Formaldehyde
Encyclopedia : F : FO : FOR : Formaldehyde
| Formaldehyde | |
|---|---|
| |
| General | |
| Systematic name | methanal |
| Other names | formalin, formol, methyl aldehyde, methylene oxide |
| Molecular formula | CH2O |
| SMILES | C=O |
| Molar mass | 30.03 g/mol |
| Appearance | colourless gas |
| CAS number | [50-00-0] |
| Properties | |
| Density and phase | 1 kg/m3, gas |
| Solubility in water | > 100 g/100 ml (20 °C) |
| in ethanol, acetone, DMSO | > 100 g/100 ml |
| in ether, benzene, organic solvents | soluble |
| in chloroform | immiscible |
| Melting point | -117 °C (156 K) |
| Boiling point | -19.3 °C (253.9 K) |
| Vapor pressure | 3890 mm Hg at 25 °C |
| Structure | |
| Molecular shape | trigonal planar |
| Dipole moment | 2.33168(1) D |
| Hazards | |
| MSDS | External MSDS |
| Main hazards | toxic, flammable |
| NFPA 704 |   
|
| Flash point | -53 °C |
| R/S statement | R23/24/25, R34, R40, R43 S1/2, S26, S36/37, S39, S45, S51 |
| RTECS number | LP8925000 |
| Supplementary data page | |
| Structure and properties | n, εr, etc. |
| Thermodynamic data | Phase behaviour Solid, liquid, gas |
| Spectral data | UV, IR, NMR, MS |
| Related compounds | |
| Related aldehydes | acetaldehyde benzaldehyde |
| Related compounds | ketones carboxylic acids |
| Except where noted otherwise, data are given for materials in their standard state (at 25°C, 100 kPa) [Chemical infoboxInfobox disclaimer and references] | |
Formaldehyde readily results from the incomplete combustion of carbon-containing materials. It may be found in the smoke from forest fires, in automobile exhaust, and in tobacco smoke. In the atmosphere, formaldehyde is produced by the action of sunlight and oxygen on atmospheric methane and other hydrocarbons. Small amounts of formaldehyde are produced as a metabolic byproduct in most organisms, including humans.
Properties
Although formaldehyde is a gas at room temperature, it is readily soluble in water, and it is most commonly sold as a 37% solution in water called by trade names such as formalin or formol. In water, formaldehyde polymerizes, and formalin actually contains very little formaldehyde in the form of H2CO monomer. Usually, these solutions contain a few percent methanol to limit the extent of polymerization.Formaldehyde exhibits most of the general chemical properties of the aldehydes, except that is generally more reactive than other aldehydes. Formaldehyde is a potent electrophile. It can participate in electrophilic aromatic substitution reactions with aromatic compounds and can undergo electrophilic addition reactions with alkenes. In the presence of basic catalysts, formaldehyde undergoes a Cannizaro reaction to produce formic acid and methanol.
Formaldehyde reversibly polymerizes to produce its cyclic trimer, 1,3,5-trioxane or the linear polymer polyoxymethylene. Formation of these substances makes formaldehyde's gas behavior differ substantially from the ideal gas law, especially at high pressure or low temperature.
Formaldehyde is readily oxidized by atmospheric oxygen to form formic acid. Formaldehyde solutions must be kept tightly sealed to prevent this from happening in storage.
Production
Industrially, formaldehyde is produced by the catalytic oxidation of methanol. The most commonly used catalysts are silver metal or a mixture of an iron oxide with molybdenum and vanadium. In the more commonly used iron oxide system (Formox process), methanol and oxygen react at 250°C to produce formaldehyde according to the chemical equationThe silver-based catalyst is usually operated at a higher temperature, about 650 °C. On it, two chemical reactions simultaneously produce formaldehyde: the one shown above, and the dehydrogenation reaction
Further oxidation of the formaldehyde product during its production usually gives formic acid that is found in formaldehyde solution, found in ppm values.
On a smaller scale, formalin can be produced using a whole range of other methods including conversion from ethanol instead of the normally-fed methanol feedstock. Such methods however are of less commercial importance.
Uses
Formaldehyde kills most bacteria, and so a solution of formaldehyde in water is commonly used as a disinfectant. When he arrives at his room in the tuberculosis sanatorium in Thomas Mann's The Magic Mountain, Hans Castorp is told: "An American woman died here day before yesterday. . . . After they took her away of course they fumigated the room thoroughly with formalin, which is the proper thing to use in such cases" .It is also used to preserve biological specimens, and as a preservative in vaccinations. In medicine, formaldehyde solutions are applied topically to dry the skin, such as in the treatment of warts. Formaldehyde based solutions are used in embalming to disinfect and temporarily preserve human remains pending final disposition.
Most formaldehyde, however, is used in the production of polymers and other chemicals. When combined with phenol, urea, or melamine, formaldehyde produces a hard thermoset resin. These resins are commonly used in permanent adhesives, such as those used in plywood or carpeting; and as the wet-strength resin added to sanitary paper products such as (listed in increasing concentrations injected into the paper machine headstock chest) facial tissue, table napkins, and roll towels. They are also foamed to make insulation, or cast into molded products. Production of formaldehyde resins accounts for more than half of formaldehyde consumption.
Formaldehyde is still used in low concentrations for process C-41 (color negative film) stabilizer in the final wash step, as well as in the process E-6 pre-bleach step, to obviate the need for it in the final wash.
Formaldehyde is also used to make numerous other chemicals, used even in personal care products such as toothpaste. Many of these are polyfunctional alcohols such as pentaerythritol, which is used to make paints and explosives. Other formaldehyde derivatives include methylene diphenyl diisocyanate, an important component in polyurethane paints and foams, and hexamine, which is used in phenol-formaldehyde resins and to make the explosive RDX.
Formaldehyde cross links amino groups.
Formaldehyde, along with 18M (concentrated) sulfuric acid(the entire solution often called the Marquis reagent)http://www.dancesafe.org/documents/druginfo/testkits.php is used as an MDMA "testing kit" by such groups as Dancesafe as well as MDMA consumers.http://www.dancesafe.org/documents/druginfo/testkits.php The solution alone cannot verify the presence of MDMA, but reacts with many other chemicals that the ecstasy tablet itself may be cut with. The reaction itself produces colors which corrolate with such chemicals.
Health effects
Because formaldehyde resins are used in many construction materials, including plywood, carpet, and spray-on insulating foams, and because these resins slowly give off formaldehyde over time, formaldehyde is one of the more common indoor air pollutants. At concentrations above 0.1 mg/kg in air, inhaled formaldehyde can irritate the eyes and mucous membranes, resulting in watery eyes, headache, a burning sensation in the throat, and difficulty breathing.Large formaldehyde exposures, for example from drinking formaldehyde solutions, are potentially lethal. Formaldehyde is converted to formic acid in the body, leading to a rise in blood acidity, rapid, shallow breathing, hypothermia, and coma or death. People who have ingested formaldehyde require immediate medical attention.
In the body, formaldehyde can cause proteins to irreversibly bind to DNA. Laboratory animals exposed to large doses of inhaled formaldehyde over their lifetimes have developed more cancers of the nose and throat than are usual, as have workers in particle-board sawmills. However, some studies suggest that smaller concentrations of formaldehyde like those encountered in most buildings have no carcinogenic effects. Formaldehyde is classifed as a probable human carcinogen by the U.S. Environmental Protection Agency and as a known human carcinogen by the International Agency for Research on Cancer.
External links
- [International Chemical Safety Card 0275] --> (gas)
- [International Chemical Safety Card 0695] --> (solution)
- ["Formaldehyde"], IARC Monograph
- [Formaldehyde (gas)] from the 11th Report on Carcinogens of the U.S. National Toxicology Program (.pdf file)
- [Formaldehyde fact sheet] from the Australian National Pollutant Inventory
- [NIOSH Pocket Guide to Chemical Hazards]
- [Process C-41 Using KODAK FLEXICOLOR Chemicals Publication Z-131]
- For a full list of external links to MSDSs, spectroscopic data, commercial chemicals suppliers etc. for this compound, see [Chemical sources].
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