Formic acid, systematically 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. Esters, salts, and the anion derived from formic acid are called formates. Industrially formic acid is produced from methanol.

1    Properties
2    Natural occurrence
3    Production
3.1    From methyl formate and formamide
3.2    Niche chemical routes
3.2.1    By-product of acetic acid production
3.2.2    Hydrogenation of carbon dioxide
3.2.3    Oxidation of biomass
3.2.4    Laboratory methods
3.3    Biosynthesis
4    Uses
5    Chemical reactions
6    Reactions
6.1    Decomposition
6.2    Addition to alkenes
6.3    Formic acid anhydride
7    History
8    Safety
9    See also
10    References
11    External links

Cyclic dimer of formic acid; dashed green lines represent hydrogen bonds
Formic acid is a colorless liquid having a pungent, penetrating odor[5] at room temperature, not unlike the related acetic acid. 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
See also: Insect defenses
In nature, formic acid is found in most ants and in stingless bees of the Oxytrigona genus.[8][9] The wood ants from the genus Formica can spray formic acid on their prey or to defend the nest. It is also found in the trichomes of stinging nettle (Urtica dioica). Formic acid is a naturally occurring component of the atmosphere due primarily to forest emissions.[10]

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.[11] 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.[11]

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.[citation needed]

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.[12][13]

Oxidation of biomass
Formic acid can also be obtained by aqueous catalytic partial oxidation of wet biomass (OxFA process).[14][15] 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.[16] 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.[17]

Pb(HCOO)2 + H2S → 2HCOOH + PbS
Formic acid is named after ants which have high concentrations of the compound in their venom. In ants formic acid is derived from serine through a 5,10-Methenyltetrahydrofolate intermediate.[18] The conjugate base of formic acid, formate, also occurs widely in nature. 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.[19]

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.[20] In the poultry industry, it is sometimes added to feed to kill E. coli bacteria.[21][22] Use as preservative for silage and (other) animal feed constituted 30% of the global consumption in 2009.[11]

Formic acid is also significantly used in the production of leather, including tanning (23% of the global consumption in 2009[11]), and in dyeing and finishing textiles (9% of the global consumption in 2009[11]) because of its acidic nature. Use as a coagulant in the production of rubber[6] consumed 6% of the global production in 2009.[11]