Paraformaldehyde

Structural formula
General
Surname	Paraformaldehyde
other names	Polyoxymethylene Paraform p -formaldehyde Polyformaldehyde
CAS number	30525-89-4
Monomer	formaldehyde
Molecular formula of the repeating unit	CH 2 O
Molar mass of the repeating unit	30.03 g mol −1
Brief description	white solid with a characteristic odor
properties
Physical state	firmly
density	1.39 g cm −3 (20 ° C)
Melting point	approx. 130 ° C (closed vessel) 120–170 ° C
solubility	poorly soluble in water (20 ° C)
safety instructions
GHS labeling of hazardous substances danger H and P phrases H: 228-302 + 332-315-317-318-335-350 P: 201-210-280-302 + 352-305 + 351 + 338
Toxicological data	592 mg kg −1 ( LD 50 ,  rat ,  oral ) 1.07 mg l −1 4 h ( LC 50 ,  rat ,  inh. ) 10,000 mg kg −1 ( LD Lo ,  rat ,  transdermal )
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Paraformaldehyde (PFA) is the short-chain polymer of formaldehyde ; the degree of polymerisation is 8–100. It is a white powder that breaks down into formaldehyde again when the pH value is low or when it is heated. The breakdown takes place via the end groups. If these are protected by esterification or etherification , a stable plastic is obtained, the polyoxymethylene .

When paraformaldehyde is heated in water or an aqueous buffer solution, it disintegrates and a formaldehyde solution is obtained. This is sometimes referred to as "paraformaldehyde solution" to differentiate it from formaldehyde solutions that are made by diluting with formalin , a concentrated formaldehyde solution that also contains methanol for stabilization . Strictly speaking, however, the term paraformaldehyde solution is incorrect because the polymer is insoluble in water. This solution is used in biology for the fixation of tissues or cell cultures , usually in concentrations between 0.5% and 4%, buffered to a neutral pH value. The effect is based on the reversible cross-linking of proteins .

Paraformaldehyde is harmful to health and is suspected of being carcinogenic. The oral LD ₅₀ value for a rat is 592 mg / kg. The vapor pressure at 25 ° C is 2h Pa . The maximum workplace concentration is 0.3 ml · m ⁻³ or 0.37 mg · m ⁻³ .

In preparative chemistry, paraformaldehyde can be used for formylation reactions and syntheses derived therefrom, e.g. B. Mannich reaction , Blanc reaction (“chloromethylation”).

See also

• Polyoxymethylene - chemically identical engineering plastic
• paraldehyde

Individual evidence

1. ↑ ^{a b c d e f g h i} Entry on paraformaldehyde in the GESTIS substance database of the IFA , accessed on July 30, 2017(JavaScript required) .
2. ↑ ^{a b c d} Data sheet paraformaldehyde (PDF) from Merck , accessed on April 5, 2014.
3. ^ Howard M. Shapiro: Practical Flow Cytometry. 4th Edition, John Wiley & Sons, 2005. ISBN 9780471434030 . P. 304.
4. ↑ Alan Michael Tartakoff: Methods in Cell Biology, Volume 31: Vesicular Transport, Part A: Vesicular transport. Part 1, Academic Press, 1989. ISBN 9780080859293 . P. 444.

Web links

• ChemDAT® Germany - The Merck chemistry databases