Paraformaldehyde

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Paraformaldehyde
Identifiers
CAS number30525-89-4 YesY
PubChem24898648
Properties
Molecular formulaOH(CH2O)nH (n = 8 - 100)
Appearancewhite crystalline solid
Density1.42 g·cm−3 (25 °C)
Melting point

120 °C

Solubility in waterlow
Hazards
MSDSOxford MSDS
EU classificationToxic (T); Corrosive (C)
 YesY (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references
 
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Paraformaldehyde
Identifiers
CAS number30525-89-4 YesY
PubChem24898648
Properties
Molecular formulaOH(CH2O)nH (n = 8 - 100)
Appearancewhite crystalline solid
Density1.42 g·cm−3 (25 °C)
Melting point

120 °C

Solubility in waterlow
Hazards
MSDSOxford MSDS
EU classificationToxic (T); Corrosive (C)
 YesY (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Paraformaldehyde (PFA) is the smallest polyoxymethylene, the polymerization product of formaldehyde with a typical degree of polymerization of 8–10 units. Paraformaldehyde commonly has a slight odor of formaldehyde due to decomposition. Paraformaldehyde is a poly-acetal.

Synthesis[edit source | edit]

Paraformaldehyde forms slowly in aqueous formaldehyde solutions 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 small amount of methanol is often added as a stabilizer to limit the extent of polymerization.

Reactions[edit source | edit]

Paraformaldehyde can be depolymerized to formaldehyde gas by dry heating[1] and to formaldehyde solution by water in the presence of a base or heat. The very pure formaldehyde solutions obtained in this way are used as a fixative for microscopy and histology.

The resulting formaldehyde gas from dry heating paraformaldehyde is flammable.

Uses[edit source | edit]

Once paraformaldehyde is depolymerized, the resulting formaldehyde may be used as a fumigant, disinfectant, fungicide, and fixative. 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]

Paraformaldehyde is not a fixative--it must be depolymerized to formaldehyde in solution. In cell culture, a typical formaldehyde fixing procedure would involve using a 4% formaldehyde solution in phosphate buffered saline (PBS) on ice for 10 minutes.

Toxicity[edit source | edit]

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

See also[edit source | edit]

References[edit source | edit]

  1. ^ 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. 
  2. ^ http://www.dentalwatch.org/questionable/sargenti/overview.html