Formaldehyde

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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	4 3 0
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, ε_r, 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) Infobox disclaimer and references

The chemical compound formaldehyde (also known as methanal) is a gas with a pungent smell. It is the simplest aldehyde. Its chemical formula is H₂CO. Formaldehyde was first synthesized by the Russian chemist Aleksandr Butlerov in 1859 but was conclusively identified by August Wilhelm von Hofmann in 1867.^{[citation needed]}

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.

1 Properties
2 Production
3 Uses
4 Health effects
5 External links

[edit] Properties

Although formaldehyde is a gas at room temperature, it is readily soluble in water. It is most commonly sold as a 37% aqueous solution with trade names such as formalin or formol. In water formaldehyde converts to the hydrate CH₂(OH)₂. Thus formalin contains very little H₂CO. These solutions usually contain a few percent methanol to limit the extent of polymerization.

Formaldehyde exhibits most of the chemical properties of the aldehydes, except that is more reactive. Formaldehyde is a good 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. Because of the formation of these derivatives, formaldehyde gas deviates strongly from the ideal gas law, especially at high pressure or low temperature.

Formaldehyde is also used as a detergent in RNA gel electrophoresis, inabeling RNA to form secondary structures.

Formaldehyde is readily oxidized by atmospheric oxygen to form formic acid. Formaldehyde solutions should be protected from air.

[edit] 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 equation

2 CH₃OH + O₂ → 2 H₂CO + 2 H₂O

The 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

CH₃OH → H₂CO + H₂

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 are of less commercial importance.

[edit] Uses

Formaldehyde kills most bacteria, and a solution of formaldehyde in water is commonly used as a disinfectant. Upon arrival 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" {1924; trans. H. T. Lowe-Porter,1927}.

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. Formaldehyde preserves or "fixes" tissue or cells by irreversibly connecting a primary amine group in protein with a nearby nitrogen in protein or DNA through a -CH2- linkage.

Most formaldehyde 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. It is used 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 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. It is this action that produces the tell-tale firmness of flesh in an embalmed body. While other, heavier aldehydes also produce a similar firming action, none approaches the completeness of formaldehyde.

Formaldehyde, along with 18M (concentrated) sulfuric acid (the entire solution often called the Marquis reagent)^[1] is used as an MDMA "testing kit" by such groups as Dancesafe as well as MDMA consumers.^[2] 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 correlate with such chemicals.

[edit] 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 (acidosis), rapid, shallow breathing, blurred vision or complete blindness, hypothermia, and, in the most severe cases, 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.