Paraformaldehyde: Difference between revisions

{{Distinguish|Paraldehyde}}

| Verifiedfields = changed

| Watchedfields = changed

| verifiedrevid = 446640299

|Section1={{Chembox Identifiers

| EINECS = 608-494-5

| UNII_Ref = {{fdacite|correct|FDA}}

| UNII = Y19UC83H8E

| UNNumber = 2213

| PubChem =

| ChemSpiderID_Ref = {{chemspidercite|changed|chemspider}}

| ChemSpiderID = none

|Section2={{Chembox Properties

| Appearance = White powder with formaldehyde-like odour

| Density = 1.46 g/cm³

| MeltingPtC = 120

| VaporPressure = 1.579 kPa

| Solubility = slightly soluble}}

|Section3={{Chembox Hazards

| GHS_ref=<ref>{{cite web |title=C&L Inventory |url=https://echa.europa.eu/information-on-chemicals/cl-inventory-database/-/discli/details/10166 |website=echa.europa.eu |access-date=27 December 2021}}</ref>

| GHSPictograms = {{GHS02}}{{GHS08}}

| GHSSignalWord = Danger

| HPhrases = {{H-phrases|228|302|315|317|318|332|334|351}}

| PPhrases = {{P-phrases|}}

| ExternalSDS = [https://www.fishersci.com/store/msds?partNumber=O4042500&productDescription=PARAFORMALDEHYDE+R+500G&vendorId=VN00033897&countryCode=US&language=en Fisher Scientific]

| FlashPtC = 71

| AutoignitionPtC = 300

| LD50 = 800 mg/kg (rat, oral)

| LC50 = 1070 mg/m³ (rat, 4h)

| ExploLimits = 7.0% (low), 73% (high)

| NFPA-H = 3

| NFPA-F = 2

| NFPA-I = 1

}}

'''Paraformaldehyde''' ('''PFA''') is the smallest [[polyoxymethylene]], the [[polymerization reaction|polymerization]] 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]].

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 [[Polyoxymethylene|polyformaldehyde]]. A small amount of [[methanol]] is often added as a [[Stabilizer (chemistry)|stabilizer]] to limit the extent of [[polymerization]].

Paraformaldehyde can be [[depolymerization|depolymerized]] to formaldehyde gas by dry heating<ref>{{cite journal | doi = 10.1016/0021-9517(73)90073-0 | title = Adsorption and decomposition of formaldehyde on tungsten (100) and (111) crystal planes | year = 1973 | last1 = Yates | first1 = J | journal = [[Journal of Catalysis]] | volume = 30 | page = 260 | issue = 2 }}</ref> and to formaldehyde solution by [[water (molecule)|water]] in the presence of a base, an acid or heat. The high purity formaldehyde solutions obtained in this way are used as a [[fixation (histology)|fixative]] for [[microscopy]] and [[histology]].

The resulting formaldehyde gas from dry heating paraformaldehyde is flammable.

Once paraformaldehyde is depolymerized, the resulting formaldehyde may be used as a [[fumigant]], [[disinfectant]], [[fungicide]], and [[fixation (histology)|fixative]]. Longer chain-length (high molecular weight) polyoxymethylenes are used as a [[thermoplastic]] and are known as [[polyoxymethylene]] plastic (POM, ''Delrin''). It was used in the past in the discredited Sargenti method of [[root canal treatment]].<ref>{{Cite web|url=http://www.dentalwatch.org/questionable/sargenti/overview.html|title = Be Wary of Sargenti Root Canal Treatment &#124; Quackwatch|date = May 2018}}</ref>

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. In histology and pathology specimens preparation, usually, the fixation step is performed using 10% Neutral Buffered Formalin (4% formaldehyde) for, at least, 24 hours.

Paraformaldehyde is also used to crosslink proteins to DNA, as used in ChIP ([[chromatin immunoprecipitation]]) which is a technique to determine which part of DNA certain proteins are binding to.

Paraformaldehyde can be used as a substitute of aqueous formaldehyde to produce the resinous binding material, which is commonly used together with [[melamine]], [[phenol]] or other reactive agents in the manufacturing of [[particle board]], medium density [[fiberboard]] and [[plywood]].<ref>{{Cite web|url=http://dovechem.co.id/en/paraformaldehyde-3|title = Paraformaldehyde - Dover Chemical}}</ref>

== Toxicity ==

As a formaldehyde releasing agent, paraformaldehyde is a potential [[carcinogen]].<ref>{{cite journal|last1=Cogliano|first1=Vincent|last2=Grosse|first2=Yann|last3=Baan|first3=Robert|last4=Straif|first4=Kurt|last5=Secretan|first5=Béatrice|last6=Ghissassi|first6=Fatiha El|title=Advice on formaldehyde and glycol ethers|journal=The Lancet Oncology|date=September 2004|volume=5|issue=9|page=528|doi=10.1016/S1470-2045(04)01562-1|pmid=15384217}}</ref> Its acute oral [[median lethal dose]] in rats is 592&nbsp;mg/kg.<ref>{{cite web|title=MSDS - 158127 SAFETY DATA SHEET - Paraformaldehyde|url=https://www.sigmaaldrich.com/US/en/product/sial/158127

|publisher=SIGMA-ALDRICH|access-date=15 February 2022}}</ref>

== See also ==

* [[1,3,5-Trioxane]] (metaformaldehyde), the cyclic trimer of formaldehyde

{{Reflist}}

{{Authority control}}

[[Category:Polyethers]]

[[Category:Hemiacetals]]