dimethyl oxalate

Dimethyl oxalate can be obtained by esterification of oxalic acid with methanol using sulfuric acid as a catalyst:{{cite journal |doi=10.15227/orgsyn.010.0078|title=Methyl Oxalate|journal=Organic Syntheses|year=1930|volume=10|page=78|author=Everett Bowden}}

:$\backslash rm\; 2\backslash \; CH\_3OH\; +\; (CO\_2H)\_2\backslash \; \backslash xrightarrow\{H\_2SO\_4\}\backslash \; (CO\_2CH\_3)\_2\; +\; 2\backslash \; H\_2O$

The preparation by oxidative carbonylation has attracted interest because it requires only C1 precursors:Hans-Jürgen Arpe: Industrielle Organische Chemie: Bedeutende Vor- und Zwischenprodukte, S. 168; {{ISBN|978-3-527-31540-6}}.

:$\backslash rm\; 4\; \backslash \; CH\_3OH\; +\; 4\; \backslash \; CO\; +\; O\_2\; \backslash xrightarrow\{catalyst\}\backslash \; 2\; \backslash \; (CO\_2CH\_3)\_2\; +\; 2\; \backslash \; H\_2O$

The reaction is catalyzed by Pd²⁺.{{cite patent| country = US| number = 4467109| title = Process for Continuous preparation of diester of oxalic acid| gdate = 1983-05-19| fdate = 1984-08-21| inventor =Susumu Tahara et al.| assign1 = Ube Industries}} and {{cite patent| country = EP| number = 108359| title = Process for the preparation of a diester of oxalic acid| fdate = 1984-05-16| inventor = K. Masunaga et al.| assign1 = Ube Industries}}{{cite patent| country = EP| number = 425197| title = Process for preparing diester of carbonic acid| pubdate = 1991-05-2| invent1 = K. Nishihira| invent2 = K. Mizutare| assign1 = Ube Industries}}{{cite patent| country = US| number = 4451666| title = Synthesis of oxalate esters by the oxidative carbonylation of alcohols| pubdate = 1984-05-29| inventor =J.A. Sofranko, A.M. Gaffney| assign1 = Atlantic Richfield Co.}}E. Amadio: [http://dspace.unive.it/bitstream/handle/10579/946/Amadio%20Emanuele_955382_thesis.pdf 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 or biomass. The oxidation proceeds via dinitrogen trioxide, which is formed according to (1) of nitrogen monoxide and oxygen and then reacts according to (2) with methanol forming methyl nitrite:X.-Z. Jiang, Palladium Supported Catalysts in CO + RONO Reactions, Platinum Metals Rev., 1990, 34, (4), 178–180

:Methylnitrit-Synthese

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 a palladium catalyst:

:DMO-Synthese zusammengefasst

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

Dimethyl oxalate (and the related diethyl ester) is used in diverse condensation reactions.{{cite journal |doi=10.1016/S0040-4020(01)87933-3|title=Alkylation with Oxalic Esters. Scope and mechanism|year=1990|last1=Bergman|first1=Jan|last2=Norrby|first2=Per-Ola|last3=Sand|first3=Peter|journal=Tetrahedron|volume=46|issue=17|pages=6113–6124|s2cid=94945519}} For example, diethyl oxalate condenses with cyclohexanone to give the diketo-ester, a precursor to pimelic acid.{{cite journal|author=H. R. Snyder |author2=L. A. Brooks |author3=S. H. Shapiro |author4=A. Müller |title=Pimelic Acid|journal=Organic Syntheses|volume=11|page=42|year=1931|doi=10.15227/orgsyn.011.0042}} 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.Nexant/Chemsystems, {{cite web |url=http://www.chemsystems.com/reports/search/docs/prospectus/stmc10_coal_meg.pdf |title=Coal to MEG, Changing the Rules of the Game |access-date=2016-08-08 |url-status=bot: unknown |archive-url=https://web.archive.org/web/20110714135349/http://www.chemsystems.com/reports/search/docs/prospectus/stmc10_coal_meg.pdf |archive-date=July 14, 2011}} (PDF; 5,4 MB), 2011 Prospectus Dimethyl oxalate can be converted into ethylene glycol in high yields (94.7%){{cite patent| country = EP| number = 046 983| title = Process for continuously preparing ethylene glycol| fdate = 1982-03-10| invent1 = S. Tahara et al.| assign1 = Ube Industries}} and H. T. Teunissen and C. J. Elsevier, Ruthenium catalyzed hydrogenation of dimethyl oxalate to ethylene glycol, J. Chem. Soc., Chem. Commun., 1997, 667-668), DOI:10.1039/A700862G.S. Zhang et al., Highly-Dispersed Copper-Based Catalysts from Cu–Zn–Al Layered Double Hydroxide Precursor for Gas-Phase Hydrogenation of Dimethyl Oxalate to Ethylene Glycol, Catalysis Letters, Sept. 2012, 142 (9), 1121–1127, DOI:10.1007/s10562-012-0871-8

:MEG from DMO

The methanol formed is recycled in the process of oxidative carbonylation.{{Cite web|url=http://www.icis.com/resources/news/2012/01/30/9527520/china-s-coal-based-chemicals-are-a-trade-off/|title=Individual news}} Other plants with a total annual capacity of more than 1 million tons of ethylene glycol per year are planned.

Decarbonylation gives dimethyl carbonate.{{cite patent| country = US| number = 4544507| title = Production of carbonate diesters from oxalate diesters| fdate = 1985-10-01| inventor =P. Foley| assign1 = Celanese Corp}}

:DMC from DMO

Diphenyl oxalate is obtained by transesterification with phenol in the presence of titanium catalysts,{{cite patent| country = US| number = 5834614| title = Process for producing diaryl carbonate| fdate = 1998-11-10| inventor =K. Nishihira et al.| assign1 = Ube Industries, Ltd.}} and X.B. Ma et al., Preparation of Diphenyl Oxalate from Transesterification of Dimethyl Oxalate with Phenol over TS-1 Catalyst, Chinese Chem. Lett., 14 (5), 461–464 (2003), DOI:10.1016/s0378-3820(03)00075-4. 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 or dimethyl sulfate.{{Cite journal |last1=Bergman |first1=Jan |last2=Norrby |first2=Per-Ola |last3=Sand |first3=Peter |date=1990-01-01 |title=Alkylation with Oxalic Esters. Scope and mechanism |url=https://www.sciencedirect.com/science/article/pii/S0040402001879333 |journal=Tetrahedron |language=en |volume=46 |issue=17 |pages=6113–6124 |doi=10.1016/S0040-4020(01)87933-3 |s2cid=94945519 |issn=0040-4020|url-access=subscription }}

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Category:Oxalate esters

Category:Methyl esters