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Encyclopedia > Formalin


Name Formaldehyde

The center of this image represents a carbon atom.

Chemical formula H2CO
Formula weight 30.03 g/mol
Synonyms methanal, methyl aldehyde, methylene oxide
CAS number 50-00-0

Phase behavior

Melting point 156.2 K (−116.9 C)
Boiling point 254.1 K (-19.0 C)
Triple point 155.1 K (-118.0 C)
? Pa
Liquid density 1130 kg/m3

Liquid thermochemistry

ΔfH0gas -115.9 kJ/mol
S0gas 219.0 J/(molK)
Cp 35.4 J/molK


Acute effects Toxic. May cause irritation to mucous membranes, difficulty breathing, lowered body temperature, lethargy, coma, and death.
Chronic effects May cause cancer of the nose and mucous membranes.
Flash point -53 C
Autoignition temperature 430 C
Explosive limits 7–73%

More info

Properties NIST WebBook (http://webbook.nist.gov/cgi/cbook.cgi?ID=C50000&Units=SI)
MSDS Hazardous Chemical Database (http://ull.chemistry.uakron.edu/erd/chemicals1/7/6526.html)

SI units were used where possible. Unless otherwise stated, standard conditions were used.

Disclaimer and references

The chemical compound formaldehyde (also known by IUPAC nomenclature as methanal), is a gas with a strong pungent smell. It is the simplest aldehyde. Its chemical formula is HCHO, sometimes rendered as H2CO. It has a boiling point of -21C (262 K). Formaldehyde was discovered by the Russian chemist Aleksandr Butlerov in 1859.

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.



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 HCHO 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.


Industrially, formaldehyde is produced by the catalytic oxidation of methanol. The most commonly used catalysts are silver metal and a mixture of an iron oxide with molybdenum. In the more commonly used iron oxide system, methanol and oxygen react at 400C to produce formaldehyde according to the chemical equation

CH3OH + O2 → HCHO + H2O

The silver-based catalyst is usually operated at a higher temperature, about 650C. On it, two chemical reactions simultaneously produce formaldehyde: the one shown above, and the dehydrogenation reaction



Formaldehyde kills most bacteria, and so a solution of formaldehyde in water is commonly used as a disinfectant or to preserve biological specimens. It is also used as a preservative in vaccinations.

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. 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 also used to make numerous other chemicals. Many of these are polyfunctional alcohols such as pentaerythritol, which is used to make paints and explosives. Other formaldehyde derivatives include diphenylmethane diisocyanate, an important component in polyurethane paints and foams, and hexamethylene tetramine, which is used in phenol-formaldehyde resins and to make the explosive RDX.

Formaldehyde cross links amino groups.

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.

  Results from FactBites:
Use of Formalin to Control Fish Parasites (1644 words)
Formalin is a generic term which describes a solution of 37% formaldehyde gas dissolved in water.
Formalin is a liquid formulation of 37% formaldehyde gas dissolved in water.
Formalin is an excellent parasiticide for use in tanks and aquaria, but its use in ponds is discouraged because it chemically removes oxygen from the water and can contribute to catastrophic oxygen depletion under pond conditions.
Formalin (1008 words)
It is very important to note that the formalin compound readily available as a treatment for fish is the EXACT and same compound used in embalming practices.
But before you go thinking formalin is an ideal anti-bacterial treatment, first consider how formaldehyde “kills.” Unlike most anti-bacterial and germicidal agents which poison the bacteria and germ cells, formaldehyde kills cell tissue by dehydrating the tissue and bacteria cells and replacing the normal fluid in the cells with a gel-like rigid compound.
This is an important point to consider when using formalin on fish as the fish will “absorb” a certain level of formalin into its tissue and cell structures just by the very nature of how fish process water in their environment.
  More results at FactBites »



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