Paraformaldehyde
Encyclopedia
Paraformaldehyde 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
.
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
.
to formaldehyde gas by dry heating 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.
, and fixation
, 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.
Polyoxymethylene
Polyoxymethylene , also known as acetal, polyacetal, and polyformaldehyde, is an engineering thermoplastic used in precision parts that require high stiffness, low friction and excellent dimensional stability....
, it is the condensation reaction
Condensation reaction
A condensation reaction is a chemical reaction in which two molecules or moieties combine to form one single molecule, together with the loss of a small molecule. When this small molecule is water, it is known as a dehydration reaction; other possible small molecules lost are hydrogen chloride,...
product of formaldehyde
Formaldehyde
Formaldehyde is an organic compound with the formula CH2O. It is the simplest aldehyde, hence its systematic name methanal.Formaldehyde is a colorless gas with a characteristic pungent odor. It is an important precursor to many other chemical compounds, especially for polymers...
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
Acetal
An acetal is a molecule with two single-bonded oxygen atoms attached to the same carbon atom.Traditional usages distinguish ketals from acetals...
.
Synthesis
Paraformaldehyde forms slowly in aqueous formaldehydeFormaldehyde
Formaldehyde is an organic compound with the formula CH2O. It is the simplest aldehyde, hence its systematic name methanal.Formaldehyde is a colorless gas with a characteristic pungent odor. It is an important precursor to many other chemical compounds, especially for polymers...
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
Methanol
Methanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with the formula CH3OH . It is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a distinctive odor very similar to, but slightly sweeter than, ethanol...
is often added as a stabilizer
Stabilizer (chemistry)
In chemistry a stabilizer is a chemical which tends to inhibit the reaction between two or more other chemicals. It can be thought of as the antonym to a catalyst...
to limit the extent of polymerization
Polymerization
In polymer chemistry, polymerization is a process of reacting monomer molecules together in a chemical reaction to form three-dimensional networks or polymer chains...
.
Reactions
Paraformaldehyde can be depolymerizedDepolymerization
Depolymerization is the process of converting a polymer into a monomer or a mixture of monomers.Thioglycolysis, thiolysis and phloroglucinolysis are reactions used to study condensed tannins by means of their depolymerisation. Thioglycolysis is also used to study lignin....
to formaldehyde gas by dry heating 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
Fixation (histology)
In the fields of histology, pathology, and cell biology, fixation is a chemical process by which biological tissues are preserved from decay, thereby preventing autolysis or putrefaction...
for microscopy
Microscopy
Microscopy is the technical field of using microscopes to view samples and objects that cannot be seen with the unaided eye...
and histology
Histology
Histology is the study of the microscopic anatomy of cells and tissues of plants and animals. It is performed by examining cells and tissues commonly by sectioning and staining; followed by examination under a light microscope or electron microscope...
.
Paraformaldehyde is flammable as it decomposes in the heat into the flammable gas formaldehyde.
Uses
Paraformaldehyde is used as fumigant, disinfectant, fungicideFungicide
Fungicides are chemical compounds or biological organisms used to kill or inhibit fungi or fungal spores. Fungi can cause serious damage in agriculture, resulting in critical losses of yield, quality and profit. Fungicides are used both in agriculture and to fight fungal infections in animals...
, and fixation
Fixation
Fixation may refer to the following:In science:*Fixation , the state in which an individual becomes obsessed with an attachment to another human, an animal, or an inanimate object...
, and for the preparation of pure formaldehyde. Longer chain-length (high molecular weight) polyoxymethylenes are used as thermoplastic
Thermoplastic
Thermoplastic, also known as a thermosoftening plastic, is a polymer that turns to a liquid when heated and freezes to a very glassy state when cooled sufficiently...
and are known as polyoxymethylene plastic (POM, Delrin). It was used in the past in the discredited Sargenti method of root canal treatment.
Toxicity
As a formaldehyde releasing agent, paraformaldehyde is a suspected carcinogen. Its acute oral in rats is 592 mg/kg.See also
- Polyoxymethylene plastic
- 1,3,5-Trioxane1,3,5-Trioxane1,3,5-Trioxane, sometimes also called trioxin, is a chemical compound with molecular formula C3H6O3. It is a stable cyclic trimer of formaldehyde, and one of the two trioxane isomers; its molecular backbone consists of a six membered ring with three carbon atoms alternating with three oxygen...
, the cyclic trimer of formaldehyde - PolymerPolymerA polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...