Paraformaldehyde

Paraformaldehyde

Chembox new
ImageFile = Paraformaldehyd.svg
ImageSize = 150px
IUPACName = Polyoxymethylene
OtherNames =
Section1 = Chembox Identifiers
CASNo = 30525-89-4
PubChem = 24898648
SMILES =
Section2 = Chembox Properties
Formula = (CH2O)n (n = 8 - 100)
MolarMass =
Appearance = white crystalline solid
Density = 0.88 g·cm−3 (20 ºC)
MeltingPt = 120-170 °C
BoilingPt =
Solubility = low
Section3 = Chembox Hazards
EUClass = Toxic (T); Corrosive (C)
ExternalMSDS = [http://msds.chem.ox.ac.uk/PA/paraformaldehyde.html Oxford MSDS]
FlashPt =
Autoignition =

Paraformaldehyde, also known as polyoxymethylene, is the condensation product of formaldehyde with a typical chain length of 8 - 100 units. Long chain-length (high molecular weight) paraformaldehyde is used as a thermoplastic and is known known as polyoxymethylene plastic (POM, "Delrin", polyformaldehyde). Paraformaldehyde commonly has a slight odor of formaldehyde due to decomposition. Paraformaldehyde is a poly-acetal. Paraformaldehyde is used as fumigant, disinfectant, and fungicide, and for the preparation of pure formaldehyde.

Synthesis

Paraformaldehyde forms slowly in formaldehyde solutions (formaline) as a white precipitate, especially if stored in the cold. Formaline 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.

Reactions

Paraformaldehyde can be depolymerized to formaldehyde gas by dry heating and to formaldehyde solution by water in the presence of alkali 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.

Toxicity

As a formaldehyde releasing agent, paraformaldehyde is a suspected carcinogen. Its acute oral LD50 in rats is 592 mg/kg.

See also

* Polyoxymethylene plastic
* 1,3,5-Trioxane, the cyclic trimer of formaldehyde
* Polymer

References


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  • paraformaldehyde — /par euh fawr mal deuh huyd , feuhr /, n. Chem. a white, crystalline polymer of formaldehyde, (HCOH)n, from which it is obtained by evaporation of the aqueous solution: used chiefly as an antiseptic. Also called paraform /par euh fawrm /. [1930… …   Universalium

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