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Dimethoxymethane
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| Names | |
|---|---|
| Preferred IUPAC name
Dimethoxymethane | |
| Other names
Formal
Formaldehyde dimethyl ether | |
| Identifiers | |
3D model (JSmol)
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| 1697025 | |
| ChEBI | |
| ChEMBL | |
| ChemSpider | |
| ECHA InfoCard | 100.003.378 |
| EC Number |
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| 100776 | |
| MeSH | Dimethoxymethane |
PubChem CID
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| RTECS number |
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| UNII | |
| UN number | 1234 |
CompTox Dashboard (EPA)
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| Properties | |
| C3H8O2 | |
| Molar mass | 76.095 g·mol−1 |
| Appearance | Colorless liquid[1] |
| Odor | Chloroform-like[1] |
| Density | 0.8593 g cm−3 (at 20 °C)[1] |
| Melting point | −105 °C (−157 °F; 168 K)[1][3] |
| Boiling point | 42 °C (108 °F; 315 K)[1][3] |
| 33% (20 °C)[2][clarification needed] | |
| Vapor pressure | 330 mmHg (20 °C)[2] |
| −47.3·10−6 cm3/mol | |
| Hazards | |
| GHS labelling: | |
 
| |
| Danger | |
| H225, H315, H319, H335 | |
| P210, P233, P240, P241, P242, P243, P261, P264, P271, P280, P302+P352, P303+P361+P353, P304+P340, P305+P351+P338, P312, P321, P332+P313, P337+P313, P362, P370+P378, P403+P233, P403+P235, P405, P501 | |
| Flash point | −18 °C (0 °F; 255 K) |
| Explosive limits | 2.2–13.8%[2] |
| Lethal dose or concentration (LD, LC): | |
LD50 (median dose)
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5708 mg/kg (rabbit, oral)[4] |
LC50 (median concentration)
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18000 ppm (mouse, 7 hr) 15000 ppm (rat) 18354 ppm (mouse, 7 hr)[4] |
| NIOSH (US health exposure limits): | |
PEL (Permissible)
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TWA 1000 ppm (3100 mg/m3)[2] |
REL (Recommended)
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TWA 1000 ppm (3100 mg/m3)[2] |
IDLH (Immediate danger)
|
2200 ppm[2] |
| Related compounds | |
Related Ethers
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Dimethoxyethane |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Dimethoxymethane, also called methylal, is a colorless flammable liquid with a low boiling point, low viscosity and excellent dissolving power. It has a chloroform-like odor and a pungent taste. It is the dimethyl acetal of formaldehyde. Dimethoxymethane is soluble in three parts water[clarification needed] and miscible with most common organic solvents.
Synthesis and structure
[edit]It can be manufactured by oxidation of methanol or by the reaction of formaldehyde with methanol. In aqueous acid, it is hydrolyzed back to formaldehyde and methanol.
Due to the anomeric effect, dimethoxymethane has a preference toward the gauche conformation with respect to each of the C–O bonds, instead of the anti conformation. Since there are two C–O bonds, the most stable conformation is gauche-gauche, which is around 7 kcal/mol more stable than the anti-anti conformation, while the gauche-anti and anti-gauche are intermediate in energy.[5] Since it is one of the smallest molecules exhibiting this effect, which has great interest in carbohydrate chemistry, dimethoxymethane is often used for theoretical studies of the anomeric effect.
Applications
[edit]Industrially, it is primarily used as a solvent and in the manufacture of perfumes, resins, adhesives, paint strippers and protective coatings. Another application is as a gasoline-additive for increasing octane number. Dimethoxymethane can also be used for blending with diesel. [6]
Reagent in organic synthesis
[edit]Another useful application of dimethoxymethane is to protect alcohols with a methoxymethyl (MOM) ether in organic synthesis. Dimethoxymethane can be activated with phosphorus pentoxide in dichloromethane or chloroform.[7] This method is preferred to the use of chloromethyl methyl ether (MOMCl). Phenols can also be MOM-protected using dimethoxymethane, p-toluenesulfonic acid.[8] Alternatively, MOMCl can be generated as a solution by treating dimethoxymethane with an acyl chloride in the presence of a Lewis acid catalyst like zinc bromide:
- MeOCH2OMe + RC(=O)Cl → MeOCH2Cl + RC(=O)(OMe)).
Unlike the classical procedure, which uses formaldehyde and hydrogen chloride as starting materials, the highly carcinogenic side product bis(chloromethyl) ether is not generated.[9]
References
[edit]- ^ a b c d e Merck Index, 11th Edition, 5936
- ^ a b c d e f NIOSH Pocket Guide to Chemical Hazards. "#0396". National Institute for Occupational Safety and Health (NIOSH).
- ^ a b International Chemical Safety Card 1152
- ^ a b "Methylal". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
- ^ Carey, Francis A.; Sundberg, Richard J. (2007). Advanced organic chemistry (5th ed.). New York: Springer. ISBN 9780387448978. OCLC 154040953.
- ^ Shrestha, Krishna P.; Eckart, Sven; Elbaz, Ayman M.; Giri, Binod R.; Fritsche, Chris; Seidel, Lars; Roberts, William L.; Krause, Hartmut; Mauss, Fabian (2020). "A comprehensive kinetic model for dimethyl ether and dimethoxymethane oxidation and NO interaction utilizing experimental laminar flame speed measurements at elevated pressure and temperature". Combustion and Flame. 218: 57–74. doi:10.1016/j.combustflame.2020.04.016. hdl:10754/662921.
- ^ Wuts, P. G. M.; Greene, T.W. (2006). Greene's Protective Groups in Organic Synthesis. NY: J. Wiley. doi:10.1002/0470053488. ISBN 9780470053485.
- ^ Yardley, John P.; Fletcher, Horace (1976). "Introduction of the Methoxymethyl Ether Protecting Group". Synthesis. 1976 (04): 244–244. doi:10.1055/s-1976-24000.
- ^ Berliner, Martin; Belecki., Katherine (2007). "Synthesis of alpha-Halo Ethers from Symmetric Acetals and in situ Methoxymethylation of an Alcohol". Organic Syntheses. 84: 102. doi:10.15227/orgsyn.084.0102.
External links
[edit]- NIOSH Pocket Guide to Chemical Hazards. "#0396". National Institute for Occupational Safety and Health (NIOSH).
Dimethoxymethane
View on Grokipediafrom Grokipedia
Properties
Physical properties
Dimethoxymethane is a colorless, volatile liquid with a chloroform-like odor.[1][7] Its molecular formula is C₃H₈O₂, and it has a molecular weight of 76.10 g/mol.[3] The compound has a melting point of −105 °C and a boiling point of 42 °C.[7] Its density is 0.86 g/cm³ at 20 °C, and the refractive index is 1.353 at 20 °C.[1][8] Dimethoxymethane exhibits low viscosity of 0.32 mPa·s at 25 °C and high vapor pressure of approximately 53 kPa at 25 °C, properties that enhance its utility as a solvent.[9][10] It is miscible with many organic solvents, including alcohols, ethers, and hydrocarbons, but shows limited solubility in water at about 28.5 g/100 mL at 20 °C.[7][1]Chemical properties
Dimethoxymethane possesses the molecular formula C₃H₈O₂ and the structural formula (CH₃O)₂CH₂, making it the dimethyl acetal derived from formaldehyde and methanol.[1] The central methylene carbon exhibits sp³ hybridization, resulting in tetrahedral geometry with approximate bond angles of 110.8° for O-C-O and 112.4° for the C-O-C linkages. This configuration contributes to a dipole moment of 0.99 D, reflecting the polar nature of the ether linkages. As an acetal, dimethoxymethane demonstrates characteristic reactivity typical of this functional group, including its role in protecting carbonyl compounds through acetal formation, which masks the reactivity of aldehydes or ketones under basic or nucleophilic conditions. It undergoes acid-catalyzed hydrolysis in aqueous media, reverting to formaldehyde and methanol according to the equation (CH₃O)₂CH₂ + H₂O → HCHO + 2 CH₃OH.[1] This process is pH-dependent, with stability maintained at neutral or basic pH but rapid decomposition under acidic conditions. Thermally, it remains stable up to approximately 350 °C in inert environments, though oxidative decomposition can initiate at lower temperatures around 100 °C.[11][12] Spectroscopic characterization confirms its structure, with infrared (IR) absorption bands including a C-H stretching vibration at around 2830 cm⁻¹ for the methoxy groups and a strong C-O stretching band near 1100 cm⁻¹.[13] In the ¹H nuclear magnetic resonance (NMR) spectrum, the methylene protons appear as a singlet at 4.44 ppm (2H), while the methyl protons resonate as a singlet at 3.20 ppm (6H), consistent with the symmetric environment of the acetal moiety.[14]Production
Industrial production
Dimethoxymethane is primarily produced industrially through a two-step process involving the oxidation of methanol to formaldehyde followed by acid-catalyzed acetalization with additional methanol.[4] This method leverages the availability of methanol as a low-cost feedstock and established catalytic technologies for large-scale operation.[15] In the first step, methanol is oxidized to formaldehyde in a fixed-bed reactor using air as the oxidant. The reaction, CH₃OH + ½O₂ → HCHO + H₂O, employs either silver catalysts for high-temperature operation at 600–700 °C or iron-molybdate catalysts (such as in the Formox process) at 250–400 °C, achieving near-complete methanol conversion.[16][17] The gaseous formaldehyde product is then absorbed into aqueous solution or directly fed to the next stage. In the second step, formaldehyde reacts with excess methanol under acidic conditions to form the acetal: HCHO + 2 CH₃OH ⇌ (CH₃O)₂CH₂ + H₂O. This equilibrium-limited reaction is catalyzed by sulfuric acid or solid acid catalysts like ion-exchange resins and conducted at 50–100 °C in continuous reactors to favor product formation.[18] To drive the reversible acetalization toward completion, water is continuously removed via distillation or azeotropic separation, enabling overall process yields of approximately 90%.[18] The crude dimethoxymethane is purified by fractional distillation, exploiting its favorable boiling point relative to methanol and water. This integrated approach ensures high efficiency and minimal byproduct formation in commercial plants. Global production of dimethoxymethane is estimated at 200,000–300,000 metric tons annually as of 2023, with major capacity concentrated in Europe and Asia. Key producers include Lambiotte in Belgium, which specializes in acetal-based chemicals, and Kuraray in Japan, leveraging integrated methanol derivative facilities.[19] In 2023, several manufacturers invested in upgrading production facilities, and Kuraray introduced more sustainable processes as of 2022.[20] Market growth is driven by demand in solvents and coatings, though exact volumes vary with regional feedstock costs. Recent research since 2018 has focused on greener alternatives, such as direct one-pot synthesis from syngas (CO + H₂) or partial oxidation of methanol using bifunctional catalysts that combine metal sites (e.g., Cu/ZnO for formaldehyde generation) with acid sites for in situ acetalization. These approaches aim to reduce energy intensity and emissions by eliminating intermediate purification, with promising results in pilot-scale demonstrations.[21][4]Laboratory synthesis
Dimethoxymethane is commonly prepared in laboratory settings through the acid-catalyzed acetalization of formaldehyde precursors with methanol. A standard method employs trioxane or paraformaldehyde as the formaldehyde source, reacted with excess methanol in the presence of an acidic catalyst such as Amberlyst 15 resin or p-toluenesulfonic acid. For instance, using Amberlyst 15 at 5 wt% loading, a methanol-to-trioxane molar ratio of 2.2:1, and 1,4-dioxane as solvent at 70 °C for 3 hours yields approximately 62% dimethoxymethane.[22] Alternatively, p-toluenesulfonic acid catalyzes the condensation under reflux conditions near 65 °C, often achieving high conversions due to the equilibrium-driven nature of the reaction.[23] Alternative routes focus on direct synthesis from methanol via oxidative coupling, bypassing separate formaldehyde generation. This involves gas-phase partial oxidation of methanol with molecular oxygen over bifunctional metal-acid catalysts, such as vanadium oxide supported on titania (V₂O₅/TiO₂) or heteropolyacids like silicotungstic acid, at temperatures of 150–200 °C and atmospheric pressure. These catalysts facilitate sequential dehydrogenation to formaldehyde intermediates and acetalization, with selectivities exceeding 80% at moderate conversions (e.g., 25–50% methanol conversion).[4][24] Emerging photocatalytic methods enable synthesis from CO₂ and H₂ through syngas-like intermediates in methanol solvent, using catalysts like Ag/W-modified blue TiO₂ under visible light irradiation, coupling CO₂ reduction with methanol oxidation to form dimethoxymethane with improved atom economy.[25] Purification typically involves vacuum distillation under an inert atmosphere to minimize hydrolysis back to formaldehyde and methanol, followed by analytical verification using gas chromatography-mass spectrometry (GC-MS) to confirm purity and identify impurities.[4] Modern laboratory variants emphasize efficiency through catalyst-free or low-catalyst approaches, such as neutral condensation using a molecularly defined Ni(II)-NNN pincer complex (2 mol%) with paraformaldehyde and methanol under mild conditions, delivering excellent yields in shorter times compared to traditional acidic methods.[26]Applications
Solvent applications
Dimethoxymethane serves as a versatile solvent in various industrial processes, leveraging its low boiling point, volatility, and ability to dissolve a range of organic compounds. Its miscibility with many organics makes it suitable for applications requiring efficient dissolution without residual effects. Primarily, it accounts for the largest share of dimethoxymethane's market demand, exceeding 35% of total applications as of 2024, driven by its relatively low toxicity profile compared to traditional halogenated solvents.[27] In polymer processing, dimethoxymethane functions as an effective solvent for polyacetals, resins, and other polymers used in coatings and adhesives. Its low viscosity and non-polar characteristics enable it to control formulation consistency, facilitate smooth application, and promote uniform film formation in paints, varnishes, lacquers, and adhesive systems such as spray and laminating types. This results in enhanced performance, quick drying times, and cost efficiency in manufacturing surface finishes and bonding materials.[28][29] For extraction and cleaning purposes, dimethoxymethane is employed in pharmaceutical processes as a valuable extraction solvent for purifying active compounds and protein-based drugs, owing to its polarity and volatility that support chromatography and separation techniques. It also finds use in cleaning applications, such as removing grease and contaminants from electronic components and machinery, as well as in paint strippers for varnish and coating removal due to its strong solvency and rapid evaporation. Classified as a green solvent, it offers a safer alternative in these roles, minimizing environmental and health risks associated with more hazardous options.[29][30][31] In the perfumery and flavors industry, dimethoxymethane acts as a diluent and carrier for essential oils and fragrances in cosmetic formulations, benefiting from its mild odor and broad solvency that preserve scent integrity without interference. It enhances spray performance in products like aerosols, hair sprays, nail polish removers, and sun protection items, supporting the sector's demand for efficient, low-residue solvents.[32][29]Reagent in organic synthesis
Dimethoxymethane serves as a versatile reagent in organic synthesis, particularly for protecting functional groups and generating reactive formaldehyde equivalents under acid catalysis. In carbonyl protection, it participates in transacetalization reactions with aldehydes and ketones to form dimethyl acetals, as illustrated by the general equation:
This process is reversible upon treatment with mild acid, allowing for selective deprotection, and the volatile formaldehyde byproduct facilitates easy removal under reduced pressure.[33] The reaction is typically catalyzed by Brønsted or Lewis acids and is advantageous in scenarios where excess alcohol solvents are undesirable, providing a clean method for stabilizing carbonyls during multi-step syntheses.[34]
As a formylating agent, dimethoxymethane acts as an electrophilic formaldehyde equivalent, enabling the introduction of formyl or hydroxymethyl groups in various transformations. Under acidic conditions, it generates reactive species suitable for reactions analogous to Vilsmeier-Haack formylation variants, where it supplies the formaldehyde unit for electrophilic aromatic substitution or other carbon-carbon bond formations.[35] For instance, in the synthesis of pillararenes or related macrocycles, dimethoxymethane has been employed as a nonaqueous, safe alternative to gaseous formaldehyde, promoting condensation reactions with high efficiency and minimal side products.[35]
In peptide synthesis, dimethoxymethane is utilized to install methoxymethyl (MOM) protecting groups on hydroxyl functionalities of amino acid side chains, such as those in serine and threonine residues. The protection proceeds via acid-catalyzed reaction of the alcohol with dimethoxymethane, yielding the MOM ether (ROCH₂OCH₃) and methanol as byproduct:
This method, often employing catalysts like ZrCl₄ or P₂O₅, offers high yields at room temperature under solvent-free conditions and is compatible with solid-phase peptide synthesis protocols.[36] The MOM group is stable to basic conditions and organometallics but readily removed with mild acid, making it ideal for orthogonal protection strategies in complex peptide assemblies.[34]
Dimethoxymethane also finds application in the O-methylation of phenols, serving as a mild methylating source under Lewis acid catalysis to afford methyl phenyl ethers, though this is less common than standard alkylating agents. Its role in carbohydrate chemistry is particularly notable, where it facilitates transacetalization for forming 4,6-O-methylene acetals in pyranosides of glucose, galactose, mannose, and fructose, enhancing selectivity in protecting vicinal diols.[37] Additionally, in glycoside manipulations, dimethoxymethane promotes ether exchange and isomerization of glycosidic bonds, aiding in the synthesis of methyl levulinates from sugars like xylose.[38] The volatile formaldehyde byproduct in these transacetalizations simplifies purification, underscoring dimethoxymethane's utility as a clean, efficient reagent in synthetic carbohydrate transformations.[37]