Dimethyl carbonate

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Not to be confused with dimethyl carbate. ‹See Tfd›
Dimethyl carbonate
Dimethyl carbonate
Ball-and-stick model of dimethyl carbonate
Identifiers
CAS number 616-38-6 YesY
PubChem 12021
ChemSpider 11526 YesY
ChEBI CHEBI:36596 YesY
Jmol-3D images Image 1
Properties
Molecular formula C3H6O3
Molar mass 90.08 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)
Solubility in water 13.9 g/100 mL
Hazards
Main hazards Flammable
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

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 classification as a volatile organic compound (VOC) in the US. Dimethyl carbonate is often considered to be a green reagent.[1]

Production[edit]

Dimethyl carbonate can be prepared by the reaction of phosgene with methanol via methyl chloroformate:

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

Overall:

COCl2 + 2 CH3OH → CH3OCO2CH3 + 2 HCl

This historical synthesis process is undesirable because of phosgene's toxicity and has been largely replaced by other synthesis routes. It is produced industrially by a transesterification of propylene carbonate and methanol, which also affords propylene glycol. A second large scale commercial synthesis route uses a process where carbon monoxide, methanol and oxygen are reacted to form dimethyl carbonate.[2] World production in 1997 was estimated at 1000 barrels a day.[3] Production of dimethyl carbonate worldwide is limited to Asia and Europe.

Reactions and potential applications[edit]

Methylating agent[edit]

Dimethyl carbonate methylates anilines, phenols and carboxylic acids, but many of these reactions require the use of an autoclave.[4][5] and the preparation of methyl carboxylate esters:[4]

Methylation of phenylacetic acid by dimethyl carbonate promoted by DBU

Dimethyl carbonate's main benefit over other methylating reagents such as iodomethane and dimethyl sulfate is its much lower toxicity and its biodegradability.[2] Unfortunately, it is a relatively weak methylating agent compared to these traditional reagents.

Solvent[edit]

In the US, DMC was exempted under the definition of volatile organic compounds by the U.S. EPA in 2009.[6] Due to its classification as VOC exempt, dimethyl carbonate has grown in popularity and applications as a replacement for methyl ethyl ketone, tert-butyl acetate, and parachlorobenzotrifluoride. DMC has an ester or alcohol like odor, which is more favorable to users than most hydrocarbon solvents it replaces. DMC has an evaporation rate of 3.22 (butyl acetate = 1.0), which slightly slower than MEK (3.8) & Ethyl Acetate (4.1) and faster than toluene (2.0) & isopropanol (1.7). DMC has solubility profile similar to common glycol ethers, meaning DMC can solve 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. DMC is partially soluble in water up to 13%, however DMC has hydrolyzed in water based systems over time to methanol and CO2 unless properly buffered.

Safety

DMC is a flammable liquid that has a flash point of 17 °C (63 °F), which would limit its use in consumer and indoor applications, DMC is still safer than acetone, methyl acetate and MEK from a flammability point of view. DMC has an recommended industrial exposure (REL) limit of 100 ppm by inhalation over an 8 hour work day, which is similar to a number of common industrial solvents (Toluene, MEK). 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. DMC can freeze at same temperatures as water, it can be thawed out with no loss of properties to itself or coatings based on DMC.

Alternative fuel additive[edit]

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

References[edit]

  1. ^ 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 
  2. ^ a b Pietro Tundo and Maurizio Selva (2002). "The Chemistry of Dimethyl Carbonate". Acc. Chem. Res. 35 (9): 706–16. doi:10.1021/ar010076f. 
  3. ^ a b 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. ^ a b 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. 
  5. ^ 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. 
  6. ^ 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.