Formaldehyde ( methanal)
IUPAC name	Methanal
Other names	formol, methyl aldehyde, methylene oxide
Identifiers
CAS number	50-00-0
RTECS number	LP8925000
SMILES	C=O
ChemSpider ID	692
Properties
Molecular formula	CH2O
Molar mass	30.03 g·mol−1
Appearance	colorless gas
Density	1 kg·m−3, gas
Melting point	-117 °C (156 K)
Boiling point	-19.3 °C (253.9 K)
Solubility in water	> 100 g/100 ml (20 °C)
Structure
Molecular shape	trigonal planar
Dipole moment	2.33168(1) D
Hazards
Main hazards	Toxic, Flammable, Carcinogenic
NFPA 704	2 3 2
R-phrases	R23/24/25, R34, R40, R43
S-phrases	(S1/2), S26, S36/37, S39, S45, S51
Flash point	-53 °C
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 references

Formaldehyde (IUPAC name methanal) is a chemical compound with the formula H₂CO. It is the simplest aldehyde. Formaldehyde exists in several forms aside from H₂CO: the cyclic trimer trioxane and the polymer paraformaldehyde. It exists in water as the hydrate H₂C(OH)₂. Aqueous solutions of formaldehyde are referred to as formalin. "100%" formalin consists of a saturated solution of formaldehyde (roughly 40% by mass) in water, with a small amount of stabilizer, usually methanol to limit oxidation and polymerization. It is produced on a substantial scale of 6M tons/y. In view of its widespread use, toxicity, and volatility, exposure to formaldehyde is significant consideration for human health.^[1]

[edit] Occurrence

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. When produced in the atmosphere by the action of sunlight and oxygen on atmospheric methane and other hydrocarbons, it becomes part of smog.

[edit] Biological occurrence

Formaldehyde (and its oligomers and hydrates) are rarely encountered in living organisms. Methanogenesis proceeds via the equivalent of formaldehyde, but this one-carbon species is masked as a methylene group in methanopterin. Formaldehyde is the primary cause of methanol's toxicity, since methanol is metabolised into toxic formaldehyde by alcohol dehydrogenase. Formaldehyde is converted to formic acid in the body.

[edit] Interstellar formaldehyde

[edit] Initial Discovery

Formaldehyde was first discovered in interstellar space in 1969 by L. Snyder et al.. using the National Radio Astronomy Observatory. H₂CO was detected by means of the 1₁₁ - 1₁₀ ground state rotational transition at 4830 MHz ^[2].

[edit] Subsequent detections

Formaldehyde was the first polyatomic organic molecule detected in the interstellar medium^[3] and since its initial detection has been observed in many regions of the galaxy. The isotopic ratio of [¹²C]/[¹³C] was determined to be about or less than 50% in the galactic disk ^[4]. Formaldehyde has been used to map out kinematic features of dense clouds located near Gould's Belt of local bright stars ^[5]. In 2007, the first H₂CO 6 cm maser flare was detected^[6]. It was a short duration outburst in IRAS 18566 + 0408 that produced a line profile consistent with the superposition of two Gaussian components, which leads to the belief that an event outside the maser gas triggered simultaneous flares at two different locations^[6]. Although this was the first maser flare detected, H₂CO masers have been observed since 1974 by Downes and Wilson in NGC 7538^[7]. According to Araya et al.., H₂CO are different from other masers in that they are weaker than most other masers (such as OH, CH₃OH, and H₂O) and have only been detected near very young massive stellar objects ^[8]. Unlike OH, H₂O, and CH₃OH, only five galactic star forming regions have associated formaldehyde maser emission, which has only been observed through the 1₁₀ → 1₁₁ transition^[7]. Because of the widespread interest in interstellar formaldehyde it has recently been extensively studied, yielding new extragalactic sources, including NGC 253, NGC 520, NGC 660, NGC 891, NGC 2903, NGC 3079, NGC 3628, NGC 6240, NGC 6946, IC 342, IC 860, Arp 55, Arp 220, M82, M83, IRAS 10173+0828, IRAS 15107+0724, and IRAS 17468+1320^[9].

[edit] Interstellar reactions

The gas-phase reaction that produces formaldehyde possesses modest barriers and is too inefficient to produce the abundance of formaldehyde that has been observed^[10]. One proposed mechanism for the formation is the hydrogenation of CO ice, shown below^[10].

H + CO --> HCO + H --> H₂CO (rate constant=9.2*10^-3 s^-1)

This is the basic production mechanism leading to H₂CO; there are several side reactions that take place with each step of the reaction that are based on the nature of the ice on the grain according to David Woon^[10]. The rate constant presented is for the hydrogenation of CO. The rate constant for the hydrogenation of HCO was not provided as it was much larger than that of the hydrogenation of CO, likely due to the fact that HCO is a radical^[11]. Awad et al.. mention that this is a surface level reaction only and only the monolayer is considered in calculations; this includes the surface within cracks in the ice^[11].

Formaldehyde is relatively inactive in gas phase chemistry in the interstellar medium. Its action is predominantly focused in grain-surface chemistry on dust grains in interstellar clouds^[12],[13]. Reactions involving formaldehyde have been observed to produce molecules containing C-H, C-O, O-H, and C-N bonds^[13]. While these products are not necessarily well known, Schutte et al.. believe these to be typical products of formaldehyde reactions at higher temperatures, polyoxymethylene, methanolamine, methanediol, and methoxyethanol for example (see Table 2^[12]). Formaldehyde is believed to be the primary precursor for most of the complex organic material in the interstellar medium, including amino acids^[13]. Formaldehyde most often reacts with NH₃, H₂O, CH₃OH, CO, and itself, H₂CO^[12],[13]. The three dominating reactions are shown below^[12].

H₂CO + NH₃ --> amine (when [NH₃]:[H₂CO] > .2)

H₂CO + H₂O --> diols (always dominate as [H₂O] > [H₂CO])

H₂CO + H₂CO --> [-CH₂-O-]_n (catalyzed by NH₃ when [NH₃]:[H₂CO] > .005)

There is no kinetic data available for these reactions as the entire reaction is not verified nor well understood. These reactions are believed to take place during warm-up of the ice on grains which releases the molecules to react. These reactions begin at temperatures as low as 40K - 80K but may take place at even lower temperatures.

Note that many other reactions are listed on the UMIST RATE06 database.

[edit] Importance of observation

Formaldehyde appears to be a useful probe for astrochemists due to its low reactivity in the gas phase and to the fact that the 1₁₀ - 1₁₁ and 2₁₁ - 2₁₂ K-doublet transitions are rather clear. Formaldehyde has been used in many capacities and to investigate many systems including,

• Determination of the [¹²C]/[¹³C] ratio to be less than 50% in the galactic disc^[4].
• Mapping of the kinematic features of dark clouds located near Gould's Belt of local bright stars^[5]. The radial velocities determined for these clouds lead Sandqvist et al. to believe that the clouds participate in the expansion of the local system of H gas and bright stars^[5].
• Determination of the temperature of molecular formation from the ratio of ortho-/para- H₂CO. H₂CO is a good candidate for this process because of the near zero probability of nuclear spin conversion in gas phase protostar environments^[14].
• Determination of the spatial density of H₂ and dense gas mass in several galaxies with varying luminosity (see Subsequent Discoveries for list of galaxies)^[9]. The spatial densities calculated fell in the range of 10^4.7 to 10^5.7 cm^-3 and dense gas masses calculated fell in the range of 0.6x10⁸ to 0.77x10⁹ solar masses^[9]. Mangum _et al_. noticed that the galaxies with lower infrared luminosity had lower dense gas masses and that this seemed to be a real trend despite the small data set^[9].

[edit] Rotational spectrum

Above is the rotational spectrum at the ground state vibrational level of H₂CO at 30 K. This spectrum was simulated using Pgopher and S-Reduction Rotational constants from Muller et al.^[15]. The observed transitions are the 6.2 cm 1₁₁ - 1₁₀ and 2.1 cm 2₁₂ - 2₁₁ K-doublet transitions. At right is the rotational energy level diagram. The ortho/para splitting is determined by the parity of K_a, ortho if K_a is odd and para if K_a is even^[14].

[edit] Synthesis and industrial production

Formaldehyde was first reported by the Russian chemist Aleksandr Butlerov (1828-1886), but was conclusively identified by August Wilhelm von Hofmann.^[16]

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:^[1]

2 CH₃OH + O₂ → 2 H₂CO + 2 H₂O

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.^[1]

[edit] Organic chemistry

Formaldehyde is a building block in the synthesis of many other compounds of specialized and industrial significance. It exhibits most of the chemical properties of other aldehydes but is more reactive. For example it is more readily oxidized by atmospheric oxygen to formic acid (formic acid is found in ppm levels in commercial formaldehyde). Formaldehyde is a good electrophile, participating in electrophilic aromatic substitution reactions with aromatic compounds, and can undergo electrophilic addition reactions with alkenes and aromatics. Formaldehyde undergoes a Cannizzaro reaction in the presence of basic catalysts to produce formic acid and methanol.

[edit] Examples of organic synthetic applications

Condensation with acetaldehyde affords pentaerythritol, a chemical necessary in synthesizing PETN, a high explosive.^[17] Condensation with phenols gives phenol-formaldehyde resins. With 4-substituted phenols one obtains calixarenes.^[18]

When combined with hydrogen sulfide it forms trithiane.^[19]

3 CH₂O + 3 H₂S → (CH₂S)₃ + 3 H₂O

[edit] Industrial applications

Formaldehyde is a common building block for the synthesis of more complex compounds and materials. In approximate order of decreasing consumption, products generated from formaldehyde include urea formaldehyde resin, melamine resin, phenol formaldehyde resin, polyoxymethylene plastics, 1,4-butanediol, and methylene diphenyl diisocyanate.^[1]

When reacted with phenol, urea, or melamine formaldehyde produces, respectively, hard thermoset phenol formaldehyde resin, urea formaldehyde resin, and melamine resin, which 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 moulded products. Production of formaldehyde resins accounts for more than half of formaldehyde consumption.

Formaldehyde is also a precursor to 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 as well as the explosive RDX.

The textile industry uses formaldehyde-based resins as finishers to make fabrics crease-resistant.^[20]

It is also used as an ingredient by some shampoo manufacturers.^{[citation needed]}

[edit] Miscellaneous applications

Formaldehyde is a common component of many niche uses. Formaldehyde, along with 18 M (concentrated) sulfuric acid (the entire solution often called the Marquis reagent)^[21], is used as an 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.

[edit] 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 vaccines. Formaldehyde solutions are applied topically in medicine to dry the skin, such as in the treatment of warts. Many aquarists use formaldehyde as a treatment for the parasites ichthyophthirius and Cryptocaryon irritans.^[22]

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. This is exploited in ChIP-on-chip transcriptomics experiments. Formaldehyde is also used as a denaturing agent in RNA gel electrophoresis, preventing RNA from forming secondary structures.

[edit] In photography

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.

[edit] Tissue fixative and embalming agent

Formaldehyde solutions are used as a fixative for microscopy and histology. Formaldehyde-based solutions are also used in embalming to disinfect and temporarily preserve human and animal remains. It is the ability of formaldehyde to fix the tissue that produces the tell-tale firmness of flesh in an embalmed body. 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 decided on September 22, 2007 to ban Formaldehyde use throughout Europe due to its carcinogenic properties.^[23]

[edit] 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.^[24] Because formaldehyde resins are used in many construction materials it is one of the more common indoor air pollutants.^[25] At concentrations above 3 ppb 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.^[26][27]

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. ^[28] 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.^[29] On April 11th, 2008, FEMA announced that all trailers purchased by that agency in the future must meet the same standard.^[30]

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).^[31] Formaldehyde has been banned in cosmetics in both Sweden and Japan.^{[citation needed]}

[edit] FEMA trailer incidents

[edit] Hurricane Katrina & Rita

In the U.S. the Federal Emergency Management Agency (FEMA) provided travel trailers and mobile homes starting in 2006 for habitation by residents of the U.S. gulf coast displaced by Hurricane Katrina and Hurricane Rita. Some of the people who moved into the trailers complained of breathing difficulties, nosebleeds, and persistent headaches. Formaldehyde-catalyzed resins were used in the production of these homes.

The United States Centers For Disease Control and Prevention (CDC) performed indoor air quality testing for formaldehyde ^[32] in some of the units. On Thursday, February 14, 2008 the CDC announced that potentially hazardous levels of formaldehyde were found in many of the travel trailers and mobile homes provided by the agency.^[33][34] The CDC's preliminary evaluation of a scientifically established random sample of 519 travel trailers and mobile homes tested between Dec. 21, 2007 and Jan. 23, 2008 (2+ years after manufacture) showed average levels of formaldehyde in all units of about 77 parts per billion (ppb). Long-term exposure to levels in this range can be linked to an increased risk of cancer and, at levels above this range, there can also be a risk of respiratory illness. These levels are higher than expected in indoor air, where levels are commonly in the range of 10-20 ppb, and are higher than the Agency for Toxic Substance Disease Registry (ATSDR, division of the CDC) Minimal Risk Level (MRL) of 8 ppb ^[35]. Levels measured ranged from 3 ppb to 590 ppb.^[36]

The Federal Emergency Management Agency, which requested the testing by the CDC, said it would work aggressively to relocate all residents of the temporary housing as soon as possible. Lawsuits are being filed against FEMA as a result of the exposures.^[37]

[edit] Iowa Floods of 2008

Also in the U.S., problems arose in trailers again provided by FEMA to residents displaced by the Iowa floods of 2008. A couple months after moving to the trailers, occupants reported violent coughing, headaches, as well as Asthma, Bronchitis, and other problems. Tests showed that in some trailers levels of formaldehyde exceeded the limits recommended by the U.S. Environmental Protection Agency and American Lung Association.^[38].^[39] The associated publicity has resulted in additional testing to begin in November.^[40]

[edit] Contaminant in Food

Scandals have broken in both 2005 Indonesia food scare and 2007 Vietnam food scare regarding the addition of formaldehyde to foods to extend shelf life. Foods known to be contaminated include noodles, salted fish, tofu, and rumors of chicken and beer. In humans, it is known to cause a number of detrimental effects including cancer.

[edit] References

1. ^ ^{a b c d} G. Reuss, W. Disteldorf, A. O. Gamer, A. Hilt, “Formaldehyde” in Ullmann’s Encyclopedia of Industrial Chemistry Wiley-VCH, 2005, Weinheim.
2. ^ Snyder, L. E., Buhl, D., Zuckerman, B., & Palmer, P. 1969, Phys. Rev. Lett., 22, 679
3. ^ Zuckerman, B.; Buhl, D.; Palmer, P.; Snyder, L. E. 1970, Astrophysical Journal, 160, 485
4. ^ ^{a b} Henkel, C.; Guesten, R.; Gardner, F. F. 1985, Astronomy and Astrophysics, 143, 148
5. ^ ^{a b c} Sandqvist, A.; Tomboulides, H.; Lindblad, P. O. 1988, Astronomy and Astrophysics, 205, 225
6. ^ ^{a b} Araya, E. _et al_. 2007, Astrophysical Journal, 654, L95
7. ^ ^{a b} Hoffman, I. M.; Goss, W. M.; Palmer, P. 2007, Astrophysical Journal, 654, 971
8. ^ Araya et al. 2007, Astrophysical Journal, 669, 1050
9. ^ ^{a b c d} J. G. Mangum et al. 2008, Astrophysical Journal, 673, 832.
10. ^ ^{a b c} Woon, D.E. 2002, Astrophysical Journal, 569, 541.
11. ^ ^{a b} Awad et al. 2005, Astrophysical Journal, 626, 262.
12. ^ ^{a b c d} W. A. Schutte et al. 1993, Science, 259, 1143.
13. ^ ^{a b c d} W. A. Schutte et al. 1993, Icarus, 104, 118.
14. ^ ^{a b} M. Tudorie et al. 2006, Astronomy and Astrophysics, 453, 755.
15. ^ H. S. P. Muller et al. 2000, Journal of Molecular Spectroscopy, 200, 143.
16. ^ J Read, Text-Book of Organic Chemistry, G Bell & Sons, London, 1935
17. ^ H. B. J. Schurink (1941). "Pentaerythritol". Org. Synth. 1: 425; Coll. Vol. 1. 
18. ^ Gutsche, C. D.; Iqbal, M. (1993). "p-tert-Butylcalix[4]arene". Org. Synth.; Coll. Vol. 8: 75. 
19. ^ Bost, R. W.; Constable, E. W. (1943). "sym-Trithiane". Org. Synth.; Coll. Vol. 2: 610. 
20. ^ FORMALDEHYDE IN CLOTHING AND OTHER TEXTILES
21. ^ DanceSafe: testing kit info
22. ^ University of Florida - Use of Formalin to Control Fish Parasites http://edis.ifas.ufl.edu/VM061
23. ^ Formaldehyde Ban set for 22 Sept 2007
24. ^ IARC Press Release June 2004, http://www.iarc.fr/ENG/Press_Releases/archives/pr153a.html
25. ^ Indoor Air Pollution in California, Final Report, California Air Resources Board (2005) http://www.arb.ca.gov/research/indoor/ab1173/finalreport.htm, at pages 65 – 70.
26. ^ http://www.oehha.ca.gov/air/chronic_rels/AllChrels.html California Office Of Health Hazard Assessment
27. ^ Symptoms of Low-Level Formaldehyde Exposures, Health Canada, http://www.hc-sc.gc.ca/iyh-vsv/environ/formaldehyde_e.html
28. ^ http://monographs.iarc.fr/ENG/Monographs/vol88/volume88.pdf "Formaldehyde".
29. ^ Testing for Indoor Air Quality, Baseline IAQ, and Materials, http://www.epa.gov/rtp/new-bldg/environmental/s_01445.htm
30. ^ In the US, FEMA limits formaldehyde in trailers, Boston.com, referenced 9/4/2008[1]
31. ^ "Formaldehyde allergy: What is formaldehyde and where is it found?". DermNet NZ.
32. ^ http://www.cdc.gov/niosh/nmam/pdfs/2016.pdf
33. ^ Formaldehyde Levels in FEMA-Supplied Trailers
34. ^ Mike Brunker (2006-07-25). "Are FEMA trailers ‘toxic tin cans’?", MSNBC. 
35. ^ ATSDR - Minimal Risk Levels for Hazardous Substances (MRLs)
36. ^ FEMA: CDC Releases Results Of Formaldehyde Level Tests
37. ^ Suit Filed Over FEMA Trailer Toxins - washingtonpost.com
38. ^ Megan Terlecky (2008-10-24). "How We Tested for Formaldehyde", KGAN-TV. 
39. ^ NIGEL DUARA (2008-10-21). "FEMA disputes formaldehyde study of Iowa trailers", Associated Press. 
40. ^ Cindy Hadish (2008-10-24). "FEMA meets with mobile home residents over health concerns", Cedar Rapids Gazette. 

[edit] 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
• Formaldehyde Council
• Formaldehyde Data Sheet, ChemSub Online
• Prevention guide – Formaldehyde in the work place
• National Institute for Occupational Safety and Health - Formaldehyde Page