Dimethyl Carbonate

C₃H₆O₃ organic

Molar Mass

90.078 g/mol

Properties

State	Liquid (colorless with pleasant odor)
Color	Colorless
Solubility	Slightly soluble in water (139 g/L at 20°C); miscible with most organic solvents
Melting Point	4.6°C
Boiling Point	90°C

About Dimethyl Carbonate

Dimethyl carbonate is the green-chemistry replacement reagent that actually delivered. Historically, methylations used dimethyl sulfate (Schedule 2 chemical weapons precursor, lethal at low inhalation doses) or methyl iodide (CMR, ozone-active), and carbonylations used phosgene (the World War I poison). DMC steps in at both jobs because it has dual reactivity: under basic conditions a nucleophile attacks the methyl carbon and you do an SN2-style methylation with methyl carbonate as the leaving group, releasing CO2 and methanol after protonation; under acidic conditions or at high temperature the same nucleophile attacks the carbonyl carbon and you transfer the -C(O)OMe group, doing a carbonylation/transesterification. Tundo's group at Venice worked out the selectivity rules in the 1990s and the chemistry has been adopted in pharma, agrochemicals, and polycarbonate manufacturing. DMC itself is made cleanly: oxidative carbonylation of methanol with CO and O2 over a Cu chloride catalyst, or via methanol + propylene oxide → propylene carbonate → transesterification. No phosgene anywhere. The other major use is as a co-solvent in lithium-ion battery electrolytes, where DMC pairs with ethylene carbonate (EC) — EC has the high dielectric constant needed to dissolve LiPF6 to molar concentrations, DMC has the low viscosity needed for high lithium-ion conductivity, and the EC/DMC mixture in roughly 1:1 ratio is the textbook electrolyte solvent in LFP and NMC cells. With global EV cell production, that is a multi-hundred-thousand-tonne-per-year market for DMC alone.

Where you'll encounter it

If you have opened up a lithium-ion 18650 cell or a pouch cell from a Tesla teardown, the wet electrolyte you smell is mostly EC/DMC with 1 M LiPF6. In a process-development lab, DMC shows up when somebody asks 'how do we methylate this without using methyl iodide' — heat the substrate with DMC and a base like K2CO3 or DBU at 90-160 °C and you methylate phenols, NH-azoles, and stabilized C-H acids cleanly with methanol and CO2 as the only byproducts.

Common Uses

Green-chemistry methylating agent replacing dimethyl sulfate and methyl iodide for phenol O-methylation
Carbonylating reagent replacing phosgene in isocyanate, polycarbonate, and carbamate synthesis
Co-solvent with ethylene carbonate in LiPF6 lithium-ion battery electrolytes (EC/DMC 1:1 baseline)
Fuel oxygenate additive blended into gasoline in EU markets to raise oxygen content and reduce CO emissions
Methyl-ester solvent for cleaning, degreasing, and resin formulation in lower-VOC paint systems
Reaction solvent and methyl source in melt polycarbonate production (Asahi non-phosgene process)
Building block for dimethyl ureas, methyl carbamates, and mixed alkyl carbonate intermediates
Phase-transfer-catalyzed N-methylation of indoles, imidazoles, and amines in fine-chemical synthesis

Safety Information

Flammable liquid — flash point 18 °C (closed cup), autoignition 458 °C, explosion limits 4.2-12.9 vol%. GHS: H226 (flammable liquid and vapor), H319 (causes serious eye irritation), H336 (may cause drowsiness or dizziness). No OSHA PEL has been set. ACGIH has not assigned a TLV; industrial workplaces typically operate under a 25-50 ppm internal limit. Acute oral LD50 in rats is 13,000 mg/kg — orders of magnitude lower toxicity than dimethyl sulfate (LD50 ~440 mg/kg) or methyl iodide (LD50 ~76 mg/kg). Biodegradable, low aquatic toxicity, no ozone-depletion potential. The remaining handling concern is fire risk: keep away from ignition sources, store in cool ventilated cabinets, ground containers when transferring bulk, and treat the vapor in confined spaces seriously.

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.

Constituent Elements

C — Carbon H — Hydrogen O — Oxygen

Frequently Asked Questions

What is the molar mass of dimethyl carbonate?

90.078 g/mol — three carbons (3 × 12.011), six hydrogens (6 × 1.008), three oxygens (3 × 15.999). Density 1.069 g/mL, so 100 mL is about 107 g or 1.19 mol. Useful when you are sizing a methylation reaction where DMC is used in 2-5 equiv excess as both reagent and solvent.

Why is dimethyl carbonate considered a green reagent?

It directly replaces three of the most hazardous reagents in classical synthesis. In place of dimethyl sulfate (chemical weapon precursor, fatal at gram-scale skin exposure) for methylation. In place of methyl iodide (carcinogenic, ozone-depleting) for the same job. In place of phosgene (acutely lethal, World War I poison) for carbonylation. DMC byproducts are CO2 and methanol — both harmless on the relevant scales. DMC itself is biodegradable, has low ecotoxicity, and is made without phosgene in the first place. Roger Sheldon-style E-factor calculations consistently favor DMC routes.

How is DMC used in batteries?

It is one half of the most common lithium-ion electrolyte solvent system: ethylene carbonate plus DMC, typically 1:1 by volume, with 1.0-1.2 M LiPF6 dissolved in it. EC contributes high dielectric constant (~90) to ionize the salt and forms the SEI layer on the graphite anode. DMC contributes low viscosity (~0.59 cP) for high ionic conductivity and lowers the freezing point so the cell works in cold weather. Newer formulations swap part of the DMC for EMC or DEC to push low-temperature performance further, but EC/DMC remains the baseline you compare everything against.