Dimethyl oxalate is the

organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. The s ...

with the formula (CO₂CH₃)₂. It is the

dimethyl Ethane ( , ) is an organic chemical compound with chemical formula . At standard temperature and pressure, ethane is a colorless, odorless gas. Like many hydrocarbons, ethane is isolated on an industrial scale from natural gas and as a petr ...

ester In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides are f ...

oxalic acid Oxalic acid is an organic acid with the systematic name ethanedioic acid and formula . It is the simplest dicarboxylic acid. It is a white crystalline solid that forms a colorless solution in water. Its name comes from the fact that early investi ...

. 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 oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides are ...

of oxalic acid with

methanol Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical and the simplest aliphatic alcohol, with the formula C H3 O H (a methyl group linked to a hydroxyl group, often abbreviated as MeOH). It is a lig ...

using

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

as a

catalyst Catalysis () is the process of increasing the reaction rate, rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the ...

: :

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

Oxidative carbonylation route

The preparation by

oxidative carbonylation Oxidative carbonylation is a class of reactions that use carbon monoxide in combination with an oxidant to generate esters and carbonate esters. These transformations utilize transition metal complexes as homogeneous catalysts. Many of these react ...

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 elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when dead ...

or biomass. The oxidation proceeds via

dinitrogen trioxide Dinitrogen trioxide is the chemical compound with the formula N2O3. It is one of the simple nitrogen oxides. It forms upon mixing equal parts of nitric oxide and nitrogen dioxide and cooling the mixture below −21 °C (−6 °F): :NO + ...

, which is formed according to (1) of

nitrogen monoxide Nitric oxide (nitrogen oxide or nitrogen monoxide) is a colorless gas with the formula . It is one of the principal oxides of nitrogen. Nitric oxide is a free radical: it has an unpaired electron, which is sometimes denoted by a dot in its ch ...

and

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as well ...

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 is ...

: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 colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simpl ...

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 with the symbol Pd and atomic number 46. It is a rare and lustrous silvery-white metal discovered in 1803 by the English chemist William Hyde Wollaston. He named it after the asteroid Pallas, which was itself na ...

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 1,4-Benzoquinone, commonly known as ''para''-quinone, is a chemical compound with the formula C6H4O2. In a pure state, it forms bright-yellow crystals with a characteristic irritating odor, resembling that of chlorine, bleach, and hot plastic or ...

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 Quinoxalinedione is an organic compound with the formula C6H4(NH)2(CO)2. It is a colorless solid that is soluble in polar organic solvents. Quinoxalinediones are a family of related compounds sharing the same bicyclic core. Various quinoxalinedi ...

is produced by condensation of dimethyloxalate and

o-phenylenediamine ''o''-Phenylenediamine (OPD) is an organic compound with the formula C6H4(NH2)2. This aromatic diamine is an important precursor to many heterocyclic compounds. It is isomeric with ''m''-phenylenediamine and ''p''-phenylenediamine. Preparation ...

: :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 more recently as a solvent that is e ...

. :

Diphenyl oxalate is obtained by

transesterification In organic chemistry, transesterification is the process of exchanging the organic 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. The reaction can ...

with

phenol Phenol (also called carbolic acid) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile. The molecule consists of a phenyl group () bonded to a hydroxy group (). Mildly acidic, it requir ...

in the presence of titanium catalysts, which is again decarbonylated to

diphenyl carbonate Diphenyl carbonate is the organic compound with the formula (C6H5O)2CO. It is classified as an acyclic carbonate ester. It is a colorless solid. It is both a monomer in combination with bisphenol A in the production of polycarbonate polymers a ...

in the liquid or gas phase. Dimethyl oxalate can also be used as a

methylating agent In the chemical sciences, methylation denotes the addition of a methyl group on a substrate, or the substitution of an atom (or group) by a methyl group. Methylation is a form of alkylation, with a methyl group replacing a hydrogen atom. These t ...

. 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 agent ...

References

{{Reflist Oxalate esters Methyl esters