Dimethyl Ether
Properties
| State | Gas (colorless with mild sweet ethereal odor; liquid under pressure) |
| Color | Colorless |
| Solubility | Moderately soluble in water (71 g/L at 20°C); miscible with most organic solvents |
| Melting Point | -141°C |
| Boiling Point | -24°C |
About Dimethyl Ether
Dimethyl ether is the textbook proof that hydrogen bonding is what controls boiling point. DME and ethanol are constitutional isomers — same C2H6O molecular formula, same 46.07 g/mol, same 16 valence electrons. Ethanol boils at 78 °C and is fully miscible with water. DME boils at -24 °C, is a gas at room temperature, and only dissolves to about 71 g/L. The single difference is that ethanol has an O-H bond and can donate hydrogen bonds; DME has neither hydroxyl proton nor donor capacity, so it can only accept hydrogen bonds, and the cohesion in pure DME drops to dipole-dipole and dispersion forces. Industrially, DME is produced by methanol dehydration over an acid catalyst (γ-Al2O3 or H-ZSM-5) in a fixed bed, and increasingly via direct synthesis from syngas (CO + H2) over bifunctional Cu/ZnO/Al2O3 catalysts. The compound has three significant commercial roles. First, aerosol propellant — it replaced CFCs in hairspray, deodorant, and air freshener cans because it has zero ODP, low GWP (~1 over 100 years), and dissolves into product formulations. Second, alternative diesel fuel: DME has a cetane number around 55-60 (versus 40-55 for petroleum diesel), no C-C bonds so combustion produces no soot, and high oxygen content for clean burn. Volvo and several Chinese manufacturers have run trial fleets. Third, refrigerant R-E170 in low-temperature systems where flammability is acceptable. The downside is the same as the upside: low boiling point means you have to handle it as a liquefied gas under pressure, and the LFL/UFL window of 3.4-27% in air is wide.
Where you'll encounter it
If you have ever shaken a propellant-driven aerosol can and felt the slosh of a liquid inside, that liquid is mostly DME (or a propane/butane blend in older formulations). DME also turns up as the fuel feed in diesel-fleet pilot programs in Sweden, Japan, and China — one of those technologies that keeps almost-arriving without quite displacing diesel at scale because the infrastructure costs of propane-style pressurized fuel handling are real. In a formulation lab dialing in a hairspray, DME at 30–60% by weight serves both as propellant and as a co-solvent that lets the polymer film redissolve when sprayed. In a methanol-dehydration pilot reactor, a fixed bed of γ-Al2O3 at 250–350 °C converts methanol to DME plus water with near-quantitative selectivity. And in an undergraduate organic class, the ethanol/DME pair is the textbook one-line proof that hydrogen bonding raises boiling point by a hundred degrees.
Common Uses
- Aerosol propellant in hairspray, deodorants, and air fresheners after the CFC phaseout under the Montreal Protocol
- Alternative diesel fuel with cetane number 55-60 and zero soot in compression-ignition engine trials
- Refrigerant designation R-E170 in low-temperature commercial and pilot residential systems
- Blowing agent for rigid polyurethane and polystyrene foam panels replacing HCFCs and HFCs
- Hydrogen carrier and clean cooking fuel in LPG-blended formulations sold in China and Korea
- Methylating agent in supercritical-fluid organic synthesis at 50-150 bar for selective O-methylation
- Solvent for lithium-aluminum-hydride reductions at low temperatures where Et2O would freeze out
- Educational demonstration compound for constitutional isomerism with ethanol in undergraduate chemistry
Safety Information
Extremely flammable gas — autoignition 235 °C, flammability range 3.4-27 vol% in air, vapor density 1.6 (heavier than air, so leaks pool in low spots and travel along benches). GHS: H220 (extremely flammable gas), H280 (gas under pressure — refrigerated/liquefied container hazards), H336 (drowsiness/dizziness). No OSHA PEL or ACGIH TLV has been established; internal industrial limits are typically 1000 ppm 8-hour. Acute toxicity is low — the LC50 in rats is 308,000 ppm over 4 hours, essentially asphyxiation. The two real hazards are fire/explosion (treat handling like LPG, with bonded and grounded transfer, no ignition sources, leak detectors in confined spaces) and simple oxygen displacement in poorly ventilated areas. DME does not form peroxides on storage, which is one advantage over diethyl ether.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.