Dimethyl carbonate

Dimethyl carbonate (DMC) is an organic compound with the formula OC(OCH3)2. It is a colourless, flammable liquid. It is classified as a carbonate ester. This compound has found use as a methylating agent and more recently as a solvent that is exempt from the restrictions placed on most volatile organic compounds (VOCs) in the US.[1] Dimethyl carbonate is often considered to be a green reagent.[2]

Not to be confused with dimethyl carbate.
Dimethyl carbonate
Names
IUPAC name
Dimethyl carbonate
Other names
DMC
Methyl carbonate
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.009.527
UNII
Properties
C3H6O3
Molar mass 90.078 g·mol−1
Appearance Clear liquid
Density 1.069-1.073 g/mL
Melting point 2 to 4 °C (36 to 39 °F; 275 to 277 K)
Boiling point 90 °C (194 °F; 363 K)
13.9 g/100 mL
Hazards
Main hazards Flammable
Flash point 17 °C (63 °F; 290 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Production

World production in 1997 was estimated at 1000 barrels a day.[3] Production of dimethyl carbonate worldwide is limited to Asia, the Middle East, and Europe.

Dimethyl carbonate is traditionally prepared by the reaction of phosgene and methanol. Methyl chloroformate is produced as an intermediate:

COCl2 + CH3OH → CH3OCOCl + HCl
CH3OCOCl + CH3OH → CH3OCO2CH3 + HCl

This synthesis route has been largely replaced by oxidative carbonylation. In this process, carbon monoxide and an oxidizer provide the equivalent of CO2+:[4][5]

CO + 1/2 O2 + 2 CH3OH → (CH3O)2CO + H2O

It can also be produced industrially by a transesterification of ethylene carbonate or propylene carbonate and methanol, which also affords respectively ethylene glycol or propylene glycol.

Reactions and potential applications

Methylating agent

Dimethyl carbonate methylates anilines, phenols, and carboxylic acids, but many of these reactions require the use of an autoclave.[6][7]

Dimethyl carbonate's main benefit over other methylating reagents such as iodomethane and dimethyl sulfate is its low toxicity. Additionally, it is biodegradable.[4] Unfortunately, it is a relatively weak methylating agent compared to these traditional reagents.

Solvent

In the US, dimethyl carbonate was exempted under the definition of volatile organic compounds (VOCs) by the U.S. EPA in 2009.[8] Due to its classification as VOC exempt, dimethyl carbonate has grown in popularity and applications as a replacement for methyl ethyl ketone (MEK) and parachlorobenzotrifluoride, as well as tert-butyl acetate until it too was exempted.[9] Dimethyl carbonate has an ester- or alcohol-like odor, which is more favorable to users than most hydrocarbon solvents it replaces. Dimethyl carbonate has an evaporation rate of 3.22 (butyl acetate = 1.0), which slightly slower than MEK (3.8) and ethyl acetate (4.1), and faster than toluene (2.0) and isopropanol (1.7). Dimethyl carbonate has solubility profile similar to common glycol ethers, meaning dimethyl carbonate can dissolve most common coating resins except perhaps rubber based resins. Hildebrand solubility parameter is 20.3 MPa and Hansen solubility parameters are: dispersion = 15.5, polar = 3.9, H bonding = 9.7.[10] Dimethyl carbonate is partially soluble in water up to 13%, however it is hydrolyzed in water-based systems over time to methanol and CO2 unless properly buffered. Dimethyl carbonate can freeze at same temperatures as water, it can be thawed out with no loss of properties to itself or coatings based on dimethyl carbonate.

Intermediate in polycarbonate synthesis

A large captive use of dimethyl carbonate is for the production of diphenyl carbonate through transesterification with phenol. Diphenyl carbonate is a widely used raw material for the synthesis of bisphenol-A-polycarbonate in a melt polycondensation process. The most common route is described by Fukuoka, of the Japanese "Asahi Kasei" chemical corporation.[11]

Alternative fuel additive

There is also interest in using this compound as a fuel oxygenate additive.[3]

Safety

DMC is a flammable liquid with a flash point of 17 °C (63 °F), which limits its use in consumer and indoor applications. DMC is still safer than acetone, methyl acetate and methyl ethyl ketone from a flammability point of view. DMC has a recommended exposure limit (REL) limit of 100 ppm by inhalation over an 8-hour work day, which is similar to that of a number of common industrial solvents (toluene, methyl ethyl ketone). Workers should wear protective organic vapor respirators when using DMC indoors or in other conditions where concentrations exceed the REL. DMC is metabolized by the body to methanol and carbon dioxide, so accidental ingestion should be treated in the same manner as methanol poisoning.

See also

References
  1. "Update: U.S. EPA Exempt Volatile Organic Compounds". American Coatings Association. 2018-01-30. Retrieved 2019-03-20.
  2. Kreutzberger, Charles B. (2001), "Chloroformates and Carbonates", Kirk-Othmer Encyclopedia of Chemical Technology, New York: John Wiley, doi:10.1002/0471238961.0301180204011312.a01.pub2, ISBN 9780471238966
  3. Pacheco, Michael A.; Marshall, Christopher L. (1997). "Review of Dimethyl Carbonate (DMC) Manufacture and Its Characteristics as a Fuel Additive". Energy Fuels. 11: 2–29. doi:10.1021/ef9600974.
  4. Pietro Tundo & Maurizio Selva (2002). "The Chemistry of Dimethyl Carbonate". Acc. Chem. Res. 35 (9): 706–16. doi:10.1021/ar010076f. PMID 12234200.
  5. Hans-Josef Buysch. "Carbonic Esters". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a05_197/full.
  6. Shieh, Wen-Chung; Dell, Stephen; Repič, Oljan (2002). "Nucleophilic Catalysis with 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) for the Esterification of Carboxylic Acids with Dimethyl Carbonate". J. Org. Chem. 67 (7): 2188–2191. doi:10.1021/jo011036s. PMID 11925227.
  7. Shieh, Wen-Chung; Dell, Steven; Repič, Oljan (2001). "1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) and Microwave-Accelerated Green Chemistry in Methylation of Phenols, Indoles, and Benzimidazoles with Dimethyl Carbonate". Organic Letters. 3 (26): 4279–81. doi:10.1021/ol016949n. PMID 11784197.
  8. http://www.epa.gov/ttn/oarpg/t1/fact_sheets/voc_exemp01011309.pdf. Information about the EPA's action on exempting dimethyl carbonate as a VOC and petitioner's background information, public comments and other references are available electronically at http://www.regulations.gov, EPA’s electronic public docket and comment system. The docket number for this action is Docket ID No. EPA-HQ-OAR-2006-0948. See http://www.epa.gov/ttn/oarpg/t1pfpr.html and scroll down to Jan 13, 2009 pdf for the rule.
  9. "Update: U.S. EPA Exempt Volatile Organic Compounds". American Coatings Association. 2018-01-30. Retrieved June 23, 2020.
  10. Kanegsberg, Barbara; Kanegsberg, Edward (2011-04-04). Handbook for Critical Cleaning: Cleaning Agents and Systems, Second Edition (Second ed.). CRC Press. p. 16. ISBN 9781439828281.
  11. Non phosgene Polycarbonate from CO2 - Industrialization of Green Chemical Process, Shinsuke Fukuoka (Asahi Kasei Chemicals Corporation)
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