Dimethyl oxalate is an

organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...

with the formula or . It is the dimethyl

ester In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...

oxalic acid Oxalic acid is an organic acid with the systematic name ethanedioic acid and chemical formula , also written as or or . It is the simplest dicarboxylic acid. It is a white crystalline solid that forms a colorless solution in water. Its name i ...

. Dimethyl oxalate is a colorless or white solid that is soluble in water.

Production

Dimethyl oxalate can be obtained by

esterification In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...

of oxalic acid with

methanol Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical compound and the simplest aliphatic Alcohol (chemistry), alcohol, with the chemical formula (a methyl group linked to a hydroxyl group, often ab ...

using

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...

as a

catalyst Catalysis () is the increase in rate of a chemical reaction due to an added substance known as a catalyst (). Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quick ...

: :

\rm 2\ CH_3OH + (CO_2H)_2\ \xrightarrow\ (CO_2CH_3)_2 + 2\ H_2O

Oxidative carbonylation route

The preparation by oxidative carbonylation has attracted interest because it requires only C1 precursors: :

\rm 4 \ CH_3OH + 4 \ CO + O_2 \xrightarrow\ 2 \ (CO_2CH_3)_2 + 2 \ H_2O

The reaction is catalyzed by Pd²⁺.E. Amadio
''Oxidative Carbonylation of Alkanols Catalyzed by Pd(II)-Phosphine Complexes''
PhD Thesis, Ca'Foscari University Venice, 2009 The synthesis gas is mostly obtained from

coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other Chemical element, elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal i ...

biomass Biomass is a term used in several contexts: in the context of ecology it means living organisms, and in the context of bioenergy it means matter from recently living (but now dead) organisms. In the latter context, there are variations in how ...

. The oxidation proceeds via dinitrogen trioxide, which is formed according to (1) of nitrogen monoxide and

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

and then reacts according to (2) with methanol forming

methyl nitrite Methyl nitrite is an organic compound with the chemical formula . It is a gas, and is the simplest alkyl nitrite. Structure At room temperature, methyl nitrite exists as a mixture of ''cis'' and ''trans'' conformers. The ''cis'' conformer i ...

:X.-Z. Jiang, ''Palladium Supported Catalysts in CO + RONO Reactions'', Platinum Metals Rev., 1990, 34, (4), 178–180 : Methylnitrite Synthesis

In the next step of dicarbonylation (3)

carbon monoxide Carbon monoxide (chemical formula CO) is a poisonous, flammable gas that is colorless, odorless, tasteless, and slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the si ...

reacts with methyl nitrite to dimethyl oxalate in the vapor phase at atmospheric pressure and temperatures at 80-120 °C over a

palladium Palladium is a chemical element; it has symbol Pd and atomic number 46. It is a rare and lustrous silvery-white metal discovered in 1802 by the English chemist William Hyde Wollaston. He named it after the asteroid Pallas (formally 2 Pallas), ...

catalyst: : DMO Synthesis Summary

The sum equation: : DMO from MeOH via oxidative carbonylation

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: : Monocarbonylation of MeOH corr

Alternatively, the oxidative carbonylation of methanol can be carried out with high yield and selectivity with 1,4-benzoquinone as an oxidant in the system Pd(OAc)₂/ PPh₃/benzoquinone with mass ratio 1/3/100 at 65 °C and 70 atm CO: : Oxidative carbonylation with BQ corr

Reactions

Dimethyl oxalate (and the related diethyl ester) is used in diverse

condensation reaction In organic chemistry, a condensation reaction is a type of chemical reaction in which two molecules are combined to form a single molecule, usually with the loss of a small molecule such as water. If water is lost, the reaction is also known as a ...

s. For example, diethyl oxalate condenses with cyclohexanone to give the diketo-ester, a precursor to pimelic acid. With diamines, the diesters of oxalic acid condense to give cyclic diamides. Quinoxalinedione is produced by condensation of dimethyloxalate and o-phenylenediamine: :C₂O₂(OMe)₂ + C₆H₄(NH₂)₂ → C₆H₄(NHCO)₂ + 2 MeOH Hydrogenation gives

ethylene glycol Ethylene glycol ( IUPAC name: ethane-1,2-diol) is an organic compound (a vicinal diol) with the formula . It is mainly used for two purposes: as a raw material in the manufacture of polyester fibers and for antifreeze formulations. It is an odo ...

. Dimethyl oxalate can be converted into ethylene glycol in high yields (94.7%) : MEG from DMO

The methanol formed is recycled in the process of oxidative carbonylation. Other plants with a total annual capacity of more than 1 million tons of ethylene glycol per year are planned. Decarbonylation gives

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 as a co-solvent in lithium-ion ba ...

. :

Diphenyl oxalate is obtained by

transesterification Transesterification is the process of exchanging the organic functional group R″ of an ester with the organic group R' of an alcohol. These reactions are often catalyzed by the addition of an acid or base catalyst. Strong acids catalyze the r ...

with

phenol Phenol (also known as carbolic acid, phenolic acid, or benzenol) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile and can catch fire. The molecule consists of a phenyl group () ...

in the presence of titanium catalysts, which is again decarbonylated to diphenyl carbonate in the liquid or gas phase. Dimethyl oxalate can also be used as a methylating agent. It is notably less toxic than other methylating agents such as

methyl iodide Iodomethane, also called methyl iodide, and commonly abbreviated "MeI", is the chemical compound with the formula CH3I. It is a dense, colorless, volatile liquid. In terms of chemical structure, it is related to methane by replacement of one h ...

dimethyl sulfate Dimethyl sulfate (DMS) is a chemical compound with formula (CH3O)2SO2. As the diester of methanol and sulfuric acid, its formula is often written as ( CH3)2 SO4 or Me2SO4, where CH3 or Me is methyl. Me2SO4 is mainly used as a methylating agen ...

References

{{Reflist Oxalate esters Methyl esters