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Formic acid

Updated: 2017-09-09T09:23Z
Formic acid
Skeletal structure of formic acid
3D model of formic acid
Formic acid 85 percent.jpg
Preferred IUPAC name
Formic acid[1]
Systematic IUPAC name
Methanoic acid[1]
Other names
Carbonous acid; Formylic acid; Hydrogen carboxylic acid; Hydroxy(oxo)methane; Metacarbonoic acid; Oxocarbinic acid; Oxomethanol
3D model (JSmol)
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EC Number200-579-1
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RTECS numberLQ4900000
Molar mass46.03 g·mol−1
AppearanceColorless fuming liquid
OdorPungent, penetrating
Density1.220 g/mL
Melting point8.4 °C (47.1 °F; 281.5 K)
Boiling point100.8 °C (213.4 °F; 373.9 K)
SolubilityMiscible with ether, acetone, ethyl acetate, glycerol, methanol, ethanol
Partially soluble in benzene, toluene, xylenes
log P−0.54
Vapor pressure35 mmHg (20 °C)[2]
Acidity (pKa)3.77[3]
-19.90·10−6 cm3/mol
1.3714 (20 °C)
Viscosity1.57 cP at 268 °C
1.41 D (gas)
131.8 J/mol K
−425.0 kJ/mol
−254.6 kJ/mol
QP53AG01 (WHO)
Main hazardsCorrosive; irritant;
Safety data sheetSee: data page
JT Baker
R-phrases (outdated)R10 R35
S-phrases (outdated)(S1/2) S23 S26 S45
NFPA 704
Flash point69 °C (156 °F; 342 K)
601 °C (1,114 °F; 874 K)
Explosive limits14–34%[citation needed]
18%–57% (90% solution)[2]
Lethal dose or concentration (LD, LC):
700 mg/kg (mouse, oral), 1100 mg/kg (rat, oral), 4000 mg/kg (dog, oral)[4]
7853 ppm (rat, 15 min)
3246 ppm (mouse, 15 min)[4]
US health exposure limits (NIOSH):
PEL (Permissible)
TWA 5 ppm (9 mg/m3)[2]
REL (Recommended)
TWA 5 ppm (9 mg/m3)[2]
IDLH (Immediate danger)
30 ppm[2]
Related compounds
Acetic acid
Propionic acid
Related compounds
Supplementary data page
Refractive index (n),
Dielectric constantr), etc.
Phase behaviour
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

Formic acid, systemically named methanoic acid, is the simplest carboxylic acid. The chemical formula is HCOOH or HCO2H. It is an important intermediate in chemical synthesis and occurs naturally, most notably in some ants. The word "formic" comes from the Latin word for ant, formica, referring to its early isolation by the distillation of ant bodies, and the trivial name in some languages means "ant-acid", such as Dutch mierenzuur, Danish myresyre, Faroese meyrusýra and German Ameisensäure. Esters, salts, and the anions derived from formic acid are called formates.


Cyclic dimer of formic acid; dashed green lines represent hydrogen bonds

Formic acid is a colorless liquid having a highly pungent, penetrating odor[5] at room temperature. It is miscible with water and most polar organic solvents, and is somewhat soluble in hydrocarbons. In hydrocarbons and in the vapor phase, it consists of hydrogen-bonded dimers rather than individual molecules.[6][7] Owing to its tendency to hydrogen-bond, gaseous formic acid does not obey the ideal gas law.[7] Solid formic acid (two polymorphs) consists of an effectively endless network of hydrogen-bonded formic acid molecules. This relatively complicated compound also forms a low-boiling azeotrope with water (22.4%) and liquid formic acid also tends to supercool.

Natural occurrence

In nature, it is found in certain ants and in the trichomes of stinging nettle (Urtica dioica).[8] Formic acid is a naturally occurring component of the atmosphere due primarily to forest emissions.


In 2009, the worldwide capacity for producing formic acid was 720,000 tonnes/annum, roughly equally divided between Europe (350,000, mainly in Germany) and Asia (370,000, mainly in China) while production was below 1000 tonnes/annum in all other continents.[9] It is commercially available in solutions of various concentrations between 85 and 99 w/w %.[6] As of 2009, the largest producers are BASF, Eastman Chemical Company, LC Industrial, and Feicheng Acid Chemicals, with the largest production facilities in Ludwigshafen (200,000 tonnes/annum, BASF, Germany), Oulu (105,000, Eastman, Finland), Nakhon Pathom (n/a, LC Industrial) and Feicheng (100,000, Feicheng, China). 2010 prices ranged from around €650/tonne (equivalent to around $800/tonne) in Western Europe to $1250/tonne in the United States.[9]

From methyl formate and formamide

When methanol and carbon monoxide are combined in the presence of a strong base, the result is methyl formate, according to the chemical equation:[6]


In industry, this reaction is performed in the liquid phase at elevated pressure. Typical reaction conditions are 80 °C and 40 atm. The most widely used base is sodium methoxide. Hydrolysis of the methyl formate produces formic acid:


Efficient hydrolysis of methyl formate requires a large excess of water. Some routes proceed indirectly by first treating the methyl formate with ammonia to give formamide, which is then hydrolyzed with sulfuric acid:

HCO2CH3 + NH3 → HC(O)NH2 + CH3OH
2 HC(O)NH2 + 2H2O + H2SO4 → 2HCO2H + (NH4)2SO4

A disadvantage of this approach is the need to dispose of the ammonium sulfate byproduct. This problem has led some manufacturers to develop energy-efficient methods of separating formic acid from the excess water used in direct hydrolysis. In one of these processes (used by BASF) the formic acid is removed from the water by liquid-liquid extraction with an organic base.

Niche chemical routes

By-product of acetic acid production

A significant amount of formic acid is produced as a byproduct in the manufacture of other chemicals. At one time, acetic acid was produced on a large scale by oxidation of alkanes, by a process that cogenerates significant formic acid. This oxidative route to acetic acid is declining in importance, so that the aforementioned dedicated routes to formic acid have become more important.

Hydrogenation of carbon dioxide

The catalytic hydrogenation of CO2 to formic acid has long been studied. This reaction can be conducted homogeneously.[10][11]

Oxidation of biomass

Formic acid can also be obtained by aqueous catalytic partial oxidation of wet biomass (OxFA process).[12][13] A Keggin-type polyoxometalate (H5PV2Mo10O40) is used as the homogeneous catalyst to convert sugars, wood, waste paper or cyanobacteria to formic acid and CO2 as the sole byproduct. Yields of up to 53% formic acid can be achieved.

Laboratory methods

In the laboratory, formic acid can be obtained by heating oxalic acid in glycerol and extraction by steam distillation.[14] Glycerol acts as a catalyst, as the reaction proceeds through a glyceryl oxalate intermediary. If the reaction mixture is heated to higher temperatures, allyl alcohol results. The net reaction is thus:

C2O4H2 → CO2H2 + CO2

Another illustrative method involves the reaction between lead formate and hydrogen sulfide, driven by the formation of lead sulfide.[15]

Pb(HCOO)2 + H2S → 2HCOOH + PbS


Formic acid occurs widely in nature as its conjugate base formate. This anion is produced by reduction of carbon dioxide, catalyzed by the enzyme formate dehydrogenase. An assay for formic acid in body fluids, designed for determination of formate after methanol poisoning, is based on the reaction of formate with bacterial formate dehydrogenase.[16]


A major use of formic acid is as a preservative and antibacterial agent in livestock feed. In Europe, it is applied on silage (including fresh hay) to promote the fermentation of lactic acid and to suppress the formation of butyric acid; it also allows fermentation to occur quickly, and at a lower temperature, reducing the loss of nutritional value.[6] Formic acid arrests certain decay processes and causes the feed to retain its nutritive value longer, and so it is widely used to preserve winter feed for cattle.[17] In the poultry industry, it is sometimes added to feed to kill E. coli bacteria.[18][19] Use as preservative for silage and (other) animal feed constituted 30% of the global consumption in 2009.[9]

Formic acid is also significantly used in the production of leather, including tanning (23% of the global consumption in 2009[9]), and in dyeing and finishing textiles (9% of the global consumption in 2009[9]) because of its acidic nature. Use as a coagulant in the production of rubber[6] consumed 6% of the global production in 2009.[9]

Formic acid is also used in place of mineral acids for various cleaning products,[6] such as limescale remover and toilet bowl cleaner. Some formate esters are artificial flavorings or perfumes. Beekeepers use formic acid as a miticide against the tracheal mite (Acarapis woodi) and the Varroa mite.[20]

Formic acid application has been reported to be an effective treatment for warts.[21]

Formic acid is being investigated for use in fuel cells.[22][23]

Chemical reactions

Formic acid is about 10x stronger than acetic acid. It is used as a volatile pH modifier in HPLC and capillary electrophoresis.

Formic acid is a source for a formyl group for example in the formylation of methylaniline to N-methylformanilide in toluene.[24]

In synthetic organic chemistry, formic acid is often used as a source of hydride ion. The Eschweiler-Clarke reaction and the Leuckart-Wallach reaction are examples of this application. It, or more commonly its azeotrope with triethylamine, is also used as a source of hydrogen in transfer hydrogenation.

The Eschweiler–Clark reaction

As mentioned below, formic acid readily decomposes with concentrated sulfuric acid to form carbon monoxide.

CH2O2 + H2SO4 → H2SO4 + H2O + CO↑


Formic acid shares most of the chemical properties of other carboxylic acids. Because of its high acidity, solutions in alcohols form esters spontaneously. Formic acid shares some of the reducing properties of aldehydes, reducing solutions of gold, silver, and platinum to the metals.[citation needed]


Heat and especially acids cause formic acid to decompose to carbon monoxide (CO) and water (dehydration). Treatment of formic acid with sulfuric acid is a convenient laboratory source of CO.[25][26]

In the presence of platinum, it decomposes with a release of hydrogen and carbon dioxide.

CH2O2 → H2 + CO2

Soluble ruthenium catalysts are also effective.[27][28] Carbon monoxide free hydrogen has been generated in a very wide pressure range (1–600 bar).[27] Formic acid has been considered as a means of hydrogen storage.[29] The co-product of this decomposition, carbon dioxide, can be rehydrogenated back to formic acid in a second step. Formic acid contains 53 g L−1 hydrogen at room temperature and atmospheric pressure, which is three and a half times as much as compressed hydrogen gas can attain at 350 bar pressure (14.7 g L−1). Pure formic acid is a liquid with a flash point of +69 °C, much higher than that of gasoline (−40 °C) or ethanol (+13 °C).

Addition to alkenes

Formic acid is unique among the carboxylic acids in its ability to participate in addition reactions with alkenes. Formic acids and alkenes readily react to form formate esters. In the presence of certain acids, including sulfuric and hydrofluoric acids, however, a variant of the Koch reaction occurs instead, and formic acid adds to the alkene to produce a larger carboxylic acid.[30]

Formic acid anhydride

An unstable formic anhydride, H(C=O)−O−(C=O)H, can be obtained by dehydration of formic acid with N,N'-dicyclohexylcarbodiimide in ether at low temperature.[31]


Some alchemists and naturalists were aware that ant hills give off an acidic vapor as early as the 15th century. The first person to describe the isolation of this substance (by the distillation of large numbers of ants) was the English naturalist John Ray, in 1671.[32][33] Ants secrete the formic acid for attack and defense purposes. Formic acid was first synthesized from hydrocyanic acid by the French chemist Joseph Gay-Lussac. In 1855, another French chemist, Marcellin Berthelot, developed a synthesis from carbon monoxide similar to the process used today.

Formic acid was long considered a chemical compound of only minor interest in the chemical industry. In the late 1960s, however, significant quantities became available as a byproduct of acetic acid production. It now finds increasing use as a preservative and antibacterial in livestock feed.


Formic acid has low toxicity (hence its use as a food additive), with an LD50 of 1.8 g/kg (oral, mice). The concentrated acid is corrosive to the skin.[6]

Formic acid is readily metabolized and eliminated by the body. Nonetheless, it has specific toxic effects; the formic acid and formaldehyde produced as metabolites of methanol are responsible for the optic nerve damage, causing blindness seen in methanol poisoning.[34] Some chronic effects of formic acid exposure have been documented. Some experiments on bacterial species have demonstrated it to be a mutagen.[35] Chronic exposure in humans may cause kidney damage.[35] Another possible effect of chronic exposure is development of a skin allergy that manifests upon re-exposure to the chemical.

Concentrated formic acid slowly decomposes to carbon monoxide and water, leading to pressure buildup in the containing vessel. For this reason, 98% formic acid is shipped in plastic bottles with self-venting caps.

The hazards of solutions of formic acid depend on the concentration. The following table lists the EU classification of formic acid solutions:

Concentration (weight percent)ClassificationR-Phrases
2%–10%Irritant (Xi)R36/38
10%–90%Corrosive (C)R34
>90%Corrosive (C)R35

Formic acid in 85% concentration is flammable, and diluted formic acid is on the U.S. Food and Drug Administration list of food additives.[36] The principal danger from formic acid is from skin or eye contact with the concentrated liquid or vapors. The U.S. OSHA Permissible Exposure Level (PEL) of formic acid vapor in the work environment is 5 parts per million parts of air (ppm).

See also


  1. ^ a b Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. p. 745. ISBN 978-0-85404-182-4. doi:10.1039/9781849733069-FP001. 
  2. ^ a b c d e "NIOSH Pocket Guide to Chemical Hazards #0296". National Institute for Occupational Safety and Health (NIOSH). 
  3. ^ Brown, H. C. et al., in Braude, E. A. and Nachod, F. C., Determination of Organic Structures by Physical Methods, Academic Press, New York, 1955.
  4. ^ a b "Formic acid". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health. 4 December 2014. Retrieved 26 March 2015. 
  5. ^ [1].
  6. ^ a b c d e f g Werner Reutemann and Heinz Kieczka "Formic Acid" in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a12_013
  7. ^ a b Roman M. Balabin (2009). "Polar (Acyclic) Isomer of Formic Acid Dimer: Gas-Phase Raman Spectroscopy Study and Thermodynamic Parameters". J. Phys. Chem. A. 113 (17): 4910–8. PMID 19344174. doi:10.1021/jp9002643. 
  8. ^ Hoffman, Donald R. "Ant venoms" Current Opinion in Allergy and Clinical Immunology 2010, vol. 10, pages 342–346. doi:10.1097/ACI.0b013e328339f325
  9. ^ a b c d e f S. N. Bizzari; M. Blagoev (June 2010). "CEH Marketing Research Report: FORMIC ACID". Chemical Economics Handbook. SRI consulting. Retrieved July 2011.  Check date values in: |access-date= (help)
  10. ^ P. G. Jessop, in Handbook of Homogeneous Hydrogenation (Eds.: J. G. de Vries, C. J. Elsevier), Wiley-VCH, Weinheim, Germany, 2007, pp. 489–511.
  11. ^ P. G. Jessop; F. Joó; C.-C. Tai (2004). "Recent advances in the homogeneous hydrogenation of carbon dioxide". Coord. Chem. Rev. 248 (21–24): 2425. doi:10.1016/j.ccr.2004.05.019. 
  12. ^ R. Wölfel; N. Taccardi; A. Bösmann; P. Wasserscheid (2011). "Selective catalytic conversion of biobased carbohydrates to formic acid using molecular oxygen". Green Chem. (13): 2759. doi:10.1039/C1GC15434F. 
  13. ^ J. Albert; R. Wölfel; A. Bösmann; P. Wasserscheid (2012). "Selective oxidation of complex, water-insoluble biomass to formic acid using additives as reaction accelerators". Energy Environ. Sci. (5): 7956. doi:10.1039/C2EE21428H. 
  14. ^ Chattaway, F. D. (1914). "Interaction of glycerol and oxalic acid". Journal of the Chemical Society, Transactions. 105: 151–156. doi:10.1039/CT9140500151.  Available at HathiTrust.
  15. ^ Arthur Sutcliffe (1930) Practical Chemistry for Advanced Students (1949 Ed.), John Murray, London.
  16. ^ Makar AB, McMartin KE, Palese M, Tephly TR; McMartin; Palese; Tephly (1975). "Formate assay in body fluids: application in methanol poisoning". Biochem Med. 13 (2): 117–26. PMID 1. doi:10.1016/0006-2944(75)90147-7. 
  17. ^ Organic Acids and Food Preservation, Maria M. Theron, J. F. Rykers Lues
  18. ^ Griggs, J. P.; J (2005). "Alternatives to Antibiotics for Organic Poultry Production". The Journal of Applied Poultry Research. 14 (4): 750. doi:10.1093/japr/14.4.750. 
  19. ^ Garcia, V.; Catala-Gregori, P.; Hernandez, F.; Megias, M. D.; Madrid, J. (2007). "Effect of Formic Acid and Plant Extracts on Growth, Nutrient Digestibility, Intestine Mucosa Morphology, and Meat Yield of Broilers". The Journal of Applied Poultry Research. 16 (4): 555. doi:10.3382/japr.2006-00116. 
  20. ^
  21. ^ Bhat RM, Vidya K, Kamath G; Vidya; Kamath (June 2001). "Topical formic acid puncture technique for the treatment of common warts". International Journal of Dermatology. 40 (6): 415–9. PMID 11589750. doi:10.1046/j.1365-4362.2001.01242.x. 
  22. ^ Ha, S.; Larsen, R.; Masel, R. I. (2005). "Performance characterization of Pd/C nanocatalyst for direct formic acid fuel cells". Journal of Power Sources. 144 (1): 28–34. doi:10.1016/j.jpowsour.2004.12.031. 
  23. ^ Jorn Madslien (27 June 2017). "Ant power: Take a ride on a bus that runs on formic acid". BBC News. Retrieved 11 July 2017. 
  24. ^ L. F. Fieser; J. E. Jones (1955). "N-Methylformanilide". Org. Synth. ; Coll. Vol., 3, p. 590 
  25. ^ Koch, H.; Haaf, W. (1973). "1-Adamantanecarboxylic Acid". Org. Synth. ; Coll. Vol., 5, p. 20 
  26. ^ G. H. Coleman, David Craig (1943). "p-Tolualdehyde". Org. Synth. ; Coll. Vol., 2, p. 583 
  27. ^ a b C. Fellay, P. J. Dyson, G. Laurenczy; Dyson; Laurenczy (2008). "A Viable Hydrogen-Storage System Based On Selective Formic Acid Decomposition with a Ruthenium Catalyst". Angew. Chem. Int. Ed. 47 (21): 3966–3970. PMID 18393267. doi:10.1002/anie.200800320. 
  28. ^ G. Laurenczy, C. Fellay, P. J. Dyson, Hydrogen production from formic acid. PCT Int. Appl. (2008), 36pp. CODEN: PIXXD2 WO 2008047312 A1 20080424 AN 2008:502691
  29. ^ Joó, Ferenc (2008). "Breakthroughs in Hydrogen Storage-Formic Acid as a Sustainable Storage Material for Hydrogen". ChemSusChem. 1 (10): 805–8. PMID 18781551. doi:10.1002/cssc.200800133. 
  30. ^ Haaf, Wolfgang (1966). "Die Synthese sekundärer Carbonsäuren nach der Ameisensäure-Methode". Chemische Berichte. 99 (4): 1149–1152. doi:10.1002/cber.19660990410. 
  31. ^ Wu, G.; Shlykov, S.; Alseny, F. S. Van; Geise, H. J.; Sluyts, E.; Van der Veken, B. J. (1995). "Formic Anhydride in the Gas Phase, Studied by Electron Diffraction and Microwave and Infrared Spectroscopy, Supplemented with Ab-Initio Calculations of Geometries and Force Fields". J. Phys. Chem. 99 (21): 8589–8598. doi:10.1021/j100021a022. 
  32. ^ Wray, J. (1670). "Extract of a Letter, Written by Mr. John Wray to the Publisher January 13. 1670. Concerning Some Un-Common Observations and Experiments Made with an Acid Juyce to be Found in Ants". Philosophical Transactions of the Royal Society of London. 5 (57–68): 2063. doi:10.1098/rstl.1670.0052. 
  33. ^ Johnson, W. B. (1803). History of the process and present state of animal chemistry. 
  34. ^ Sadun AA (2002). "Mitochondrial optic neuropathies". J. Neurol. Neurosurg. Psychiatr. 72 (4): 423–5. PMC 1737836Freely accessible. PMID 11909893. doi:10.1136/jnnp.72.4.423. 
  35. ^ a b "Occupational Safety and Health Guideline for Formic Acid". OSHA. Retrieved 28 May 2011. 
  36. ^ U.S. Code of Federal Regulations: 21 CFR 186.1316, 21 CFR 172.515

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