Dimethyl ether
Dimethyl ether (DME), chemically denoted as CH₃OCH₃, is the simplest ether, consisting of two methyl groups linked by an oxygen atom, and exists as a colorless, low-boiling gas at standard temperature and pressure.[1] With a molecular weight of 46.07 g/mol and a boiling point of -24.8 °C, it can be readily liquefied under moderate pressure for storage and transport, exhibiting properties akin to liquefied petroleum gas (LPG).[2] Flammable yet low in toxicity, DME features a faint ethereal odor and high vapor pressure, rendering it suitable for applications requiring rapid evaporation.[3] The compound's primary industrial use centers on its role as an aerosol propellant in products like hairsprays, foams, and insecticides, prized for its non-ozone-depleting nature and miscibility with water and solvents.[1] Additionally, it serves as a refrigerant (under designation R-E170), extracting agent, and chemical intermediate for synthesizing compounds such as dimethyl sulfate and acetic acid.[1] Its production, chiefly via catalytic dehydration of methanol sourced from syngas or biomass, positions DME as a versatile intermediate in chemical manufacturing.[4] Emerging applications highlight DME's potential as a diesel substitute in compression-ignition engines, where its high cetane number (around 55) and oxygen content enable low-NOx and soot-free combustion, potentially reducing particulate emissions compared to conventional fuels.[5] Research underscores its viability for blending with diesel or use in dedicated engines, supported by infrastructure similarities to LPG, though challenges include lower energy density requiring larger storage volumes.[6] Safety considerations emphasize its extreme flammability, with an NFPA health rating of 2 due to asphyxiation risks in confined spaces, necessitating careful handling akin to other compressed gases.[7]Properties
Physical Properties
Dimethyl ether has the molecular formula C₂H₆O (or CH₃OCH₃) and a molar mass of 46.068 g/mol.[8] It exists as a colorless gas under standard temperature and pressure conditions, exhibiting a faint ethereal odor.[1] The compound's melting point is -141.5 °C, and its normal boiling point is -24.8 °C, allowing it to liquefy readily under moderate pressure at ambient temperatures.[9] [1] Key physical parameters include a liquid density of approximately 0.66 g/cm³ at its boiling point and a vapor pressure of 5.2 bar at 20 °C, contributing to its high volatility.[10] [11] The vapor density relative to air is 1.6, indicating it is heavier than air and may accumulate in low-lying areas.[9] Solubility in water is limited at 71 g/L (or 7.1 g/100 mL) at 20 °C, though it mixes well with organic solvents.[1] Thermodynamic properties relevant to phase behavior include a critical temperature of 126.9 °C and a critical pressure of 53.7 bar.[10] These values define the conditions beyond which dimethyl ether cannot be liquefied by pressure alone, influencing its handling in pressurized systems.[12]| Property | Value | Conditions |
|---|---|---|
| Molar mass | 46.068 g/mol | - |
| Melting point | -141.5 °C | 1 atm |
| Boiling point | -24.8 °C | 1 atm |
| Liquid density | 0.66 g/cm³ | At boiling point |
| Vapor pressure | 5.2 bar | 20 °C |
| Critical temperature | 126.9 °C | - |
| Critical pressure | 53.7 bar | - |
| Water solubility | 71 g/L | 20 °C |