Dimethyl carbonate (DMC, CAS 616-38-6) occupies an unusual position among industrial solvents: it is at once a commodity oxygenate made in hundred-thousand-tonne trains, a specification-critical electrolyte component where the difference between 20 and 200 ppm of water decides whether a battery cell passes formation, and a green-chemistry reagent that has replaced phosgene and dimethyl sulfate in a growing list of processes. The molecule is the same in all three roles. Only the impurity envelope changes.
This article covers the chemistry, the four manufacturing routes that matter industrially, the logic that connects the three commercial grades to their applications, and the handling realities – including the fact that DMC is a flammable liquid with a flash point near 17 degC, which surprises formulators who read “low toxicity, readily biodegradable” and assume “not dangerous goods”.
The product is catalogued, with the full three-grade specification, on our Dimethyl Carbonate (DMC) 99.95% product page.
1. The molecule
| Property | Value | Why it matters |
|---|---|---|
| Formula / MW | C3H6O3 / 90.08 | smallest organic carbonate |
| Oxygen content | 53.29% by mass | the basis of its use as a fuel oxygenate |
| Boiling point | 90 degC | easy to strip, easy to lose to the vent |
| Melting point | about 2 to 4 degC | winter handling and pump lines |
| Flash point | about 17 degC, closed cup | flammable liquid, class 3, UN 1161 |
| Density | 1.069 g/cm3 at 20 degC | heavier than water; phase behaviour in work-ups |
| Viscosity | about 0.59 mPa s at 25 degC | the reason it is in electrolyte blends at all |
| Dielectric constant | about 3.1 | low on its own; paired with ethylene carbonate in cells |
| Water solubility | mutual, limited (of the order of 14 g per 100 mL at 20 degC) | drying below 100 ppm needs a train, not a single distillation |
| InChIKey | IEJIGPNLZYLLBP-UHFFFAOYSA-N | identity |
| PubChem CID | 12021 | identity |
Two of these numbers explain most of the product’s commercial behaviour. The 53.29% oxygen figure is why DMC is valuable as an oxygenate and why its blending economics are so different from a hydrocarbon solvent: a relatively small volume carries a large amount of oxygen into a fuel or a formulation. The 17 degC flash point is why DMC cannot be treated as a benign alternative to ketones in an open plant – it flashes below ambient summer temperatures.
2. Four manufacturing routes
2.1 Oxidative carbonylation of methanol
2 CH3OH + CO + 1/2 O2 -> (CH3O)2CO + H2O
Methanol, carbon monoxide and oxygen over a copper chloride catalyst – the route commercialised first and still run in several plants. It is atom-economical on paper and awkward in practice: the water co-produced hydrolyses both the product and, more importantly, deactivates the catalyst, so the reaction is run with water removal and the reactor materials must survive chloride. Selectivity to DMC versus the competing dimethyl oxalate and methyl formate pathways is a function of catalyst promotion and of the CO/O2 ratio.
2.2 Transesterification of cyclic carbonates
Ethylene carbonate + 2 CH3OH -> DMC + ethylene glycol
The dominant route in China. Ethylene carbonate (made from ethylene oxide and carbon dioxide) or propylene carbonate is transesterified with methanol, and the co-product is a glycol – ethylene glycol or propylene glycol – that is itself a saleable commodity. The route’s attractions are that it consumes CO2 in the cyclic carbonate step, avoids phosgene and CO entirely, and produces two products with established markets. Its constraint is the azeotrope: DMC and methanol form a minimum-boiling mixture, so the separation of methanol from DMC requires extractive or pressure-swing distillation, and that separation is where most of the energy and most of the capital sit.
Our propylene carbonate listing is the other half of that pair for buyers who need both ends of the chemistry.
2.3 Urea alcoholysis
CO(NH2)2 + 2 CH3OH -> (CH3O)2CO + 2 NH3
Urea plus methanol, with the ammonia recycled. Attractive where urea is cheap and ammonia has a use on site; the drawback is that the thermodynamics need ammonia removal to drive conversion, and the reactor duty is high. Several Chinese plants run this route, often in combination with melamine or fertiliser operations.
2.4 Direct synthesis from CO2 and methanol
2 CH3OH + CO2 -> (CH3O)2CO + H2O
The most studied and least commercial of the four, because the equilibrium lies well to the left and the water produced must be removed continuously to shift it. Routes around the problem use dehydrating agents, acetals, or a membrane reactor. The chemistry is the green-chemistry flagship; the economics still depend on cheap CO2, cheap hydrogen-derived methanol and a way to handle the water.
Which route made your drum matters commercially even though the molecule is identical: transesterification product carries traces of glycol and of the cyclic carbonate, oxidation product carries traces of methyl formate, dimethyl oxalate and chloride-derived species, and urea route product carries traces of ammonia and methyl carbamate. These are the impurities a good certificate should name.
3. The three grades and what separates them
| Parameter | Battery | High purity | Technical |
|---|---|---|---|
| Purity (GC) | 99.95% min | 99.90% min | 99.50% min |
| Carbonate content | 99.99% min | 99.97% min | 99.95% min |
| Methanol | 100 ppm max | 200 ppm max | 500 ppm max |
| Water (KF) | 20 ppm max | 100 ppm max | 200 ppm max |
| Colour (APHA) | 5 max | on request | on request |
The grade ladder is not a marketing device; each step corresponds to a real engineering stage.
- From technical to high purity is mostly a distillation and drying problem: the GC number tightens from 99.5 to 99.9 and the water from 200 to 100 ppm.
- From high purity to battery adds two things that cannot be recovered downstream: water at 20 ppm requires the drying train to be working perfectly, and colour at 5 APHA requires that the product never met a hot surface, a rusty line or a dissolved-oxygen-rich headspace during transfer.
- Carbonate content is measured titrimetrically and is a check on the functionality rather than on the volatiles: a lot can be 99.5% by GC and 99.95% as carbonate when the balance is methanol and water.
See Battery-Grade Dimethyl Carbonate for why the 20 ppm water and 100 ppm methanol limits are set where they are, including the LiPF6 hydrolysis arithmetic that produces them.
4. Application map
| Application | Grade | Function | Key driver |
|---|---|---|---|
| Li-ion electrolyte co-solvent | battery | lowers viscosity, widens the liquid range | water and methanol limits |
| Polycarbonate, non-phosgene | high purity | DMC to diphenyl carbonate to PC | methanol carry-over |
| Methylating agent | technical or high purity | O-, N-, S- and C-methylation | cost per methyl, waste profile |
| Coatings and cleaning solvent | technical | medium-polarity solvent, good solubility for PU, acrylic and epoxy | flash point and drying rate |
| Fuel oxygenate | technical | 53% oxygen by mass | blending economics |
| Pharmaceutical and agrochemical processing | high purity | solvent and methoxycarbonylating reagent | residual solvent compliance |
4.1 Electrolyte solvent
DMC is blended with ethylene carbonate and with linear carbonates such as ethyl methyl carbonate and diethyl carbonate. Ethylene carbonate supplies the high dielectric constant needed to dissociate the lithium salt but is viscous and melts near 36 degC; DMC supplies low viscosity, a melting point near 2 degC and electrochemical stability on the cathode. Typical solvent packages use DMC as the low-viscosity component at a third to a half of the blend. The specification-critical impurities are water (hydrolyses the salt) and methanol (reacts with lithium and with the salt).
4.2 Polycarbonate without phosgene
DMC reacts with phenol to give diphenyl carbonate, which is melt-transesterified with bisphenol A. The route replaces phosgene entirely, which is why it has displaced older technology in new capacity. It is covered in detail in Dimethyl Carbonate in Non-Phosgene Polycarbonate.
4.3 Methylation
DMC methylates phenols, amines, thiols and active methylene compounds; under harder conditions it transfers the entire methoxycarbonyl group. Its advantages over dimethyl sulfate and methyl iodide are toxicity and waste: the leaving group is methanol and the by-product is carbon dioxide, not sulfate or iodide brine. Its disadvantage is that the chemistry needs higher temperature, pressure or a catalyst. The comparison is set out in DMC as a Methylating Agent, and the classical alternative is described in Dimethyl Sulfate as a Methylating Agent.
4.4 Solvent, oxygenate and the rest
As a solvent DMC sits in the medium-polarity, medium-boiling band: high enough to dissolve polyurethane and epoxy components, low enough to strip at the end of a batch. As an oxygenate its 53.29% oxygen content makes it a compact way to raise the oxygen level of a fuel blend. Its cousin glycerol carbonate shares the carbonate functionality and appears in overlapping applications.
5. Hazards, handling and transport
DMC is a flammable liquid: flash point about 17 degC closed cup, class 3, UN 1161, packing group II. In practice that means bonded and earthed transfer, no plastic drums for flammable service without the appropriate certification, vapour-tight pumps, and area classification for a solvent that flashes below summer ambient.
Chemically, the handling issues are hydrolysis and, in the presence of base, transesterification. DMC hydrolyses slowly to methanol and carbon dioxide; the reaction accelerates with temperature and pH, which means that a wet drum which also picks up alkaline contamination degrades in two directions at once. Because the two main impurities are linked to the same reaction, a moisture excursion shows up as rising water and rising methanol together, which makes the pair a useful diagnostic.
Store cool, dry and well ventilated, containers closed, away from ignition sources and oxidisers. Battery grade is supplied under dry nitrogen in internally coated steel drums and ISO tanks; high-purity and technical grades in 200 L drums and 1000 L IBCs.
6. Purchasing guide
- State the grade and the analytical values, not the grade name alone: two suppliers’ “battery grade” can differ by a factor of five on water.
- Ask which manufacturing route the plant runs, because it predicts the impurity set.
- For electrolyte use, require water and methanol by lot, and agree the sampling method – a wet sampler invalidates a 20 ppm specification.
- For polycarbonate use, ask for the methanol figure and for the glycol or cyclic carbonate carry-over, which are the transesterification route’s fingerprints.
- Confirm the transport classification and packaging before the first shipment; DMC is dangerous goods and that affects both freight cost and lead time.
7. Frequently asked questions
Why does battery grade need 20 ppm water when the technical grade allows 200?
Because the electrolyte salt hydrolyses. One mole of water destroys one mole of LiPF6 and releases two moles of hydrogen fluoride; in a kilogram of electrolyte, 20 mg of water is enough to consume about 169 mg of salt. The technical limit assumes the solvent will be used where moisture is tolerable.
Is DMC a drop-in replacement for dimethyl sulfate?
In safety terms yes, in process terms no. DMC is much less acutely toxic and produces methanol and CO2 rather than sulfate waste, but it needs higher temperature, pressure or catalysis, and it is not suitable for every methylation.
Can I dry technical grade down to battery grade myself?
Not economically. Water can be reduced by drying, but the colour specification cannot be recovered once the product has met a hot surface or a contaminated line; battery grade is defined by all three limits at once.
What is the shelf life?
Twelve months in unopened drums under the stated conditions, with the caveat that every opening admits moisture. Treat the certificate’s values as the state at packing, and re-test if a drum has been open for months.
Which grade for a pharmaceutical process?
High purity, and then confirm the residual solvent position against ICH Q3C for your product – methanol is a class 2 solvent with a defined limit, and DMC itself should be assessed as a class 3 solvent in the final drug substance.
References and scope note
Physical properties and identity data are cross-checked against public chemical databases (PubChem CID 12021); stoichiometric arithmetic is reproducible from standard atomic weights. Reaction schemes shown are the established commercial routes for orientation, not validated process instructions. No safety, health or environmental claims are made beyond the hazard classification stated.
Technical and commercial orientation only. It is not a substitute for regulatory advice, hazard assessment or a site-specific risk review.
PolyBlueChem supplies all three grades of dimethyl carbonate – battery, high purity and technical – with lot-specific certificates. Contact polybluechem@163.com for pricing, drum and ISO quantities, samples or a specification written against your own monograph.