,678,107, priority date March 15, 1969
  16. ↑ Von Wagner, Rudolf (1897). Manual of chemical technology. New York: D. Appleton & Co. p. 499.
  17. ↑ "Oxalic acid | Formula, Uses, & Facts | Britannica".
  18. ↑ Practical Organic Chemistry by Julius B. Cohen, 1930 ed. preparation #42
  19. ↑ Clarke H. T.;. Davis, A. W. (1941). "Oxalic acid (anhydrous)". Organic Syntheses: 421.{{cite journal}}: CS1 maint: multiple names: authors list (link); Collective Volume, vol. 1
  20. ↑ Bouwman, Elisabeth; Angamuthu, Raja; Byers, Philip; Lutz, Martin; Spek, Anthony L. (July 15, 2010). "Electrocatalytic CO2 Conversion to Oxalate by a Copper Complex". Science. 327 (5393): 313–315. Bibcode:2010Sci...327..313A. CiteSeerX 10.1.1.1009.2076. doi:10.1126/science.1177981. PMID 20075248. S2CID 24938351.
  21. ↑ Wells, A.F. (1984) Structural Inorganic Chemistry, Oxford: Clarendon Press. ISBN 0-19-855370-6.
  22. ↑ T. M. Sabine, G. W. Cox and B. M. Craven (1969): "A neutron diffraction study of [alpha]-oxalic acid dihydrate" Acta Crystallographica Section B, volume B25, pages 2437-2441. doi:10.1107/S0567740869005905
  23. ↑ F. R. Ahmed and D. W. J. Cruickshank (1953): "A refinement of the crystal structure analyses of oxalic acid dihydrate". Acta Crystallographica volume 6, pages 385-392. doi:10.1107/S0365110X53001083
  24. ↑ Francisco Colmenero (2019): "Negative area compressibility in oxalic acid dihydrate". Materials Letters, volume 245, pages 25-28. doi:10.1016/j.matlet.2019.02.077
  25. ↑ Bjerrum, J., et al. (1958) Stability Constants, Chemical Society, London.
  26. ↑ Haynes, W. M. (Ed.). (2014). CRC Handbook of Chemistry and Physics, 95th Edition (95 edition). Boca Raton; London; New York: CRC Press.
  27. ↑ Clayton, G. D. and Clayton, F. E. (eds.). Patty's Industrial Hygiene and Toxicology, Volume 2A, 2B, 2C: Toxicology. 3rd ed. New York: John Wiley Sons, 1981–1982., p. 4936
  28. ↑ Rumble, J. (Ed.). (2019). CRC Handbook of Chemistry and Physics, 100th Edition (100 edition). CRC Press.
  29. ↑ Bowden, E. (1943). "Methyl oxalate". Organic Syntheses: 414.; Collective Volume, vol. 2
  30. ↑ Sahoo, R. N.; Naik, P. K.; Das, S. C. (December 2001). "Leaching of manganese from low-grade manganese ore using oxalic acid as reductant in sulphuric acid solution". Hydrometallurgy. 62 (3): 157–163. doi:10.1016/S0304-386X(01)00196-7. Retrieved 4 December 2021.
  31. ↑ DezhiQi (2018). "Extraction of Rare Earths From RE Concentrates". Hydrometallurgy of Rare Earths Separation and Extraction. p. 1-185. doi:10.1016/B978-0-12-813920-2.00001-5. ISBN 9780128139202.
  32. ↑ Kovacs K. A.; Grof P.; Burai L.; Riedel M. (2004). "Revising the mechanism of the permanganate/oxalate reaction". Journal of Physical Chemistry A. 108 (50): 11026–11031. Bibcode:2004JPCA..10811026K. doi:10.1021/jp047061u.
  33. ↑ James Higgins, Xuefeng Zhou, Ruifeng Liu, and Thomas T.-S. Huang (1997): "Theoretical Study of Thermal Decomposition Mechanism of Oxalic Acid" Journal of Physical Chemistry A, volume 101, issue 14, pages 2702–2708. doi:10.1021/jp9638191
  34. ↑ S. Harkema, J. W. Bats, A. M. Weyenberg and D. Feil (1972) "The crystal structure of urea oxalic acid (2:1)". Acta Crystallographica Section B, volume B28, pages 1646-1648. doi:10.1107/S0567740872004789
  35. ↑ Dutton, M. V.; Evans, C. S. (1996). "Oxalate production by fungi: Its role in pathogenicity and ecology in the soil environment". Canadian Journal of Microbiology. 42 (9): 881–895. doi:10.1139/m96-114..
  36. ↑ Rombauer, Rombauer Becker, and Becker (1931/1997). Joy of Cooking, p.415. ISBN 0-684-81870-1.
  37. ↑ Attenborough, David. "Surviving." The Private Life of Plants: A Natural History of Plant Behaviour. Princeton, NJ: Princeton UP, 1995. 265+. "OpenLibrary.org: The Private Life of Plants" Print.
  38. ↑ Duarte, A.; Caixeirinho, D.; Miguel, M.; Sustelo, V.; Nunes, C.; Fernandes, M.; Marreiros, A. (2012). "Organic Acids Concentration in Citrus Juice from Conventional versus Organic Farming". Acta Horticulturae. 933 (933): 601–606. doi:10.17660/ActaHortic.2012.933.78. hdl:10400.1/2790.
  39. ↑ Sabbioni, Cristina; Zappia, Giuseppe (2016). "Oxalate patinas on ancient monuments: The biological hypothesis". Aerobiologia. 7: 31–37. doi:10.1007/BF02450015. S2CID 85017563.
  40. ↑ Frank-Kamemetskaya, Olga; Rusakov, Alexey; Barinova, Ekaterina; Zelenskaya, Marina; Vlasov, Dmitrij (2012). "The Formation of Oxalate Patina on the Surface of Carbonate Rocks Under the Influence of Microorganisms". Proceedings of the 10th International Congress for Applied Mineralogy (ICAM). pp. 213–220. doi:10.1007/978-3-642-27682-8_27. ISBN 978-3-642-27681-1.
  41. ↑ Dutton, Martin V.; Evans, Christine S. (1 September 1996). "Oxalate production by fungi: its role in pathogenicity and ecology in the soil environment". Canadian Journal of Microbiology. 42 (9): 881–895. doi:10.1139/m96-114.
  42. ↑ Gadd, Geoffrey M. (1 January 1999). "Fungal Production of Citric and Oxalic Acid: Importance in Metal Speciation, Physiology and Biogeochemical Processes". Advances in Microbial Physiology. Academic Press. 41: 47–92. doi:10.1016/S0065-2911(08)60165-4. ISBN 9780120277414. PMID 10500844.
  43. ↑ Hermann Strasser, Wolfgang Burgstaller, Franz Schinner(1994): "High-yield production of oxalic acid for metal leaching processes by Aspergillus niger". FEMS Microbiology Letters, volume 119, issue 3, pages 365–370. doi:10.1111/j.1574-6968.1994.tb06914.x
  44. ↑ Jan S. Tkacz, Lene Lange (2012): Advances in Fungal Biotechnology for Industry, Agriculture, and Medicine. 445 pages. ISBN 9781441988591
  45. ↑ Novoa, William; Alfred Winer; Andrew Glaid; George Schwert (1958). "Lactic Dehydrogenase V. inhibition by Oxamate and Oxalate". Journal of Biological Chemistry. 234 (5): 1143–8. doi:10.1016/S0021-9258(18)98146-9. PMID 13654335.
  46. ↑ Le, Anne; Charles Cooper; Arvin Gouw; Ramani Dinavahi; Anirban Maitra; Lorraine Deck; Robert Royer; David Vander Jagt; Gregg Semenza; Chi Dang (14 December 2009). "Inhibition of lactate dehydrogenase A induces oxidative stress and inhibits tumor progression". Proceedings of the National Academy of Sciences. 107 (5): 2037–2042. doi:10.1073/pnas.0914433107. PMC 2836706. PMID 20133848.
  47. ↑ "Oxalic Acid Best Treatment For Getting Rid Of Concrete Stains". The Hartford Courant. 7 August 2011. Retrieved 14 January 2021.
  48. ↑ Yu-Lun Lisa Fu (2008). Exploring New Methods for Varroa Mite Control. Michigan State University.
  49. ↑ Sung Oh Lee, Tam Tran, Byoung Hi Jung, Seong Jun Kim, and Myong Jun Kim (2007): "Dissolution of iron oxide using oxalic acid". Hydrometallurgy, volume 87, issues 3–4. pages 91-99. doi:10.1016/j.hydromet.2007.02.005
  50. ↑ Jackson, Faith. "Quartz Crystal Cleaning" Archived 2013-10-29 at the Wayback Machine. bluemooncrystals.com
  51. ↑ "Rock Currier – Cleaning Quartz". mindat.org
  52. ↑ All data not specifically annotated is from Agriculture Handbook No. 8-11, Vegetables and Vegetable Products, 1984. ("Nutrient Data : Oxalic Acid Content of Selected Vegetables". ars.usda.gov)
  53. 1 2 3 Chai, Weiwen; Liebman, Michael (2005). "Effect of Different Cooking Methods on Vegetable Oxalate Content". Journal of Agricultural and Food Chemistry. 53 (8): 3027–30. doi:10.1021/jf048128d. PMID 15826055.
  54. ↑ Pucher, GW; Wakeman, AJ; Vickery, HB (1938). "The organic acids of rhubarb (Rheum hybridium). III. The behavior of the organic acids during culture of excised leaves". Journal of Biological Chemistry. 126 (1): 43. doi:10.1016/S0021-9258(18)73892-1.
  55. ↑ Durham, Sharon. "Making Spinach with Low Oxalate Levels". AgResearch Magazine. No. January 2017. United States Department of Agriculture. Retrieved 26 June 2017. 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.
  56. ↑ "Oxalic Acid Material Safety Data Sheet" (PDF). Radiant Indus Chem. Archived from the original (PDF) on 2014-05-20. Retrieved 2014-05-20.
  57. ↑ "CDC – Immediately Dangerous to Life or Health Concentrations (IDLH): Oxalic acid – NIOSH Publications and Products". cdc.gov
  58. ↑ EMEA Committee for veterinary medicinal products, oxalic acid summary report, December 2003
  59. ↑ Patel, Mikita; Yarlagadda, Vidhush; Adedoyin, Oreoluwa; Saini, Vikram; Assimos, Dean G.; Holmes, Ross P.; Mitchell, Tanecia (May 2018). "Oxalate induces mitochondrial dysfunction and disrupts redox homeostasis in a human monocyte derived cell line". Redox Biology. 15: 207–215. doi:10.1016/j.redox.2017.12.003. PMC 5975227. PMID 29272854.
  60. ↑ Singh, Prince; Enders, Felicity T.; Vaughan, Lisa E.; Bergstralh, Eric J.; Knoedler, John J.; Krambeck, Amy E.; Lieske, John C.; Rule, Andrew D. (October 2015). "Stone Composition Among First-Time Symptomatic Kidney Stone Formers in the Community". Mayo Clinic Proceedings. 90 (10): 1356–1365. doi:10.1016/j.mayocp.2015.07.016. PMC 4593754. PMID 26349951.
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