Formic acid, systematically named methanol acid, is the simplest carboxylic acid with the chemical formula HCOOH and the structure H-C (=O) - O-H. It is an important chemical synthesis intermediate that naturally exists, especially in some ants. The esters, salts, and anions generated by formic acid are called formates. In industry, formic acid is produced from methanol.

In nature, formic acid is present in most ants and stingless bees of the genus Apis. Wood ants from the wood ant genus can spray formic acid on their prey or protect their nests. When threatened by predators, the cat moth caterpillar (Cerura vinula) also sprays it. It also exists in the hair of nettles (nettles). In addition, this acid is also present in many fruits such as pineapples (0.21 milligrams per 100 grams), apples (2 milligrams per 100 grams), and kiwifruit (1 milligram per 100 grams), as well as many vegetables such as onions (45 milligrams per 100 grams), eggplants (1.34 milligrams per 100 grams), and extremely low concentrations of cucumbers (0.11 milligrams per 100 grams). Formic acid is a naturally occurring component in the atmosphere, mainly caused by forest emissions.

As early as the 15th century, some alchemists and naturalists realized that the ant mound would release an acid vapor. In 1671, the British naturalist John Ray first described the separation of this substance (by distillation of a large number of ants). Ants secrete formic acid for attack and defense. Formic acid was first synthesized from hydrocyanic acid by French chemist Joseph G é - L ü sack. In 1855, another French chemist, Marcelin Berthelot, invented a method for synthesizing carbon monoxide, similar to the method used today.

Formic acid has long been considered an insignificant compound in the chemical industry. However, in the late 1960s, as a byproduct of acetic acid production, a large amount of benzoic acid became possible. It is increasingly used as a preservative and antibacterial agent in livestock feed.

Formic acid is a colorless liquid with a pungent penetrating odor at room temperature, equivalent to related acetic acid. The strength of formic acid is about ten times that of acetic acid.

It is miscible with water and most polar organic solvents, and to some extent soluble in hydrocarbons. In hydrocarbons and gas phases, it is composed of hydrogen bonded dimers rather than individual molecules. Because of the hydrogen bonding tendency of formic acid, gaseous formic acid does not obey the ideal gas law. Solid formic acid can exist in either of two polycrystalline states, consisting of an effective and endless network of hydrogen bonded formic acid molecules. Formic acid forms a high boiling point azeotrope with water (22.4%). Liquid formic acid is prone to overcooling.