Oxalic acid

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Oxalic acid
Structural formula of oxalic acid
Skeletal formula of oxalic acid
Space-filling model of oxalic acid
Oxalic acid dihydrate
Names
IUPAC name
ethanedioic acid
Other names
oxalic acid, wood bleach
Identifiers
144-62-7 YesY
3DMet B00059
385686
ChEBI CHEBI:16995 YesY
ChEMBL ChEMBL146755 YesY
ChemSpider 946 YesY
DrugBank DB03902 YesY
EC Number 205-634-3
2208
Jmol interactive 3D Image
KEGG C00209 N
MeSH Oxalic+acid
PubChem 971
RTECS number RO2450000
UNII 9E7R5L6H31 YesY
UN number 3261
Properties
C2H2O4
Molar mass 90.03 g·mol−1
(anhydrous)
126.07 g mol−1 (dihydrate)
Appearance White crystals
Odor odorless
Density 1.90 g cm−3 (anhydrous)
1.653 g cm−3 (dihydrate)
Melting point 102 to 103 °C (216 to 217 °F; 375 to 376 K)
101.5 °C (214.7 °F; 374.6 K) dihydrate
143 g/L (25 °C)
Solubility 237 g/L (15 °C) in ethanol
14 g/L (15 °C) in diethyl ether [1]
Vapor pressure <0.001 mmHg (20 °C)[2]
Acidity (pKa) 1.25, 4.14[3]
Pharmacology
ATCvet code QP53AG03
Hazards
Main hazards Toxic T
Safety data sheet External MSDS
NFPA 704
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g., canola oil Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored 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)[4]
US health exposure limits (NIOSH):
TWA 1 mg/m3[2]
TWA 1 mg/m3 ST 2 mg/m3[2]
500 mg/m3[2]
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 YesYN ?)
Infobox references

Oxalic acid is an organic compound with the formula H2C2O4. It is a colorless crystalline solid that forms a colorless solution in water. Its condensed formula is HOOCCOOH, reflecting its classification as the simplest dicarboxylic acid. Its acid strength is much greater than that of acetic acid. Oxalic acid is a reducing agent [5] and its conjugate base, known as oxalate (C2O42−), is a chelating agent for metal cations. Typically, oxalic acid occurs as the dihydrate with the formula H2C2O4·2H2O. Excessive ingestion of oxalic acid or prolonged skin contact can be dangerous.

History[edit]

The preparation of salts of oxalic acid from plants had been known, at the latest, since 1745, when the Dutch botanist and physician Herman Boerhaave isolated a salt from sorrel.[6] By 1773, François Pierre Savary of Fribourg, Switzerland had isolated oxalic acid from its salt in sorrel.[7]

In 1776, Swedish chemists Carl Wilhelm Scheele and Torbern Olof Bergman[8] 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.[9]

In 1824, the German chemist Friedrich Wöhler obtained oxalic acid by reacting cyanogen with ammonia in aqueous solution.[10] This experiment may represent the first synthesis of a natural product.[11]

Preparation[edit]

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.[12] 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.[11]

Historically oxalic acid was obtained exclusively by using caustics, such as sodium or potassium hydroxide, on sawdust.[13]

Laboratory methods[edit]

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.[14]

The hydrated solid can be dehydrated with heat or by azeotropic distillation.[15]

Developed in the Netherlands, an electrocatalysis by a copper complex helps reduce carbon dioxide to oxalic acid;[16] this conversion uses carbon dioxide as a feedstock to generate oxalic acid.

Structure[edit]

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

Reactions[edit]

Oxalic acid is a relatively strong acid, despite being a carboxylic acid:

C2O4H2 is in equilibrium with C2O4H + H+; pKa = 1.27
C2O4H is in equilibrium with C2O42− + 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)).[18] It forms an acid chloride called oxalyl chloride.

Oxalate, the conjugate base of oxalic acid, is an excellent ligand for metal ions, e.g. the drug oxaliplatin.

Oxalic acid and oxalates can be oxidized by permanganate in an autocatalytic reaction.[19]

Occurrence[edit]

Biosynthesis[edit]

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:[20]

[O2CC(O)CH2CO2]2− + H2O → C2O42− + CH3CO2 + H+

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

Occurrence in foods and plants[edit]

Calcium oxalate is the most common component of kidney stones. 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.[21] Rhubarb leaves contain about 0.5% oxalic acid and jack-in-the-pulpit (Arisaema triphyllum) contains calcium oxalate crystals. Bacteria produce oxalates from oxidation of carbohydrates.[11]

Plants of the Fenestraria genus produce optical fibers made from crystalline oxalic acid to transmit light to subterranean photosynthetic sites.[22]

Other[edit]

Oxidized bitumen or bitumen exposed to gamma rays also contains oxalic acid among its degradation products. Oxalic acid may increase the leaching of radionuclides conditioned in bitumen for radioactive waste disposal.[23]

Biochemistry[edit]

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.[24] 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,[25] thus is an interesting potential course of cancer treatment.

Applications[edit]

About 25% of produced oxalic acid is used as a mordant in dyeing processes. It is used in bleaches, especially for pulpwood. It is also used in baking powder.[11] also used as a third reagent in silica analysis instruments.

Cleaning[edit]

Oxalic acid's main applications include cleaning or bleaching, especially for the removal of rust (iron complexing agent). Bar Keepers Friend is an example of a household cleaner containing oxalic acid. Its utility in rust removal agents is due to its forming a stable, water-soluble salt with ferric iron, ferrioxalate ion.

Extractive metallurgy[edit]

Oxalic acid is an important reagent in lanthanide chemistry. Hydrated lanthanide oxalates form readily in very strongly acidic solutions in a densely crystalline, easily filtered form, largely free of contamination by nonlanthanide elements. Thermal decomposition of these oxalate gives the oxides, which is the most commonly marketed form of these elements.

Niche uses[edit]

Honeybee coated with oxalic acid crystals

Vaporized oxalic acid, or a 3.2% solution of oxalic acid in sugar syrup, is used by some beekeepers as a miticide against the parasitic varroa mite.[26]

Oxalic acid is rubbed onto completed marble sculptures to seal the surface and introduce a shine. Oxalic acid is also used to clean iron and manganese deposits from quartz crystals.[27][28]

Oxalic acid is used as a bleach for wood, removing black stains caused by water penetration.

Content in food items[edit]

Vegetable Oxalic acid
(g/100 g)[29]
Amaranth 1.09
Asparagus 0.13
Beans, snap 0.36
Beet leaves 0.61
Broccoli 0.19
Brussels sprouts 0.36
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[30]
Rutabaga 0.03
Spinach 0.97
Squash 0.02
Sweet potato 0.24
Tomato 0.05
Turnip 0.21
Turnip greens 0.05
Watercress 0.31

Toxicity and safety[edit]

Oxalic acid in concentrated form can have harmful effects through contact and if ingested; manufacturers provide details in Material Safety Data Sheets (MSDS). It is not identified as mutagenic or carcinogenic; there is a possible risk of congenital malformation in the fetus; may be harmful if inhaled, and is extremely destructive to tissue of mucous membranes and upper respiratory tract; harmful if swallowed; harmful to and destructive of tissue and causes burns if absorbed through the skin or is in contact with the eyes. Symptoms and effects include a burning sensation, cough, wheezing, laryngitis, shortness of breath, spasm, inflammation and edema of the larynx, inflammation and edema of the bronchi, pneumonitis, pulmonary edema.[31]

In humans, ingested oxalic acid has an oral LDLo (lowest published lethal dose) of 600 mg/kg.[32] It has been reported that the lethal oral dose is 15 to 30 grams.[33]

The toxicity of oxalic acid is due to kidney failure caused by precipitation of solid calcium oxalate,[34] the main component of kidney stones. Oxalic acid can also cause joint pain due to the formation of similar precipitates in the joints. Ingestion of ethylene glycol results in oxalic acid as a metabolite which can also cause acute kidney failure.

References[edit]

  1. ^ Radiant Agro Chem. "Oxalic Acid MSDS". 
  2. ^ a b c d "NIOSH Pocket Guide to Chemical Hazards #0474". National Institute for Occupational Safety and Health (NIOSH). 
  3. ^ Bjerrum, J., et al. (1958) Stability Constants, Chemical Society, London.
  4. ^ "Oxalic acid". Immediately Dangerous to Life and Health. National Institute for Occupational Safety and Health (NIOSH). 
  5. ^ Ullmann's Encyclopedia of Industrial Chemistry. Wiley. 2005. pp. 17624/28029. ISBN 9783527306732. 
  6. ^ 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".
  7. ^ 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.
  8. ^ 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.
  9. ^ 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].)
  10. ^ 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.
  11. ^ a b c d Wilhelm Riemenschneider, Minoru Tanifuji "Oxalic acid" in Ullmann's Encyclopedia of Industrial Chemistry, 2002, Wiley-VCH, Weinheim. doi: 10.1002/14356007.a18_247.
  12. ^ 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
  13. ^ Von Wagner, Rudolf (1897). Manual of chemical technology. New York: D. Appleton & Co. p. 499. 
  14. ^ Practical Organic Chemistry by Julius B. Cohen, 1930 ed. preparation #42
  15. ^ Clarke H. T.;. Davis, A. W. (1941). "Oxalic acid (anhydrous)". Org. Synth.: 421. ; Coll. Vol. 1 
  16. ^ 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. doi:10.1126/science.1177981. 
  17. ^ Wells, A.F. (1984) Structural Inorganic Chemistry, Oxford: Clarendon Press. ISBN 0-19-855370-6.
  18. ^ Bowden, E. (1943). "Methyl oxalate". Org. Synth.: 414. ; Coll. Vol. 2 
  19. ^ Kovacs K.A., Grof P., Burai L., Riedel M. (2004). "Revising the mechanism of the permanganate/oxalate reaction". J. Phys. Chem. A 108 (50): 11026–11031. doi:10.1021/jp047061u. 
  20. ^ 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. .
  21. ^ Rombauer, Rombauer Becker, and Becker (1931/1997). Joy of Cooking, p.415. ISBN 0-684-81870-1.
  22. ^ 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.
  23. ^ EPJ Web of Conferences
  24. ^ 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. PMID 13654335. 
  25. ^ 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: 2037–2042. doi:10.1073/pnas.0914433107. 
  26. ^ Exploring New Methods for Varroa Mite Control, Yu-Lun Lisa Fu
  27. ^ Jackson, Faith. "Quartz Crystal Cleaning". bluemooncrystals.com
  28. ^ "Rock Currier – Cleaning Quartz". mindat.org
  29. ^ 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)
  30. ^ 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. 
  31. ^ Oxalic acid dihydrate. MSDS. sigmaaldrich.com
  32. ^ "Oxalic Acid Material Safety Data Sheet" (PDF). Radiant Indus Chem. Retrieved 2014-05-20. 
  33. ^ "CDC – Immediately Dangerous to Life or Health Concentrations (IDLH): Oxalic acid – NIOSH Publications and Products". cdc.gov
  34. ^ EMEA Committee for veterinary medicinal products, oxalic acid summary report, December 2003

External links[edit]