Formaldehyde

Introduction

The chemical compound formaldehyde (also known by its IUPAC name 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 -21 °C (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 cigarette 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.

Formaldehyde is an important chemical used widely by industry to manufacture building materials and numerous household products. It is also a by-product of combustion and certain other natural processes. Thus, it may be present in substantial concentrations both indoors and outdoors.

Sources of formaldehyde in the home include building materials, smoking, household products, and the use of un-vented, fuel-burning appliances, like gas stoves or kerosene space heaters. Formaldehyde, by itself or in combination with other chemicals, serves a number of purposes in manufactured products. For example, it is used to add permanent-press qualities to clothing and draperies, as a component of glues and adhesives, and as a preservative in some paints and coating products.

In homes, the most significant sources of formaldehyde are likely to be pressed wood products made using adhesives that contain urea-formaldehyde (UF) resins. Pressed wood products made for indoor use include: particleboard (used as sub-flooring and shelving and in cabinetry and furniture); hardwood plywood paneling (used for decorative wall covering and used in cabinets and furniture); and medium density fiberboard (used for drawer fronts, cabinets, and furniture tops). Medium density fiberboard contains a higher resin-to-wood ratio than any other UF pressed wood product and is generally recognized as being the highest formaldehyde-emitting pressed wood product.

Other pressed wood products, such as softwood plywood and flake or oriented strand board, are produced for exterior construction use and contain the dark, or red/black-colored phenol-formaldehyde (PF) resin. Although formaldehyde is present in both types of resins, pressed woods that contain PF resin generally emit formaldehyde at considerably lower rates than those containing UF resin.

Structure

Alternative names for formaldehyde

Formaldehyde is also known by several other names. These include:

• Formalin
• Methanal
• Methyl aldehyde
• Methylene oxide
• Morbicid acid
• Oxymethylene

Further information

Formula: CH₂0
CAS number: 50-00-0
Cross reactions: possibly glutaraldehyde
Appearance: clear, colourless liquid
Sensitiser: free formaldehyde, formaldehyde resins
Patch Test:
2% aqueous solution of formalin (40% solution of formaldehyde gas)
10% urea formaldehyde in petrolatum
10% melamine formaldehyde in petrolatum
1% other formaldehyde resins in petrolatum or isopropyl alcohol

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 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, and it can participate is electrophilic aromatic substitution reactions with aromatic compounds, and it can undergo electrophilic addition reactions with alkenes. In the presence of basic catalysts, formaldehyde undergoes a Cannizaro reaction to prouduce 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

Formaldehyde was first reported by the Russian chemist Aleksandr Butlerov (1828-1886), but was conclusively identified by August Wilhelm von Hofmann.

Formaldehyde is produced industrially by the catalytic oxidation of methanol. The most common catalysts are silver metal or a mixture of an iron and molybdenum or vanadium oxides. In the more commonly used FORMOX process methanol and oxygen react at ca 250-400 °C in presence of iron oxide in combination with molybdenum and/or vanadium to produce formaldehyde according to the chemical equation:

2CH₃OH + O₂ -> 2H₂CO + 2H₂O

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

CH₃OH -> H₂CO + H₂

Formalin can be produced on a smaller scale 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.

In principle formaldehyde could be generated by oxidation of methane, but this route is not industrially viable because the formaldehyde is more easily oxidized than methane.

Uses

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.

Sources of Formaldehyde

Pressed wood products (hardwood plywood wall paneling, particleboard, fiberboard) and furniture made with these pressed wood products. Urea-formaldehyde foam insulation (UFFI). Combustion sources and environmental tobacco smoke. Durable press drapes, other textiles, and glues.

Health Effects

Formaldehyde, a colorless, pungent-smelling gas, can cause watery eyes, burning sensations in the eyes and throat, nausea, and difficulty in breathing in some humans exposed at elevated levels (above 0.1 parts per million). High concentrations may trigger attacks in people with asthma. There is evidence that some people can develop a sensitivity to formaldehyde. It has also been shown to cause cancer in animals and may cause cancer in humans.  Health effects include eye, nose, and throat irritation; wheezing and coughing; fatigue; skin rash; severe allergic reactions. May cause cancer. May also cause other effects listed under "organic gases."  EPA's Integrated Risk Information System profile -

Levels in Homes

Average concentrations in older homes without UFFI are generally well below 0.1 (ppm). In homes with significant amounts of new pressed wood products, levels can be greater than 0.3 ppm.

Steps to Reduce Exposure

• Use "exterior-grade" pressed wood products (lower-emitting because they contain phenol resins, not urea resins).
• Use air conditioning and dehumidifiers to maintain moderate temperature and reduce humidity levels.
• Increase ventilation, particularly after bringing new sources of formaldehyde into the home.

Ask about the formaldehyde content of pressed wood products, including building materials, cabinetry, and furniture before you purchase them.

If you experience adverse reactions to formaldehyde, you may want to avoid the use of pressed wood products and other formaldehyde-emitting goods. Even if you do not experience such reactions, you may wish to reduce your exposure as much as possible by purchasing exterior-grade products, which emit less formaldehyde.

Some studies suggest that coating pressed wood products with polyurethane may reduce formaldehyde emissions for some period of time. To be effective, any such coating must cover all surfaces and edges and remain intact. Increase the ventilation and carefully follow the manufacturer instructions while applying these coatings. (If you are sensitive to formaldehyde, check the label contents before purchasing coating products to avoid buying products that contain formaldehyde, as they will emit the chemical for a short time after application.)

Maintain moderate temperature and humidity levels and provide adequate ventilation.

The rate at which formaldehyde is released is accelerated by heat and may also depend somewhat on the humidity level. Therefore, the use of dehumidifiers and air conditioning to control humidity and to maintain a moderate temperature can help reduce formaldehyde emissions. (Drain and clean dehumidifier collection trays frequently so that they do not become a breeding ground for microorganisms.) Increasing the rate of ventilation in your home will also help in reducing formaldehyde levels.

organic synthetic applications

Condensation with acetaldehyde affords pentaerythritol. Â Condensation with phenols gives phenol-formaldehyde resins. With 4-substituted phenols one obtains calixarenes.

When combined with hydrogen sulfide it forms trithiane.

3CH₂O + 3H₂S -> (CH₂S)₃ + 3H₂O

Health Effect

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 ppm in air, inhaled formaldehyde can irritate the eyes and mucus 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 mills. However, some studies suggest that smaller concentrations of formaldehyde like those encountered in most buildings have no carcinogenic effects. Formaldehyde is listed as a probable human carcinogen.

Safety

Occupational exposure to formaldehyde by inhalation is mainly from three types of sources: thermal or chemical decomposition of formaldehyde-based resins, formaldehyde emission from aqueous solutions (for example, embalming fluids), and the production of formaldehyde resulting from the combustion of a variety of organic compounds (for example, exhaust gases). Formaldehyde can be toxic, allergenic, and carcinogenic. Because formaldehyde resins are used in many construction materials it is one of the more common indoor air pollutants. At concentrations above 0.1 ppm in air formaldehyde can irritate the eyes and mucous membranes, resulting in watery eyes. Formaldehyde inhaled at this concentration may cause headaches, a burning sensation in the throat, and difficulty breathing, as well as triggering or aggravating asthma symptoms.

Formaldehyde is classified as a probable human carcinogen by the U.S. Environmental Protection Agency. The International Agency for Research on Cancer (IARC) has determined that there is "sufficient evidence" that occupational exposure to formaldehyde causes nasopharyngeal cancer in humans. The United States Environmental Protection Agency USEPA allows no more than 0.016 ppm formaldehyde in the air in new buildings constructed for that agency. On April 11th, 2008, FEMA announced that all trailers purchased by that agency in the future must meet the same standard.

Formaldehyde can cause allergies and is part of the standard patch test series. People with formaldehyde allergy are advised to avoid formaldehyde releasers as well (e.g., Quaternium-15, imidazolidinyl urea, and diazolidinyl urea). Formaldehyde has been banned in cosmetics in both Sweden and Japan.

Formaldehyde allergy

What are the reactions to formaldehyde allergy?

Reactions to formaldehyde depend on the type of exposure that has occurred. Formaldehyde is not only a sensitizer but also a potent primary irritant. Exposure to formaldehyde gas may cause burning sensations in the eye, nose and throat, skin rashes, tightness of the chest and wheezing, fatigue and headaches. These symptoms may be a result of a primary irritant effect or an allergic sensitization to formaldehyde.

Frequent or prolonged exposure may cause hypersensitivity, leading to the development of allergic contact dermatitis. This may occur through skin contact with formaldehyde containing products or with clothing made from fabrics containing formaldehyde. Dermatitis caused by clothing tends to affect parts of the body where there is greatest friction between the skin and fabric, for example "trouser dermatitis" is usually apparent on the inner thighs, gluteal folds and backs of the knees. Sweating may also be a factor in causing the allergic dermatitis as sweat or sebum appears to leach free formaldehyde from formaldehyde resins. Individuals sensitive to formaldehyde are not necessarily hypersensitive to formaldehyde resins. Clothing dermatitis appears to affect women more than men.
In individuals who are highly sensitive, contact with minute amounts of formaldehyde or being in a room where a bottle of formaldehyde may have been open previously thus leaving residual gas, can cause dermatitis.

What should I do to avoid formaldehyde ellergy?

It is difficult to avoid all exposure to formaldehyde because it is normally present at low levels (usually <0.03 ppm) in both indoor and outdoor air. For most people low-level exposure (up to 0.1 ppm) does not cause any problems. Methods to avoid or minimize exposure are described in the table below.

Methods to avoid or minimize exposure to high levels of formaldehyde

• Wear clothing made of 100% cotton, polyester, nylon or acrylic; these fabrics generally contain less formaldehyde and are usually well tolerated by sensitive individuals
• Avoid all clothing made with fabrics that have been treated with formaldehyde (see above)
• In general, machine wash all new clothing and bedding in hot, soapy water several times before use
• Purchase furniture made of pressed wood products only if the surfaces and edges are laminated or coated
• Occupational exposure can be reduced by identifying potential sources of exposure (material safety data sheets should be available to employees) and taking precautions to minimize exposure by wearing suitable protective garments
• To reduce the formaldehyde content in the air, increase ventilation by opening doors and windows and/or installing exhaust fans in closed areas
• Read product labels and avoid not only formaldehyde itself but also formaldehyde-releasing preservatives. Some of these are known by the following names:
• Quaternium-15
• 2-bromo-2nitropropane-1,3-diol
• imidazolidinyl urea
• diazolidinyl urea

References:

www.epa.gov/iris/subst/0419.htm
en.wikipedia.org
www.3dchem.com
wwww.knowledgerush.com
www.daviddarling.info
www.3dchem.com
www.experiencefestival.com
www.reference.com
www.questia.com

Editorial Team, Mindfiesta