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Formic acid

2007 Schools Wikipedia Selection. Related subjects: Chemical compounds

                                                               Formic acid
                 Skeletal structure of formic acid 3D model of formic acid
                                                                   General
                                            Systematic name methanoic acid
                                                   Other names formic acid
                                                  hydrogen carboxylic acid
                                                               aminic acid
                                               Molecular formula CH[2]O[2]
                                                                     HCOOH
                                                               SMILES O=CO
                                                  Molar mass 46.0254 g/mol
                                      Appearance colourless, fuming liquid
                                                      CAS number [64-18-6]
                                                                Properties
                                     Density and phase 1.22 g/cm³, liquid
                                              Solubility in water miscible
                                            Melting point 8.4°C (281.5 K)
                                          Boiling point 100.8°C (373.9 K)
                                                      Acidity (pK[a]) 3.75
                                               Viscosity 1.57 c P at 26°C
                                                                 Structure
                                                    Molecular shape Planar
                                                 Dipole moment 1.41 D(gas)
                                                                   Hazards
                                                        MSDS External MSDS
                                                    Main hazards Corrosive
                                                                  NFPA 704

   2
   2
   1

                                                         Flash point 69°C
                                                        R-phrases R10, R35
                                             S-phrases S1/2, S23, S26, S45
                                                    RTECS number LQ4900000
                                                   Supplementary data page
                                     Structure & properties n, ε[r], etc.
                                        Thermodynamic data Phase behaviour
                                                        Solid, liquid, gas
                                             Spectral data UV, IR, NMR, MS
                                                         Related compounds
                                      Related carboxylic acids acetic acid
                                                            propionic acid
                                            Related compounds formaldehyde
                                                                  methanol
                          Except where noted otherwise, data are given for
                     materials in their standard state (at 25°C, 100 kPa)
                                         Infobox disclaimer and references

   Formic acid (systematically called methanoic acid) is the simplest
   carboxylic acid. Its formula is CH[2]O[2] or HCOOH.

   In nature, it is found in the stings and bites of many insects of the
   order Hymenoptera, including bees and ants. It is also a significant
   combustion product resulting from alternative fueled vehicles burning
   methanol (and ethanol, if contaminated with water) when mixed with
   gasoline. Its name comes from the Latin word for ant, formica,
   referring to its early isolation by the distillation of ant bodies. A
   chemical compound such as a salt from the neutralization of formic acid
   with a base, or an ester derived from formic acid, is referred to as
   formate (or methanoate). The formate ion has the formula HCOO^−.

Properties

   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^. 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.

History

   As early as the 15th century, some alchemists and naturalists were
   aware that ant hills gave off an acidic vapor. The first person to
   describe the isolation of this substance (by the distillation of large
   numbers of dead 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 that is similar
   to that used today.

   In the chemical industry, formic acid was long considered a chemical
   compound of only minor industrial interest. In the late-1960s, however,
   significant quantities of it became available as a byproduct of acetic
   acid production. It now finds increasing use as a preservative and
   antibacterial in livestock feed.

Production

   A significant amount of formic acid is produced as a byproduct in the
   manufacture of other chemicals, especially acetic acid. This production
   is insufficient to meet the present demand for formic acid, and some
   formic acid must be produced for its own sake.

   When methanol and carbon monoxide are combined in the presence of a
   strong base, the formic acid derivative methyl formate results,
   according to the chemical equation

          CH[3]OH + CO → HCOOCH[3]

   In industry, this reaction is performed in the liquid phase at elevated
   pressure. Typical reaction conditions are 80°C and 40 atm. The most
   widely-used base is sodium methoxide. Hydrolysis of the methyl formate
   produces formic acid:

          HCOOCH[3] + H[2]O → HCOOH + CH[3]OH

   Direct hydrolysis of methanol requires a large excess of water to
   proceed efficiently, and some producers perform it by an indirect route
   by first reacting the methyl formate with ammonia to produce formamide,
   and then hydrolyzing the formamide with sulfuric acid to produce formic
   acid:

          HCOOCH[3] + NH[3] → HCONH[2] + CH[3]OH
          HCONH[2] + H[2]O + ½H[2]SO[4] → HCOOH + ½ (NH[4])[2]SO[4]

   This technique has problems of its own, particularly disposing of the
   ammonium sulfate byproduct, so some manufacturers have recently
   developed energy efficient means of separating formic acid from the
   large excess amount of water used in direct hydrolysis. In one of these
   processes (used by BASF) the formic acid is removed from the water via
   liquid extraction with an organic base.

   In the laboratory formic acid can be obtained by heating oxalic acid in
   anhydrous glycerol and extraction by steam distillation. Another
   preparation (which must be performed under a fume hood) is the acid
   hydrolysis of ethyl isonitrile using HCl solution.

                C[2]H[5]NC + 2H[2]O → C[2]H[5]NH[2] + HCOOH

   The isonitrile being obtained by reacting ethyl amine with chloroform
   (note that the fume hood is required because of the overpoweringly
   objectionable odour of the isonitrile).

Uses

   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 limescale
       remover.

   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.

   In the laboratory formic acid is also used as source for carbon
   monoxide, which is set free by the addition of sulfuric acid. Formic
   acid is also a source for a formyl group for example in the formylation
   of metylaniline to N-methylformanilide in toluene.

   Fuel cells that use modified formic acid are promising.

Safety

   The principal danger from formic acid is from skin or eye contact with
   liquid formic acid or with the concentrated vapors. Any of these
   exposure routes can cause severe chemical burns, and eye exposure can
   result in permanent eye damage. Inhaled vapors may similarly cause
   irritation or burns in the respiratory tract. Since carbon monoxide may
   be also be present in formic acid vapors, care should be taken wherever
   large quantities of formic acid fumes are present. The US OSHA
   Permissible Exposure Level ( PEL) of formic acid vapor in the work
   environment is 5 parts per million parts of air ( ppm).

   Formic acid is readily metabolized and eliminated by the body.
   Nonetheless, some chronic effects have been documented. Some animal
   experiments have demonstrated it to be a mutagen, and chronic exposure
   may cause liver or kidney damage. Another possibility with chronic
   exposure is development of a skin allergy that manifests upon
   re-exposure to the chemical.

   The hazards of solutions of formic acid depend on the concentration.
   The following table lists the EU classification of formic acid
   solutions:
   Safety symbol
   Enlarge
   Safety symbol
   Concentration
   by weight    Classification R-Phrases
   2%–10%       Irritant (Xi)  R36/38
   10%–90%      Corrosive (C)  R34
   >90%         Corrosive (C)  R35

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