Formic acid


Formic acid (also called methanoic acid) is the simplest carboxylic acid. Its chemical formula is HCOOH or HCO2H. It is an important intermediate in chemical synthesis and occurs naturally, most notably in ant venom. In fact, its name 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 referred to as formates.

Formic acid is a colourless liquid having a highly pungent, penetrating odour at room temperature. It is miscible with water and most polar organic solvents, and is somewhat soluble in hydrocarbons. In hydrocarbons and in the vapour phase, it consists of hydrogen-bonded dimers rather than individual molecules. Owing to its tendency to hydrogen-bond, gaseous formic acid does not obey the ideal gas law. 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.



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

Formic acid is also significantly used in the production of leather, including tanning and in dyeing and finishing of textile because of its acidic nature and also used as a coagulant in the production of rubber.

Furthermore, formic acid is used instead of mineral acids for various cleaning products, such as limescale remover and toilet bowl cleaner. Some formate esters are artificial flavourings or perfumes. Beekeepers use formic acid as a miticide against the tracheal mite (Acarapis woodi) and the Varroa mite. The use of formic acid in fuel cells is also under investigation.

Shipment / Storage

Properties of formic acid
Flash point            :    69°C (156°F)
Temperature         :    601°C
Explosive limits     :    14–34%
LD50                     :    700 mg/kg (rat, oral)
Melting point         :    8.4°C
Boiling point          :    100.8°C
Solubility in water  :    miscible
Solubility                :    miscible with ether, acetone, ethyl acetate, glycerol, methanol, ethanol, partially soluble in benzene, toluene, xylenes.

For overseas carriage aspects of chemicals, the readers are recommended to acquire or have access to a good chemical dictionary, and a copy of the International Maritime Dangerous Goods (IMDG) Code, issued by the International Maritime Organisation. Also consult the applicable MSDS sheet.

Risk factors

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, however, corrosive to the skin.

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 optic nerve damage, causing blindness as seen in methanol poisoning. Some chronic effects of formic acid exposure have been documented. Some experiments on bacterial species have demonstrated it to be a mutagen. Chronic exposure to humans may cause kidney damage. Another 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 container it is kept in. 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.

Formic acid in 85% concentration is not flammable, and diluted formic acid is on the U.S. Food and Drug Administration list of food additives. The principal danger from formic acid is from skin or eye contact with the concentrated liquid or vapours.