Formic Acid
Formic acid belongs to the family of carboxylic acids and has the chemical formula HCOOH or HCO2H. The carbon atom has a double bond with one of the oxygen atoms. It is the simplest carboxylic acid and has the lowest molecular weight (46.03). A colorless, corrosive liquid with a sharp odor, formic acid boils at 213.3°F (100.7°C) and solidifies at 47.1°F (8.4°C). Like other acids, it reacts with most alcohols to form esters and decomposes when heated; it is also easily oxidized.
Formic acid decomposes slowly at room temperature into carbon monoxide (CO) and Water (H2O). Decomposition is dependent on temperature and concentration. Though it is neither explosive nor spontaneously flammable in air, formic acid is flammable under certain conditions and is corrosive. It is also considered an environmental contaminant of air and water and has been identified as the toxic intermediate (formate) in methanol poisoning.
Formic acid occurs naturally in a variety of plants and fruits (the fruit of the soaptree), mammalian tissues, and insect venoms, including the bodies of red ants and the stingers of bees. It occurs synthetically as a byproduct in the manufacture of acetaldehyde and formaldehyde and during the atmospheric oxidation of turpentine. Formic acid is prepared commercially by heating carbon monoxide and sodium hydroxide to form sodium formate. The sodium formate is then carefully treated with sulfuric acid at low temperatures and distilled in a vacuum to yield formic acid. Another preparation method involves acid hydrolysis of methyl formate.
A single-step low-cost method has also been developed at the Boreskov Institute of Catalysis to produce formic acid with a yield of 90%. This method, claimed to be the first single stage method to produce formic acid from formaldehyde-containing gases, involves direct oxidation of formaldehyde by oxygen over an original oxide catalyst in a tube fixed-bed reactor followed by the product condensation. The final product contains 55-85% of formic acid depending on the raw material type and no more than 0.1% of organic admixtures.Distillation can increase the content of formic acid up to 95% and higher.
Formic acid has a wide range of industrial uses and over 300,000 tons is produced on a global basis every year. As an intermediate, it is used as a solvent for polyamides and cellulose acetate and in the manufacture of various chemicals and pharmaceuticals, such as caffeine, enzymes, antibiotics, artificial sweeteners, polyvinyl chloride plasticizers, and rubber antioxidants. In the dyeing of natural and synthetic fibers, formic acid regulates the pH and is also used to help impregnate waterproof textiles. Formic acid is also used in the preservation of green feed/fodder and in the coagulation of natural rubber (latex).
In addition, formic acid is an active ingredient in commercial cleaning products, such as descalers, rust removers, and degreasers. Due to its bactericidal properties, formic acid is used in the disinfection of the wood barrels used for storing wine and beer. A more recent application of formic acid is for pH regulation of flue gas desulfurization. The flue gas is passed through an aqueous limestone slurry containing formic acid. The sulfur dioxide in the gas reacts with the limestone to form gypsum (calcium sulfate). Formic acid is also used in fumigants, refrigerants, solvents for perfumes and lacquers, brewing, and silvering glass.
In 1998, a pesticide based on formic acid was developed by the U.S. Department of Agriculture as an alternative way to save beehives from varroa mites, pests that are becoming resistant to the conventional pesticide, fluvalinate. Since the formic acid is applied as a gel, it is safer to use than the formic acid spray employed in Europe. In field tests, the formic acid gel killed up to 84% of varroa mites and 100% of tracheal mites, another bee pest.
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