Formic acid

Formic acid
IUPAC name
Methanoic acid
Other names
Formic acid
Hydrogen carboxylic acid
Formylic acid
Aminic acid
Identifiers
CAS number 64-18-6 YesY
PubChem 284
ChemSpider 278
ChEBI 30751
RTECS number LQ4900000
ATCvet code QP53AG01
Properties
Molecular formula CH2O2
Molar mass 46.03 g mol−1
Appearance Colorless, fuming liquid
Density 1.22 g/mL, liquid
Melting point

8.4 °C, 282 K, 47 °F
Boiling point

101 °C, 374 K, 214 °F
Solubility in water Miscible
Acidity (pKa) 3.744
Viscosity 1.57 cP at 26 °C
Structure
Molecular shape Planar
Dipole moment 1.41 D(gas)
Hazards
MSDS JT Baker
R-phrases R10 R35
S-phrases (S1/2) S23 S26 S45
NFPA 704
NFPA 704.svg
2
3
1
Flash point 69 °C (156 °F)
Related compounds
Related carboxylic acids Acetic acid
Propionic acid
Related compounds Formaldehyde
Methanol
 YesY (what is this?)  (verify)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Formic acid (also called methanoic acid) is the simplest carboxylic acid. Its formula is HCOOH or HCO2H. It is an important intermediate in chemical synthesis and occurs naturally, most notably in the venom of bee and ant stings. In fact, its name comes from the Latin word for ant, formica, referring to its early isolation by the distillation of ant bodies. Esters, salts, and the anion derived from formic acid are referred to as formate(s).

Contents

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 consists of hydrogen-bonded dimers rather than individual molecules.[1][2] Owing to its tendency to hydrogen-bond, gaseous formic acid does not obey the ideal gas law.[2] Solid formic acid (two polymorphs) consists of an effectively endless network of hydrogen-bonded formic acid molecules. This relatively complicated compound also forms a low-boiling azeotrope with water (22.4%) and liquid formic acid also tends to supercool.

Reactions

Formic acid shares most of the chemical properties of other carboxylic acids. Reflecting its high acidity, its solutions in alcohols form esters spontaneously. Formic acid shares some of the reducing properties of aldehydes, reducing solutions of gold, silver, and platinum to the metals.

Decomposition

Heat and especially acids cause formic acid to decompose to carbon monoxide (CO) and water(dehydration). Treatment of formic acid with sulfuric acid is a convenient laboratory source of CO.

In the presence of platinum, it decomposes with a release of hydrogen and carbon dioxide. Soluble ruthenium catalysts are also effective.[3][4] Carbon monoxide free hydrogen has been generated in a very wide pressure range (1-600 bar). Formic acid has even been considered as a material for hydrogen storage.[5] The co-product of this decomposition, carbon dioxide, can be rehydrogenated back to formic acid in a second step. Formic acid contains 53 g L−1 hydrogen at room temperature and atmospheric pressure, which is twice as much as compressed hydrogen gas can attain at 350 bar pressure. Pure formic acid is a liquid with a flash point - ignition temperature of + 69 °C, much higher than that of gasoline (– 40 °C) or ethanol (+ 13 °C).

Addition to alkenes

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 occurs instead, and formic acid adds to the alkene to produce a larger carboxylic acid.

Formic acid anhydride

The reaction of formyl fluoride with sodium formate affords formic anhydride. The other three methods involved the use of dehydrating agents. The formic anhydride, however, is stable only in ethereal solution and decomposes upon attempted distillation.[6]

Production

From methyl formate and formamide

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:[1]

CH3OH + CO → HCO2CH3

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:

HCO2CH3 + H2O → HCO2H + CH3OH

Efficient hydrolysis of methyl formate requires a large excess of water. Some routes proceed indirectly by first treating the methyl formate with ammonia to give formamide, which is then hydrolyzed with sulfuric acid:

HCO2CH3 + NH3 → HC(O)NH2 + CH3OH
2 HC(O)NH2 + 2 H2O + H2SO4 → 2HCO2H + (NH4)2SO4

This approach suffers from the need to dispose of the ammonium sulfate byproduct. This problem has led some manufacturers to develop energy efficient means for 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-liquid extraction with an organic base.

By-product of acetic acid production

A significant amount of formic acid is produced as a byproduct in the manufacture of other chemicals. At one time, acetic acid was produced on a large scale by oxidation of alkanes, via a process that cogenerates significant formic acid. This oxidative route to acetic acid is declining in importance, so that the aforementioned dedicated routes to formic acid have become more important.

Hydrogenation of carbon dioxide

The catalytic hydrogenation of CO2 has long been studied. This reaction can be conducted homogeneously.[7][8]

Laboratory methods

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 (C2H5NC) using HCl solution.[9]

C2H5NC + 2 H2O → C2H5NH2 + HCO2H

The isonitrile can be obtained by reacting ethyl amine with chloroform (note that the fume hood is required because of the overpoweringly objectionable odor 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.

Reagent in organic chemistry

Formic acid is a source for a formyl group for example in the formylation of methylaniline to N-methylformanilide in toluene.[10] 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 or more commonly its azeotrope with triethylamine, is also used as a source of hydrogen in transfer hydrogenation.

Other uses

History

Some alchemists and naturalists were aware that ant hills give off an acidic vapor as early as the 15th century. 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 that is similar to that used today.

Formic acid was long considered a chemical compound of only minor industrial interest in the chemical industry. 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.

In nature

In nature, it is found in the stings and bites of many insects of the order Hymenoptera, mainly ants, and is also present in stinging nettles. Because of its abundance in their diet, giant anteaters (unlike most mammals) do not produce hydrochloric acid for their gastric acid.[11]

Safety

Formic acid in 85% concentration is not flammable, and diluted formic acid is on the US Food and Drug Administration list of food additives.[12] The principal danger from formic acid is from skin or eye contact with the concentrated liquid or vapors. 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, it has specific toxic effects; the formic acid and formaldehyde produced as metabolites of methanol are responsible for the optic nerve damage, causing blindness seen in methanol poisoning.[13] Some chronic effects of formic acid exposure have been documented. Some animal experiments have demonstrated it to be a mutagen, and chronic exposure may cause liver or kidney damage. Another affect of chronic exposure is development of a skin allergy that manifests upon re-exposure to the chemical.

Concentrated formic acid slowly decomposes to carbon monoxide and water, leading to pressure buildup in the container it is kept in. For this reason, 98% formic acid is shipped in plastic bottles with self-venting caps.

The hazards of solutions of formic acid depend on the concentration. The following table lists the EU classification of formic acid solutions:

Concentration (weight percent) Classification R-Phrases
2%–10% Irritant (Xi) R36/38
10%–90% Corrosive (C) R34
>90% Corrosive (C) R35

An assay for formic acid in body fluids, designed for determination of formate after methanol poisoning, is based on the reaction of formate with bacterial formate dehydrogenase.[14]

References

  1. ↑ 1.0 1.1 Werner Reutemann and Heinz Kieczka “Formic Acid” in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a12_013
  2. ↑ 2.0 2.1 Roman M. Balabin (2009). "Polar (Acyclic) Isomer of Formic Acid Dimer: Gas-Phase Raman Spectroscopy Study and Thermodynamic Parameters". J. Phys. Chem. A 113 (17): 4910. doi:10.1021/jp9002643. PMID 19344174. 
  3. ↑ C. Fellay, P. J. Dyson, G. Laurenczy, A Viable Hydrogen-Storage System Based On Selective Formic Acid Decomposition with a Ruthenium Catalyst, Angew. Chem. Int. Ed., 2008, 47, 3966–3970.
  4. ↑ G. Laurenczy, C. Fellay, P. J. Dyson, Hydrogen production from formic acid. PCT Int. Appl. (2008), 36pp. CODEN: PIXXD2 WO 2008047312 A1 20080424 AN 2008:502691
  5. ↑ F. Joó, Breakthroughs in Hydrogen Storage – Formic Acid as a Sustainable Storage Material for Hydrogen, ChemSusChem 2008, 1, 805–808.
  6. ↑ George A. Olah; Yashwant D. Vankar; Massoud Arvanaghi; Jean Sommer (1979). "Formic Anhydride". Angew. Chem. Int. Ed. Engl. 18 (8): 614. doi:10.1002/anie.197906141. 
  7. ↑ P. G. Jessop, in Handbook of Homogeneous Hydrogenation (Eds.: J. G. de Vries, C. J. Elsevier), Wiley-VCH, Weinheim, Germany, 2007, pp. 489–511.
  8. ↑ P. G. Jessop, F. Joó, C.-C. Tai, Recent advances in the homogeneous hydrogenation of carbon dioxide, Coord. Chem. Rev., 2004, 248, 2425–2442.doi:10.1016/j.ccr.2004.05.019
  9. ↑ Cohen, Julius B.: Practical Organic Chemistry MacMillan 1930
  10. ↑ L. F. Fieser and J. E. Jones (1955), Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv3p0590 ; Coll. Vol. 3: 590 
  11. ↑ ANTEATERS at the Natural History Collection of the University of Edinburgh
  12. ↑ US Code of Federal Regulations: 21 CFR 186.1316, 21 CFR 172.515
  13. ↑ "Methanol and Blindness". Ask A Scientist, Chemistry Archive. http://www.newton.dep.anl.gov/askasci/chem03/chem03561.htm. Retrieved 22 May 2007. 
  14. ↑ Makar AB, McMartin KE, Palese M, Tephly TR (1975). "Formate assay in body fluids: application in methanol poisoning". Biochem Med 13 (2): 117–26. doi:10.1016/0006-2944(75)90147-7. PMID 1. 

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