A gas at
room temperature, formaldehyde is colorless and has a characteristic pungent, irritating odor. It is an important precursor to many other materials and chemical compounds. In 1996, the installed capacity for the production of formaldehyde was estimated to be 8.7 million tonnes per year.
[3] Commercial solutions of formaldehyde in water, commonly called
formol, were formerly used as
disinfectants and for preservation of biological specimens. It is commonly used in nail hardeners and/or nail varnish.
Forms of formaldehyde[edit]
Formaldehyde is more complicated than many simple carbon compounds in that it adopts several different forms. One important derivative is the cyclic
trimer metaformaldehyde or
1,3,5-trioxane with the formula (CH
2O)
3. There is also an infinite polymer called
paraformaldehyde. These compounds have similar chemical properties to the molecule CH
2O.
When dissolved in water, formaldehyde forms a hydrate,
methanediol, with the formula H
2C(OH)
2. This also exists in equilibrium with various
oligomers (short polymers), depending on the concentration and temperature. A saturated water solution, of about 40% formaldehyde by volume or 37% by mass, is called "100% formalin". A small amount of
stabilizer, such as
methanol, is usually added to suppress
oxidation and
polymerization. A typical commercial grade formalin may contain 10–12% methanol in addition to various metallic impurities.
Occurrence[edit]
Formaldehyde and its
oligomers and hydrates are rarely encountered in living organisms.
Methanogenesis proceeds via the equivalent
[clarification needed] of formaldehyde, but this one-carbon species is masked as a
methylene group in
methanopterin. Formaldehyde is the primary cause of
methanol's toxicity, since methanol is metabolised into formaldehyde by
alcohol dehydrogenase. Formaldehyde does not accumulate in the environment, because it is broken down within a few hours by sunlight or by bacteria present in soil or water. Humans metabolize formaldehyde quickly, so it does not accumulate, and is converted to
formic acid in the body.
Interstellar formaldehyde[edit]
Formaldehyde was the first
polyatomic organic molecule detected in the
interstellar medium.
[8] Since its initial detection in 1869, it has been observed in many regions of the
galaxy. Because of the widespread interest in interstellar formaldehyde, it has recently been extensively studied, yielding new extragalactic sources.
[9] A proposed mechanism for the formation is the hydrogenation of CO ice, shown below.
[10]- H + CO → HCO
- HCO + H → H2CO (rate constant=9.2×10−3 s−1)[clarification needed]
Formaldehyde appears to be a useful probe for astrochemists due to its low reactivity in the gas phase and to the fact that the 110←111 and 211←212 K-doublet transitions are rather clear.
Synthesis and industrial production[edit]
Formaldehyde is produced industrially by the catalytic oxidation of
methanol. The most common catalysts are
silver metal or a mixture of an
iron and
molybdenum or
vanadium oxides. In the commonly used
formox process, methanol and oxygen react at ca. 250–400 °C in presence of iron oxide in combination with molybdenum and/or vanadium to produce formaldehyde according to the
chemical equation:
[3]- 2 CH3OH + O2 → 2 CH2O + 2 H2O
The silver-based catalyst usually operates at a higher temperature, about 650 °C. Two chemical reactions on it simultaneously produce formaldehyde: that shown above and the
dehydrogenation reaction:
- CH3OH → H2CO + H2
In principle, formaldehyde could be generated by oxidation of
methane, but this route is not industrially viable because the formaldehyde is more easily oxidized than methane.
[3]
Organic chemistry[edit]
Examples of organic synthetic applications[edit]
- 3CH2O + 3H2S → (CH2S)3 + 3H2O
With thanks to Wikipedia
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