Formaldehyde

Formaldehyde is the paraformaldehyde. In water, it exists as the hydrate H₂C(OH)₂.

Formaldehyde is an intermediate in the oxidation (or combustion) of methane as well as other carbon compounds, e.g., forest fires, in automobile exhaust, and in tobacco smoke. In metabolic byproduct in most organisms, including humans.

Properties

Although formaldehyde is a ideal gas law, especially at high pressure or low temperature.

Production

In industry, formaldehyde is produced by the catalytic oxidation of chemical equation

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

Formaldehyde is readily formic acid. Formic acid is found in ppm levels in commercial formaldehyde.

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.

Organic chemistry

Formaldehyde is a central building-block in the synthesis of many other compounds. It exhibits most of the chemical properties of other aldehydes but is more reactive. Formaldehyde is a good formic acid and methanol.

Condensation with acetaldehyde affords pentaerythritol.^[2] Condensation with phenols gives phenol-formaldehyde resins. WIth 4-substituted phenols, one obtains calixarenes.^[3]

With hydrogen sulfide, it forms trithiane.^[4]

3 CH₂O + 3 H₂S → (CH₂S)₃ + 3 H₂O

Biology

Formaldehyde (and its Methanogenesis, which can start from many C1 sources, proceeds via the equivalent of formaldehyde, but this one-carbon species is masked as a methylene group carried by methanopterin.

As a disinfectant and biocide

An aqueous solution of formaldehyde can be useful as a disinfectant, as it kills most bacteria and fungi (including their spores). It is also used as a preservative in vaccinations. In medicine, formaldehyde solutions are applied topically to dry the skin, such as in the treatment of warts. Many aquarists use formaldehyde as a treatment for the parasite ichthyophthirius.

Formaldehyde preserves or fixes tissue or cells by irreversibly cross-linking primary amino groups in proteins with other nearby nitrogen atoms in protein or DNA through a -CH₂- linkage.

Formaldehyde is also used as a detergent in electrophoresis, preventing RNA from forming secondary structures.

Formaldehyde is converted to acidosis).

Industry

Formaldehyde is a common building block for the synthesis of more complex compounds and materials.

Most formaldehyde is used in the production of polymers and other chemicals. When combined with cast into moulded products. Production of formaldehyde resins accounts for more than half of formaldehyde consumption.

Many of these are polyfunctional alcohols such as pentaerythritol, which is used to make RDX.

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 used to produce glues used in the manufacture of particleboard, plywood, veneers, and other wood products, as well as spray-on insulating foams.^{[citation needed]}

Formaldehyde, along with 18 MDMA "testing kit" by such groups as Dancesafe as well as MDMA consumers. The solution alone cannot verify the presence of MDMA, but reacts with many other chemicals that the MDMA tablet itself may be adulterated with. The reaction itself produces colors that correlate with these components.

The textile industry uses formaldehyde-based resins as finishers to make fabrics crease-resistant.^{[citation needed]}

Embalming

Formaldehyde-based solutions are used in embalming to disinfect and temporarily preserve human remains. It is the ability of formaldehyde to fix the tissue that produces the tell-tale firmness of flesh in an embalmed body. Whereas other heavier aldehydes also produce a similar firming action, none approaches the completeness of formaldehyde. Several European countries restrict the use of formaldehyde, including the import of formaldehyde-treated products and embalming, and the European Union is considering a complete ban on formaldehyde usage (including embalming), subject to a review of List 4B of the Technical Annex to the Report from the Commission to the European Parliament and the Council on the Evaluation of the Active Substances of Plant Protection Products by the European Commission Services. Countries with a strong tradition of embalming corpses, such as Ireland and other colder-weather countries, have raised concerns. The European Union has decided on the date September 22, 2007 to ban Formaldehyde use throughout Europe, because of its carcinogenic properties.^[6]

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.^[7] Because formaldehyde resins are used in many construction materials, formaldehyde is one of the more common indoor air pollutants.^{[citation needed]} At concentrations above 0.1 ppm in air, formaldehyde can irritate the eyes and mucous membranes, resulting in watery eyes. If inhaled, formaldehyde at this concentration may cause headaches, a burning sensation in the throat, and difficulty breathing, as well as triggering or aggravating asthma symptoms.^[8] Formaldehyde is classified as a probable human carcinogen by the U.S. Environmental Protection Agency, which provides sufficient evidence that formaldehyde causes nasopharyngeal cancer in humans by the International Agency for Research on Cancer.^[9] 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^[10] Formaldehyde can cause allergies, and is part of the standard patch test series. People with formaldehyde allergy are advised to avoid formaldehyde-releasing chemicals as well (e.g. diazolidinyl urea).^[11]

References

1. ^ J Read, Text-Book of Organic Chemistry, G Bell & Sons, London, 1935
2. ^ H. B. J. Schurink (1941). "Pentaerythritol". Organic Syntheses, Collected Volume 1: 425.http://www.orgsyn.org/orgsyn/pdfs/CV1P0425.pdf
3. ^ Gutsche, C. D.; Iqbal, M. "p-tert-Butylcalix[4]arene" Organic Syntheses, Collected Volume 8, p.75 (1993); Vol. 68, p.234 (1990). http://www.orgsyn.org/orgsyn/pdfs/CV8P0075.pdf
4. ^ Bost, R. W.; Constable, E. W. "sym-Trithiane" Organic Syntheses, Collected Volume 2, p.610 (1943). http://www.orgsyn.org/orgsyn/pdfs/CV2P0610.pdf
5. ^ http://www.dancesafe.org/documents/druginfo/testkits.php
6. ^ http://www.webwire.com/ViewPressRel.asp?aId=41468
7. ^ IARC Press Release June 2004, http://www.iarc.fr/ENG/Press_Releases/archives/pr153a.html
8. ^ Symptoms of Low-Level Formaldehyde Exposures, Health Canada, http://www.hc-sc.gc.ca/iyh-vsv/environ/formaldehyde_e.html
9. ^ http://monographs.iarc.fr/ENG/Monographs/vol88/volume88.pdf "Formaldehyde".
10. ^ Testing for Indoor Air Quality, Baseline IAQ, and Materials, http://www.epa.gov/rtp/new-bldg/environmental/s_01445.htm
11. ^ Allergy to formaldehyde at DermNetNZ, http://dermnetnz.org/dermatitis/formaldehyde-allergy.html