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| Names | |
|---|---|
| Preferred IUPAC name Dimethyl oxalate | |
| Identifiers | |
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3D model (JSmol) | |
| ChemSpider | |
| ECHA InfoCard | 100.008.231 |
| UNII | |
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| Properties | |
| C4H6O4 | |
| Molar mass | 118.088 g·mol−1 |
| Appearance | White crystals |
| Melting point | 53 to 55 °C (127 to 131 °F; 326 to 328 K)[1] |
| Boiling point | 166 to 167 °C (331 to 333 °F; 439 to 440 K)[1] |
| −55.7·10−6 cm3/mol | |
| Related compounds | |
Related compounds | Diethyl oxalate,Diphenyl oxalate |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Dimethyl oxalate is anorganic compound with the formula(CO2CH3)2 or(CH3)2C2O4. It is thedimethylester ofoxalic acid. Dimethyl oxalate is a colorless or white solid that is soluble in water.
Dimethyl oxalate can be obtained byesterification of oxalic acid withmethanol usingsulfuric acid as acatalyst:[2]
The preparation byoxidative carbonylation has attracted interest because it requires onlyC1 precursors:[3]
The reaction is catalyzed by Pd2+.[4][5] The synthesis gas is mostly obtained fromcoal orbiomass. The oxidation proceeds viadinitrogen trioxide, which is formed according to (1) ofnitrogen monoxide andoxygen and then reacts according to (2) with methanol formingmethyl nitrite:[6]
In the next step of dicarbonylation (3)carbon monoxide reacts with methyl nitrite to dimethyl oxalate in the vapor phase at atmospheric pressure and temperatures at 80-120 °C over apalladium catalyst:
The sum equation:
This method is lossless with respect to methyl nitrite, which acts practically as a carrier of oxidation equivalents. However, the water formed must be removed to prevent hydrolysis of the dimethyl oxalate product. With 1% Pd/α-Al2O3 dimethyl oxalate is produced selectively in a dicarbonylation reaction, under the same conditions with 2% Pd/C dimethyl carbonate is produced by monocarbonylation:
Alternatively, the oxidative carbonylation of methanol can be carried out with high yield and selectivity with1,4-benzoquinone as an oxidant in the systemPd(OAc)2/PPh3/benzoquinone with mass ratio 1/3/100 at 65 °C and 70 atmCO:[5]
Dimethyl oxalate (and the related diethyl ester) is used in diversecondensation reactions.[7] For example, diethyl oxalate condenses withcyclohexanone to give the diketo-ester, a precursor to pimelic acid.[8] With diamines, the diesters of oxalic acid condense to give cyclic diamides.Quinoxalinedione is produced by condensation of dimethyloxalate ando-phenylenediamine:
Hydrogenation givesethylene glycol.[9] Dimethyl oxalate can be converted into ethylene glycol in high yields (94.7%)[10][11]
The methanol formed is recycled in the process of oxidative carbonylation.[12] Other plants with a total annual capacity of more than 1 million tons of ethylene glycol per year are planned.
Decarbonylation givesdimethyl carbonate.[13]
Diphenyl oxalate is obtained bytransesterification withphenol in the presence of titanium catalysts,[14] which is again decarbonylated todiphenyl carbonate in the liquid or gas phase.
Dimethyl oxalate can also be used as amethylating agent. It is notably less toxic than other methylating agents such asmethyl iodide ordimethyl sulfate.[7]
{{cite web}}: CS1 maint: bot: original URL status unknown (link) (PDF; 5,4 MB), 2011 Prospectus