PROPERTIES OF FORMIC ACID

Formic acid is miscible with water and most polar organic solvents, and somewhat soluble in hydrocarbons. In hydrocarbons and in the vapor phase, it actually consists of hydrogen-bonded dimers rather than individual molecules. In the gas phase, this hydrogen-bonding results in severe deviations from the ideal gas law. Liquid and solid formic acid consists of an effectively infinite network of hydrogen-bonded formic acid molecules.

Formic acid shares most of the chemical properties of other carboxylic acids, although under normal conditions it will not form either an acyl chloride or an acid anhydride. Until very recently, all attempts to form either of these derivatives have resulted in carbon monoxide instead. It has now been shown that the anhydride may be produced by reaction of formyl fluoride with sodium formate at −78°C, and the chloride by passing HCl into a solution of 1-formimidazole in monochloromethane at −60°C[1]. Heat can also cause formic acid to decompose to carbon monoxide and water. Formic acid shares some of the reducing properties of aldehydes.

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 takes place instead, and formic acid adds to the alkene to produce a larger carboxylic acid.Most simple formate salts are water-soluble. It is also a bi-functional compound.

USAGE OF FORMIC ACID

The principal use of formic acid is as a preservative and antibacterial agent in livestock feed. When sprayed on fresh hay or other silage, it 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 salmonella bacteria.
Other uses:

• It is used to process organic latex (sap) into raw rubber.
• Beekeepers use formic acid as a miticide against the Varroa mite.
• It is of minor importance in the textile industry and for the tanning of leather.
• Some formate esters are artificial flavorings or perfumes.
• It is the active ingredient in some brands of household lime scale remover.
• It is used in laboratories as a solvent modifier for HPLC separations of proteins and peptides, especially when the sample is being prepared for mass spectrometry analysis.

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 is also used as a source of hydrogen in transfer hydrogenation.