Methyl formate
Methyl formate, also known as methyl methanoate, is the simplest carboxylate ester, formed from formic acid and methanol, with the chemical formula HCOOCH₃ or C₂H₄O₂ and a molecular weight of 60.05 g/mol.[1][2] It appears as a clear, colorless liquid with a pleasant, ethereal or fruity odor, exhibiting high volatility due to its low boiling point of approximately 32 °C (90 °F) and melting point of -99.8 °C (-147.6 °F).[1][3] This compound is soluble in water (30 g/100 mL at 20 °C), miscible with ethanol and ether, and has a density of about 0.977 g/cm³ at 20 °C, making it slightly less dense than water.[1][2][4] In terms of chemical properties, methyl formate is highly flammable with a flash point of -27 °F (-33 °C) and explosive limits between 5% and 23% in air, and it reacts slowly with water to hydrolyze into formic acid and methanol.[1][5] Its structure features a formyl group (–CHO) attached to a methoxy group (–OCH₃), rendering it a key intermediate in organic synthesis.[1] Industrially, it is primarily produced via the base-catalyzed carbonylation of methanol with carbon monoxide, though it can also be synthesized by the acid-catalyzed esterification of formic acid and methanol or through reactions involving sodium formate and hydrochloric acid.[3][1] Methyl formate finds wide application as a solvent in quick-drying finishes, a blowing agent for polyurethane foams and polystyrene, and an intermediate in the production of chemicals such as formamide, dimethylformamide, formic acid, and dimethyl carbonate.[1][2] It is also employed as an agricultural fumigant, larvicide, and insecticide, and historically served as a refrigerant alternative to sulfur dioxide.[3][1] Additionally, it occurs naturally in sources like apples, coffee, and cigarette smoke, and has been studied as a model compound for biodiesel combustion kinetics.[1][3] From a safety perspective, methyl formate poses significant hazards due to its flammability and potential for ignition from sparks or hot surfaces, with an autoignition temperature of 455 °C (851 °F).[5] Exposure can irritate the eyes, skin, and respiratory system; inhalation may cause mucous membrane irritation, narcosis, visual disturbances, or respiratory distress at high concentrations, while ingestion leads to gastrointestinal irritation and central nervous system depression.[5][2] The occupational exposure limit is set at 50 ppm as a time-weighted average, with an immediately dangerous to life or health concentration of 4500 ppm.[1]Properties
Physical properties
Methyl formate, with the chemical formula HCOOCH₃, is the simplest formate ester and has a molar mass of 60.052 g/mol.[1] It appears as a clear, colorless liquid with a pleasant, ethereal odor.[2] The compound exhibits the following key physical properties:| Property | Value | Conditions |
|---|---|---|
| Density | 0.974 g/cm³ | 20 °C |
| Melting point | −99.8 °C (−147.6 °F) | - |
| Boiling point | 31.9–32.0 °C (89.4–89.6 °F) | 760 mmHg |
| Vapor pressure | 634 hPa | 20 °C |
| Refractive index | 1.343 | 20 °C |
| Flash point | −32 °C (closed cup) | - |
Chemical properties
Methyl formate possesses the structural formula H−C(=O)−O−CH₃, characterized by a planar carbonyl group and a C-O-C ester linkage typical of formate esters.[1][6] Its systematic IUPAC name is methyl methanoate, while the common name is methyl formate; it is classified as the methyl ester of formic acid.[6][1] In infrared (IR) spectroscopy, the characteristic carbonyl (C=O) stretching vibration occurs at approximately 1745 cm⁻¹, reflecting the conjugated ester functionality.[7] The ¹H nuclear magnetic resonance (NMR) spectrum displays a singlet for the formyl hydrogen at around 8.0 ppm and a singlet for the methoxy methyl group at approximately 3.7 ppm, indicative of the distinct electronic environments in the molecule. Methyl formate exhibits thermal stability up to its boiling point but undergoes decomposition above 400°C, primarily yielding methanol, formaldehyde, and carbon monoxide via unimolecular pathways. As an ester, it is sensitive to strong bases and acids, which can catalyze hydrolysis or transesterification, though it reacts slowly with water alone to form formic acid and methanol.[5] The molecule is polar, with an experimental dipole moment of 1.77 D, arising from the electronegative oxygen atoms in the ester group; this polarity contributes to its classification as a polar aprotic solvent and moderate solubility in water.[8][1]Production
Laboratory synthesis
Methyl formate is commonly synthesized in the laboratory through the acid-catalyzed esterification of formic acid with methanol. The reaction proceeds as an equilibrium process: \ce{HCO2H + CH3OH ⇌ HCO2CH3 + H2O} A strong acid catalyst, such as concentrated sulfuric acid (typically 1–5 mol%), is employed to protonate the carbonyl oxygen of formic acid, facilitating nucleophilic attack by methanol. To shift the equilibrium toward the ester, an excess of methanol is used, often in a 1:1.5 molar ratio of formic acid to alcohol. The mixture is refluxed at 60–70°C for 2–4 hours, after which the reaction yields approximately 80% methyl formate based on the limiting reactant. An alternative laboratory route involves the nucleophilic substitution reaction of methyl iodide with silver formate, leveraging the good leaving group ability of iodide and the reactivity of the silver carboxylate: \ce{CH3I + HCOOAg -> HCO2CH3 + AgI} This method is particularly suitable for small-scale preparations and occurs at room temperature in an inert solvent like diethyl ether, providing high yields (often >90%) due to the SN2 mechanism favored by the primary alkyl halide. The silver iodide precipitate can be easily filtered, simplifying product isolation.[9] Following synthesis by either method, methyl formate is purified by distillation under reduced pressure to accommodate its low boiling point of 32°C, allowing collection at ambient temperatures (e.g., 20–25°C at 100–200 mmHg) and minimizing volatilization losses. This volatility, a key physical property, ensures efficient separation from water and unreacted reagents. Yields in laboratory settings typically reach 70–85% after purification, depending on the scale and equilibrium management.Industrial production
The industrial production of methyl formate predominantly relies on the catalytic carbonylation of methanol with carbon monoxide, represented by the reaction CH₃OH + CO → HCOOCH₃. This liquid-phase process, commercialized by BASF since the early 20th century, employs homogeneous alkali methoxide catalysts such as sodium methoxide (typically 1-5 wt%) in excess methanol as the solvent. The reaction proceeds at moderate temperatures of 80–160 °C and pressures of 20–50 bar, yielding high selectivity to methyl formate, often exceeding 95%, with dimethyl ether as a minor byproduct from side reactions.[10][11][12] An alternative industrial route, though less prevalent due to the elevated cost of formic acid feedstock, involves the direct esterification of formic acid with methanol: HCOOH + CH₃OH → HCOOCH₃ + H₂O. This equilibrium-limited reaction is catalyzed by acidic ion-exchange resins, such as sulfonic acid-functionalized polystyrene types (e.g., Amberlyst series), operating at 60–100 °C under atmospheric or slightly elevated pressure, with water removal via distillation to drive conversion toward 90–95% yield. The method's economic disadvantage stems from formic acid pricing, which is roughly 2–3 times that of methanol on a per-unit basis.[10][13][14] Global production capacity for methyl formate reached approximately 6.8 million metric tons per year in 2024, driven by demand in Asia-Pacific regions for downstream chemical intermediates. Key producers include BASF SE (Germany), Eastman Chemical Company (USA), and Mitsubishi Gas Chemical Company (Japan), with facilities optimized for integrated carbonylation operations to minimize logistics costs. The carbonylation route dominates, accounting for over 90% of output, owing to its atom-efficient design and low byproduct formation—primarily unreacted gases that are recycled—resulting in near-stoichiometric material utilization and reduced environmental footprint compared to esterification.[15][16][17]Chemical reactions
Hydrolysis and ester exchange
Methyl formate undergoes acid-catalyzed hydrolysis to produce formic acid and methanol, according to the reaction HCOOCH₃ + H₂O ⇌ HCOOH + CH₃OH. This process is equilibrium-limited, with an equilibrium constant of approximately 0.14 at a water-to-ester molar ratio of 1 and temperatures around 80–110 °C, and it is endothermic with ΔH°_R = +16.3 kJ/mol.[18] Common catalysts include sulfuric acid, hydrochloric acid, or the formic acid produced in situ, and the reaction rate increases with temperature, typically conducted at 100–140 °C in industrial settings to regenerate formic acid from methyl formate.[19] The kinetics follow a second-order rate law, rate = k [HCOOCH₃][H⁺], but under excess water conditions, it approximates pseudo-first-order behavior with respect to the ester. In contrast, base hydrolysis (saponification) of methyl formate proceeds more rapidly than the acid-catalyzed variant, yielding sodium formate and methanol via HCOOCH₃ + NaOH → HCOONa + CH₃OH.[20] This reaction is quantitative under alkaline conditions due to the irreversible formation of the carboxylate salt, with mechanistic studies indicating nucleophilic attack by hydroxide ion as the rate-determining step.[20] A base-catalyzed second-order rate constant of 16 L/mol·s has been estimated for environmental conditions, though industrial applications favor acid catalysis for formic acid recovery.[21] Transesterification of methyl formate with alcohols such as ethanol yields the corresponding formate ester and methanol, as in HCOOCH₃ + ROH ⇌ HCOOR + CH₃OH, often used to produce ethyl formate.[22] The reaction is catalyzed by acids or bases and is equilibrium-driven with a constant near 1 for similar alkyl groups, allowing reversible exchange under mild conditions.[22] Overall, the hydrolysis kinetics in acidic media exhibit pseudo-first-order dependence on water, highlighting the reaction's sensitivity to catalytic and thermal conditions.Other reactions
Methyl formate can undergo reduction using strong reducing agents such as lithium aluminum hydride (LiAlH₄), which typically converts it to two equivalents of methanol through full reduction of the ester functionality.[23] However, selective reduction targeting the formyl group can yield methanol and formaldehyde, as demonstrated in hydride transfer reactions with metal complexes like bis(diphosphine) rhodium or platinum hydrides, where the ester is cleaved to produce formaldehyde and methoxide (which protonates to methanol) under mild conditions in solvents like acetonitrile or tetrahydrofuran. Catalytic hydrogenation over copper-based catalysts also reduces methyl formate primarily to methanol, though conditions can be tuned for partial selectivity toward formaldehyde in specialized systems.[24] Thermal decomposition of methyl formate occurs in the vapor phase at 200–500 °C (preferably 250–400 °C), primarily yielding carbon monoxide and methanol.[25] This process can be catalyzed by metals like palladium on activated carbon to enhance selectivity and rate, producing high-purity CO and methanol mixtures suitable for syngas-like applications in fuel synthesis.[26] At higher temperatures or under specific catalytic conditions, decomposition may generate syngas mixtures (CO + H₂) through secondary reactions involving methanol.[27] Methyl formate reacts with amines to form N-formamides, with methanol as a byproduct, serving as a mild formylation agent in organic synthesis.[28] For example, the reaction with ammonia produces formamide (HCONH₂) and methanol, often catalyzed by bicyclic guanidines at room temperature, providing an efficient route to intermediates like N,N-dimethylformamide (DMF) via subsequent methylation.[29] This transformation proceeds through nucleophilic attack of the amine on the carbonyl carbon, displacing the methoxy group. Photochemical reactions of methyl formate under ultraviolet irradiation generate methoxy, methyl, and formyl radicals through C-O bond cleavage, enabling radical-mediated transformations.[30] These processes are limited in scope but relevant for gas-phase studies, where radical recombination or further reactions can lead to products like methanol and carbon monoxide.[30]Uses
Industrial applications
Methyl formate serves as a key intermediate in various industrial processes, with global production volumes reaching approximately 842,000 tonnes in 2024, primarily directed toward chemical manufacturing and materials production.[31] Its versatility stems from its reactivity and favorable environmental profile, enabling large-scale applications in sectors such as chemicals, foams, and refrigeration. A major industrial use of methyl formate is as a precursor to formic acid through hydrolysis, accounting for about 59% of global formic acid production in 2024.[32] This process involves the catalytic hydrolysis of methyl formate in the presence of sulfuric acid or other catalysts, yielding formic acid and methanol, which supports applications in leather tanning, textiles, and agriculture on a scale of over 600,000 tonnes of formic acid annually from this route. Methyl formate is also widely employed in the synthesis of formamides, particularly dimethylformamide (DMF), a critical solvent in pharmaceuticals and polymers. The reaction proceeds via carbonylation, where methyl formate reacts with dimethylamine to produce DMF and methanol:\ce{HCOOCH3 + HN(CH3)2 -> HCON(CH3)2 + CH3OH}
This method is favored industrially for its efficiency and use of readily available feedstocks, contributing significantly to the annual production of hundreds of thousands of tonnes of DMF.[33] In the production of polyurethane foams, methyl formate acts as an environmentally friendly blowing agent, replacing chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) due to its zero ozone depletion potential. It facilitates foam expansion at temperatures of 30–50°C, driven by its boiling point of approximately 32°C, and is used in rigid foams for insulation in appliances and construction, offering low thermal conductivity and rapid environmental degradation.[34] Additionally, methyl formate is utilized as a refrigerant under the designation R-611 in low-temperature systems, such as certain industrial chillers and cascade refrigeration setups. Its global warming potential (GWP) is low at 13 over a 100-year horizon, making it a sustainable alternative to high-GWP hydrofluorocarbons in niche applications where its flammability can be managed.[35]