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Formic Acid

Formic Acid

Gist

Formic acid is the simplest carboxylic acid, containing a single carbon. Occurs naturally in various sources including the venom of bee and ant stings, and is a useful organic synthetic reagent. Principally used as a preservative and antibacterial agent in livestock feed.

Summary

Formic acid (HCO2H) is the simplest of the carboxylic acids, used in processing textiles and leather. Formic acid was first isolated from certain ants and was named after the Latin formica, meaning “ant.” It is made by the action of sulfuric acid upon sodium formate, which is produced from carbon monoxide and sodium hydroxide.

Formic acid is also prepared in the form of its esters by treatment of carbon monoxide with an alcohol such as methanol (methyl alcohol) in the presence of a catalyst.

Formic acid is not a typical carboxylic acid; it is distinguished by its acid strength, its failure to form an anhydride, and its reactivity as a reducing agent—a property due to the ―CHO group, which imparts some of the character of an aldehyde. The methyl and ethyl esters of formic acid are commercially produced. Concentrated sulfuric acid dehydrates formic acid to carbon monoxide.

Pure formic acid is a colourless, fuming liquid with a pungent odour; it irritates the mucous membranes and blisters the skin. It freezes at 8.4 °C (47.1 °F) and boils at 100.7 °C (213.3 °F).

Details

Formic acid (from Latin formica 'ant'), systematically named methanoic acid, is the simplest carboxylic acid, and has the chemical formula HCOOH and structure H−C(=O)−O−H. It is an important intermediate in chemical synthesis and occurs naturally, most notably in some ants. Esters, salts and the anion derived from formic acid are called formates. Industrially, formic acid is produced from methanol.

Natural occurrence

Formic acid is found naturally in insects, weeds, fruits and vegetables, and forest emissions. It appears in most ants and in stingless bees of the genus Oxytrigona. Wood ants from the genus Formica can spray formic acid on their prey or to defend the nest. The puss moth caterpillar (Cerura vinula) will spray it as well when threatened by predators. It is also found in the trichomes of stinging nettle (Urtica dioica). Apart from that, this acid is incorporated in many fruits such as pineapple (0.21 mg per 100 g), apple (2 mg per 100 g) and kiwi (1 mg per 100 g), as well as in many vegetables, namely onion (45 mg per 100 g), eggplant (1.34 mg per 100 g) and, in extremely low concentrations, cucumber (0.11 mg per 100 g). Formic acid is a naturally occurring component of the atmosphere primarily due to forest emissions.

History

As early as the 15th century, some alchemists and naturalists were aware that ant hills give off an acidic vapor. 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. 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, significant quantities became available as a byproduct of acetic acid production. It now finds increasing use as a preservative and antibacterial in livestock feed.

Properties

Formic acid is a colorless liquid having a pungent, penetrating odor at room temperature, comparable to the related acetic acid. Formic acid is about ten times stronger than 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. Owing to its tendency to hydrogen-bond, gaseous formic acid does not obey the ideal gas law. Solid formic acid, which can exist in either of two polymorphs, consists of an effectively endless network of hydrogen-bonded formic acid molecules. Formic acid forms a high-boiling azeotrope with water (107.3 °C; 77.5% formic acid). Liquid formic acid tends to supercool.

Chemical formula  :  CH2O2
Molar mass  :  46.025 g·{mol}^{-1}
Appearance  :  Colorless fuming liquid
Odor  :  Pungent, penetrating
Density  :  1.220 g/mL
Melting point  :  8.4 °C (47.1 °F; 281.5 K)
Boiling point  :  100.8 °C (213.4 °F; 373.9 K)
Solubility in water  :  Miscible
Solubility  :  Miscible with ether, acetone, ethyl acetate, glycerol, methanol, ethanol;
Partially soluble in benzene, toluene, xylenes.

Additional Information

Formic acid is the simplest carboxylic acid. Its discovery in the distillation products of ants is usually attributed to English scientist John Gray in 1671, although there is evidence that a Samuel Fisher made the discovery the year before. The name “formic” comes from formica1, the Latin word for ant and the name of the genus to which many ants belong.

Although ants and other insects produce significant amounts of formic acid, the large worldwide production of the chemical (870 kt in 2021) is made industrially. Most of it is made from carbon monoxide, either by heating it with sodium hydroxide to produce sodium formate, which is then acidified, or via the base-catalyzed reaction of CO and methanol to make methyl formate, which is hydrolyzed to the acid. Formic acid is also a major byproduct of acetic acid manufacture.

Formic acid has a wide range of uses: in leather tanning, as a decalcifier and cleaning product, as a chemical reducing agent, as a preservative in animal feeds, and for manufacturing its salts and esters. Its synthetic method can also be reversed to liberate CO.

This is Earth Week, and this year chemists and students are celebrating it by learning about insect chemistry. Foremost among insect-produced chemicals, formic acid is produced by ants in the subfamily Formicinae (almost 300 species) and some bee species as a venom against predators and as a pheromone to warn fellow insects of danger. Ants in the Formica genus emit formic acid when they bite or spray, causing skin irritation or worse in humans. Fire ants (Solenopsis spp.) cause even more damage because their venom contains toxic alkaloids.

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