Paraformaldehyde
| Paraformaldehyde | |
|---|---|
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Polyoxymethylene |
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| Identifiers | |
| CAS number | 30525-89-4  |
| PubChem | 24898648 |
| Properties | |
| Molecular formula | OH(CH2O)nH (n = 8 - 100) |
| Appearance | white crystalline solid |
| Density | 0.88 g·cm−3 (20 °C) |
| Melting point |
120 °C |
| Solubility in water | low |
| Hazards | |
| MSDS | Oxford MSDS |
| EU classification | Toxic (T); Corrosive (C) |
 (verify) (what is:  / ?)Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
Paraformaldehyde (PFA) is the smallest polyoxymethylene, it is the condensation reaction product of formaldehyde with a typical degree of polymerization of 8–100 units. Paraformaldehyde commonly has a slight odor of formaldehyde due to decomposition. Paraformaldehyde is a poly-acetal.
Contents |
[edit] Synthesis
Paraformaldehyde forms slowly in aqueous formaldehyde solutions (formalin) as a white precipitate, especially if stored in the cold. Formalin actually contains very little monomeric formaldehyde; most of it forms short chains of polyformaldehyde. A few percent of methanol is often added as a stabilizer to limit the extent of polymerization.
[edit] Reactions
Paraformaldehyde can be depolymerized to formaldehyde gas by dry heating[1] and to formaldehyde solution by water in the presence of an acid or heat. The very pure formaldehyde solutions obtained in this way are used as a fixative for microscopy and histology.
Paraformaldehyde is flammable as it decomposes in the heat into the flammable gas formaldehyde.
[edit] Uses
Paraformaldehyde is used as fumigant, disinfectant, fungicide, and fixative, and for the preparation of pure formaldehyde. Longer chain-length (high molecular weight) polyoxymethylenes are used as thermoplastic and are known as polyoxymethylene plastic (POM, Delrin). It was used in the past in the discredited Sargenti method of root canal treatment. [2]
[edit] Toxicity
As a formaldehyde releasing agent, paraformaldehyde is a suspected carcinogen. Its acute oral LD50 in rats is 592 mg/kg.
[edit] See also
- Polyoxymethylene plastic
- 1,3,5-Trioxane, the cyclic trimer of formaldehyde
- Polymer
[edit] References
- ^ Yates, J (1973). "Adsorption and decomposition of formaldehyde on tungsten (100) and (111) crystal planes". Journal of Catalysis 30 (2): 260. doi:10.1016/0021-9517(73)90073-0.
- ^ http://www.dentalwatch.org/questionable/sargenti/overview.html
