Formaldehyde

Names
Preferred IUPAC name Formaldehyde[1]
Systematic IUPAC name Methanal[1]
Other names Methyl aldehyde Methylene glycol (diol forms in aqueous solution) Methylene oxide Formalin (aqueous solution) Formol Carbonyl hydride Methanone Oxomethane
Identifiers
CAS Number	50-00-0 Y
3D model (JSmol)	Interactive image
3DMet	B00018
Beilstein Reference	1209228
ChEBI	CHEBI:16842 Y
ChEMBL	ChEMBL1255 Y
ChemSpider	692 Y
DrugBank	DB03843 Y
ECHA InfoCard	100.000.002
EC Number	200-001-8
E number	E240 (preservatives)
Gmelin Reference	445
IUPHAR/BPS	4196
KEGG	D00017 Y
MeSH	Formaldehyde
PubChem CID	712
RTECS number	LP8925000
UNII	1HG84L3525 Y
UN number	2209
CompTox Dashboard (EPA)	DTXSID7020637
InChI InChI=1S/CH2O/c1-2/h1H2 Y Key: WSFSSNUMVMOOMR-UHFFFAOYSA-N Y InChI=1/CH2O/c1-2/h1H2 Key: WSFSSNUMVMOOMR-UHFFFAOYAT
SMILES C=O
Properties[7]
Chemical formula	CH2O
Molar mass	30.026 g·mol−1
Appearance	Colorless gas
Density	0.8153 g/cm3 (−20 °C)[2] (liquid)
Melting point	−92 °C (−134 °F; 181 K)
Boiling point	−19 °C (−2 °F; 254 K)[2]
Solubility in water	400 g/L
log P	0.350
Vapor pressure	> 1 atm[3]
Acidity (pKa)	13.27 (hydrate)[4][5]
Magnetic susceptibility (χ)	−18.6·10−6 cm3/mol
Dipole moment	2.330 D[6]
Structure
Point group	C2v
Molecular shape	Trigonal planar
Thermochemistry[8]
Heat capacity (C)	35.387 J·mol−1·K−1
Std molar entropy (S⦵298)	218.760 J·mol−1·K−1
Std enthalpy of formation (ΔfH⦵298)	−108.700 kJ·mol−1
Gibbs free energy (ΔfG⦵)	−102.667 kJ·mol−1
Std enthalpy of combustion (ΔcH⦵298)	571 kJ·mol−1
Pharmacology
ATCvet code	QP53AX19 (WHO)
Hazards
GHS labelling:
Pictograms	[9]
Signal word	Danger
Hazard statements	H301, H311, H314, H317, H331, H335, H341, H350, H370[9]
Precautionary statements	P201, P280, P303+P361+P353, P304+P340+P310, P305+P351+P338, P308+P310[9]
NFPA 704 (fire diamond)	4 4 0 COR
Flash point	64 °C (147 °F; 337 K)
Autoignition temperature	430 °C (806 °F; 703 K)
Explosive limits	7–73%
Lethal dose or concentration (LD, LC):
LD50 (median dose)	100 mg/kg (oral, rat)[12]
LC50 (median concentration)	333 ppm (mouse, 2 h) 815 ppm (rat, 30 min)[13]
LCLo (lowest published)	333 ppm (cat, 2 h)[13]
NIOSH (US health exposure limits):
PEL (Permissible)	TWA 0.75 ppm ST 2 ppm (as formaldehyde and formalin)[10][11]
REL (Recommended)	Ca TWA 0.016 ppm C 0.1 ppm [10]
IDLH (Immediate danger)	Ca [10]
Safety data sheet (SDS)	MSDS(Archived)
Related compounds
Related aldehydes	Acetaldehyde Propionaldehyde Butyraldehyde Pentanal Hexanal Heptanal Octanal Nonanal Decanal Octadecanal
Related compounds	Methanol Formic acid Methanimine Ethylene Phosgene Thioformaldehyde
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). Y verify (what is YN ?) Infobox references

Formaldehyde (/fɔːrˈmældɪhaɪd/ ^ⓘ for-MAL-di-hide, US also /fər-/ ^ⓘ fər-) (systematic name methanal) is an organic compound with the chemical formula CH₂O and structure H−CHO, more precisely H₂C=O. The compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde. It is stored as aqueous solutions (formalin), which consists mainly of the hydrate CH₂(OH)₂. It is the simplest of the aldehydes (R−CHO). As a precursor to many other materials and chemical compounds, in 2006 the global production of formaldehyde was estimated at 12 million tons per year.^[14] It is mainly used in the production of industrial resins, e.g., for particle board and coatings. Small amounts also occur naturally.

Formaldehyde is classified as a carcinogen^{[note 1]} and can cause respiratory and skin irritation upon exposure.^[15]

Forms

Formaldehyde is more complicated than many simple carbon compounds in that it adopts several diverse forms. These compounds can often be used interchangeably and can be interconverted.

• Molecular formaldehyde. A colorless gas with a characteristic pungent, irritating odor. It is stable at about 150 °C, but polymerizes when condensed to a liquid.
• 1,3,5-Trioxane, with the formula (CH₂O)₃. It is a white solid that dissolves without degradation in organic solvents. It is a trimer of molecular formaldehyde.
• Paraformaldehyde, with the formula HO(CH₂O)_nH. It is a white solid that is insoluble in most solvents.
• Methanediol, with the formula CH₂(OH)₂. This compound 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.

"Formaldehyde" was first used as a generic trademark in 1893 following a previous trade name, "formalin".^[16]

• Main forms of formaldehyde
• 
  Monomeric formaldehyde (subject of this article)
• 
  Trioxane is a stable cyclic trimer of formaldehyde.
• 
  Paraformaldehyde is a common form of formaldehyde for industrial applications.
• 
  Methanediol, the predominant species in dilute aqueous solutions of formaldehyde

Structure and bonding

Molecular formaldehyde contains a central carbon atom with a double bond to the oxygen atom and a single bond to each hydrogen atom. This structure is summarised by the condensed formula H₂C=O.^[17] The molecule is planar, Y-shaped and its molecular symmetry belongs to the C_2v point group.^[18] The precise molecular geometry of gaseous formaldehyde has been determined by gas electron diffraction^[17][19] and microwave spectroscopy.^[20][21] The bond lengths are 1.21 Å for the carbon–oxygen bond^{[17][19][20][21][22]} and around 1.11 Å for the carbon–hydrogen bond,^{[17][19][20][21]} while the H–C–H bond angle is 117°,^[20][21] close to the 120° angle found in an ideal trigonal planar molecule.^[17] Some excited electronic states of formaldehyde are pyramidal rather than planar as in the ground state.^[22]

Occurrence

Processes in the upper atmosphere contribute up to 90% of the total formaldehyde in the environment.^{[citation needed]} Formaldehyde is an intermediate in the oxidation (or combustion) of methane, as well as of other carbon compounds, e.g. in forest fires, automobile exhaust, and tobacco smoke. When produced in the atmosphere by the action of sunlight and oxygen on atmospheric methane and other hydrocarbons, it becomes part of smog. Formaldehyde has also been detected in outer space.

Formaldehyde and its adducts are ubiquitous in nature. Food may contain formaldehyde at levels 1–100 mg/kg.^[23] Formaldehyde, formed in the metabolism of the amino acids serine and threonine, is found in the bloodstream of humans and other primates at concentrations of approximately 50 micromolar.^[24] Experiments in which animals are exposed to an atmosphere containing isotopically labeled formaldehyde have demonstrated that even in deliberately exposed animals, the majority of formaldehyde-DNA adducts found in non-respiratory tissues are derived from endogenously produced formaldehyde.^[25]

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, converting it to formic acid, so it does not accumulate.^[26][27] It nonetheless presents significant health concerns, as a contaminant.

Interstellar formaldehyde

Formaldehyde appears to be a useful probe in astrochemistry due to prominence of the 1₁₀←1₁₁ and 2₁₁←2₁₂ K-doublet transitions. It was the first polyatomic organic molecule detected in the interstellar medium.^[28] Since its initial detection in 1969, it has been observed in many regions of the galaxy. Because of the widespread interest in interstellar formaldehyde, it has been extensively studied, yielding new extragalactic sources.^[29] A proposed mechanism for the formation is the hydrogenation of CO ice:^[30]

H + CO → HCO

HCO + H → CH₂O

HCN, HNC, H₂CO, and dust have also been observed inside the comae of comets C/2012 F6 (Lemmon) and C/2012 S1 (ISON).^[31][32]

Synthesis and industrial production

Laboratory synthesis

Formaldehyde was first reported in 1859 by the Russian chemist Aleksandr Butlerov (1828–1886).^[33] In his paper, Butlerov referred to formaldehyde as "dioxymethylen" (methylene dioxide) because his empirical formula for it was incorrect (C₄H₄O₄). It was conclusively identified by August Wilhelm von Hofmann, who first announced the production of formaldehyde by passing methanol vapor in air over hot platinum wire.^[34][35] With modifications, Hoffmann's method remains the basis of the present day industrial route.

Solution routes to formaldehyde also entail oxidation of methanol or methyl iodide.^[36]

Industry

Formaldehyde is produced industrially by the catalytic oxidation of methanol. The most common catalysts are silver metal, iron(III) oxide,^[37] iron molybdenum oxides with a molybdenum-enriched surface,^[38] or vanadium oxides. In the commonly used formox process, methanol and oxygen react at c. 250–400 °C in presence of iron oxide in combination with molybdenum and/or vanadium to produce formaldehyde according to the chemical equation:^[39]

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 → CH₂O + H₂

In principle, formaldehyde could be generated by oxidation of methane, but this route is not industrially viable because the methanol is more easily oxidized than methane.^[39]

Biochemistry

Formaldehyde is produced via several enzyme-catalyzed routes.^[40] Living beings, including humans, produce formaldehyde as part of their metabolism. Formaldehyde is key to several bodily functions (e.g. epigenetics^[24]), but its amount must also be tightly controlled to avoid self-poisioning.^[41]

• Serine hydroxymethyltransferase can decompose serine into formaldehyde and glycine, according to this reaction: HOCH₂CH(NH₂)CO₂H → CH₂O + H₂C(NH₂)CO₂H.
• methylotrophic microbes convert methanol into formaldehyde and energy via methanol dehydrogenase: CH₃OH → CH₂O + 2e⁻ + 2H⁺
• Other routes to formaldehyde include oxidative demethylations, semicarbazide-sensitive amine oxidases, dimethylglycine dehydrogenases, lipid peroxidases, P450 oxidases, and N-methyl group demethylases.^[40]

Formaldehyde is catabolized by alcohol dehydrogenase ADH5 and aldehyde dehydrogenase ALDH2.^[42]

Organic chemistry

Formaldehyde is a building block in the synthesis of many other compounds of specialised and industrial significance. It exhibits most of the chemical properties of other aldehydes but is more reactive.

Polymerization and hydration

Monomeric CH₂O is a gas and is rarely encountered in the laboratory. Aqueous formaldehyde, unlike some other small aldehydes (which need specific conditions to oligomerize through aldol condensation) oligomerizes spontaneously at a common state. The trimer is 1,3,5-trioxane ((CH₂O)₃) is typical oligomer. Many cyclic oligomers of other sizes have been isolated. Similarly, formaldehyde hydrates to give the geminal diol methanediol, which condenses further to form hydroxy-terminated oligomers HO(CH₂O)_nH. The polymer is called paraformaldehyde. The higher concentration of formaldehyde—the more equilibrium shifts towards polymerization. Diluting with water or increasing the solution temperature, as well as adding alcohols (such as methanol or ethanol) lowers that tendency.

Gaseous formaldehyde polymerizes at active sites on vessel walls, but the mechanism of the reaction is unknown.^[43] Small amounts of hydrogen chloride (or boron trifluoride, or stannic chloride) present in gaseous formaldehyde provide the catalytic effect and make the polymerization rapid.^[44]

Oxidation and reduction

It is readily oxidized by atmospheric oxygen into formic acid. For this reason, commercial formaldehyde is typically contaminated with formic acid. Formaldehyde can be hydrogenated into methanol.

In the Cannizzaro reaction, formaldehyde and base react to produce formic acid and methanol, a disproportionation reaction.

Hydroxymethylation and chloromethylation

Formaldehyde reacts with many compounds, resulting in hydroxymethylation:

X-H + CH₂O → X-CH₂OH

(X = R₂N, RC(O)NR', SH). The resulting hydroxymethyl derivatives typically react further. Thus, amines give hexahydro-1,3,5-triazines:

3 RNH₂ + 3 CH₂O → (RNCH₂)₃ + 3 H₂O

Similarly, when combined with hydrogen sulfide, it forms trithiane:^[45]

3 CH₂O + 3 H₂S → (CH₂S)₃ + 3 H₂O

In the presence of acids, it participates in electrophilic aromatic substitution reactions with aromatic compounds resulting in hydroxymethylated derivatives:

ArH + CH₂O → ArCH₂OH

When conducted in the presence of hydrogen chloride, the product is the chloromethyl compound, as described in the Blanc chloromethylation. If the arene is electron-rich, as in phenols, elaborate condensations ensue. With 4-substituted phenols one obtains calixarenes.^[46] Phenol results in polymers. Zdroj:https://en.wikipedia.org?pojem=Formaldehyde
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