Synlett 2008(4): 624-625  
DOI: 10.1055/s-2008-1032048
SPOTLIGHT
© Georg Thieme Verlag Stuttgart · New York

Dimethyl Carbonate (DMC): A Versatile and Environmentally Benign Building Block

Sunay V. Chankeshwara*
Department of Medicinal Chemistry, National Institute of Pharmaceutical Education and Research (NIPER), SAS Nagar, Punjab 160062, India.
e-Mail: sunay_vc@yahoo.com;

Dedicated to Prof. Asit K. Chakraborti


Further Information

Publication History

Publication Date:
12 February 2008 (online)

Biographical Sketches

Sunay V. Chankeshwara was born in 1981. He started studying chemistry in 2002 at the National Institute of Pharmaceutical Education and Research (NIPER), Punjab, India. Currently, he is working towards his PhD thesis under the tutelage of Prof. Asit K. Chakraborti. His primary research interests focus on the synthesis of bioactive small heterocyclic organic molecules and the development of environmentally benign procedures for their synthesis.

Introduction

Dimethyl carbonate (DMC) is a unique molecule with versatile chemical reactivity. In many aspects, DMC is an environmentally benign building block [1] because of its cheap commercial availablility and high ecological safety profile; it possesses interesting solvating properties, low toxicity, and is highly biodegradable. [2]

Preparation

Originally, DMC was synthesized in a clean process of catalytic oxidative carbonylation of methanol in the presence of oxygen. [3] Very recently, DMC was efficiently synthesized from methanol, propylene oxide, and CO2, catalyzed by recyclable organic/inorganic bases (Scheme [1] ).

Scheme 1

The versatile role of DMC as solvent, [4] methoxycarbon­ylation agent, [5] esterification [6] and transesterification agent, [7] green oxidiant [8] and selective methylating agent [9-12] is summarized below.

Abstract

(A) Solvent: Environmentally friendly oxidations of various organic compounds with the H2O2/methyltrioxorhenium (MeReO3, MTO) catalytic system have been performed in dimethyl carbonate as solvent. Oxidations proceeded with good conversions and in good yields. Spectrophotometric analysis demonstrated that the [MeReO(O-O)2] complex was formed in dimethyl carbonate and that it was stable for several days at room temperature. [4]
(B) N-Methoxycarbonylation Agent: Primary and secondary aliphatic amines could react with DMC using ionic liquids as solvent and catalyst to give alkyl carbamates in good yields. [5] The desired solid carbamate could be recovered by simple filtration from the two-layer mixture of DMC and ionic liquid. The formation of N-methylated and deammoniated products was restrained.

(C) Esterification Agent: An environmentally friendly process for the esterification of carboxylic acids with DMC can be accelerated (20-480-fold) by employing a combined strategy of microwave and using DBU as the catalyst. This approach provides synthetic advantages, niches, and upscalability. [6]

(D) Trans-Esterification/Disproportionation Reaction: Diphenyl carbonate (DPC) is considered a substitute for phosgene to synthesize polycarbonate resins. Trans-esterification of DMC with phenol in the presence of titanocene and other titanium complexes yields methyl phenyl carbonate (MPC), which gives DPC by further trans-esterification with DMC or the disproportionation. [7]

(E) Oxidant: In the remarkable reactions where DMC behaves as an oxidant cyclic ketones are transformed into α,ω-dimethyl esters [8] with an atom efficiency of 1.0. [13] DMC has a potential as valuable green oxidant for industrial application in reaction of cyclopentanone and cyclohexanone with DMC (or DEC) and a base (K2CO3) to yield adipic and pimelic methyl (or ethyl) esters, respectively.

(F) N-Methylating Agent: At 130-150 °C and in the presence of K2CO3, o-aminophenol (1) [9] and oximes (2) [10] readily react with di­methyl carbonates to give the corresponding N-methylbenzoxazol-2-ones in high yields. This reaction is a rare example where dialkyl carbonates may simultaneously act as carbonylating and alkylating agents likely via a BAC2/BAL2 sequence. Moreover, DMC also serves as solvent. Methylation with DMC is often very selective and N-methylation of anilines is another example.

(G) O-Methylating Agent: DMC is a safe substitute for dimethyl sulfate or methyl halides. These conventional methylating agents are toxic and corrosive and give a stoichiometric amount of inorganic byproducts. Methylation of catechol with DMC as an alkylating agent has been carried out over calcined Mg-Al hydrotalcites with O-selectivity of 96.1% with a guaiacol selectivity of 84%. [11]

(H) C-Methylating Agent: The most interesting and well-studied reaction, particularly in view of its selectivity, is the mono-C-meth­ylation of arylacetonitriles and methyl arylacetates to produce monomethylated 2-arylpropionitriles and methyl 2-arylpropionates, respectively, with a selectivity of >99.5%. Further, DMC also proved to be the best solvent for such reactions. This reaction is interesting in view of the synthesis of anti-inflammatory drugs. [12]

    References

  • 1 Tundo P. Selva M. Acc. Chem. Res.  2002,  35:  706 
  • 2 Romano U, Rivetti F, and Di Muzio N. inventors; US Patent 4,318,862,  95.  1979; Chem. Abstr. 1981,80141w
  • 3 Tian J.-S. Miao C.-X. Wang J.-Q. Cai F. Du Y. Zhao Y. He L.-N. Green Chem.  2007,  9:  566 
  • 4 Bernini R. Mincione E. Barontini M. Crisante F. Fabrizic G. Gambacortad A. Tetrahedron  2007,  63:  6895 
  • 5 Sima T. Guo S. Shi F. Deng Y. Tetrahedron Lett.  2002,  43:  8145 
  • 6 Shieh W.-C. Dell S. Repi O. Tetrahedron Lett.  2002,  43:  5607 
  • 7 Gong J. Ma X. Wang S. Appl. Catal., A  2007,  316:  1 
  • 8 Selva M. Marques CA. Tundo P. Gazz. Chim. Ital.  1993,  123:  515 
  • 9 Selva M. Synthesis  2003,  2872 
  • 10 Marques CA. Selva M. Tundo P. Montanari F. J. Org. Chem.  1993,  58:  5765 
  • 11 Jyothi TM. Raja T. Talawar MB. Rao BS. Appl. Catal., A  2001,  211:  41 
  • 12a Selva M. Marques CA. Tundo P. J. Chem. Soc., Perkin Trans. 1  1994,  1323 
  • 12b Loosen P, Tundo P, and Selva M. inventors; US Patent  5,278,533.  1994
  • 13 Trost BM. Science  1991,  254:  1471 

    References

  • 1 Tundo P. Selva M. Acc. Chem. Res.  2002,  35:  706 
  • 2 Romano U, Rivetti F, and Di Muzio N. inventors; US Patent 4,318,862,  95.  1979; Chem. Abstr. 1981,80141w
  • 3 Tian J.-S. Miao C.-X. Wang J.-Q. Cai F. Du Y. Zhao Y. He L.-N. Green Chem.  2007,  9:  566 
  • 4 Bernini R. Mincione E. Barontini M. Crisante F. Fabrizic G. Gambacortad A. Tetrahedron  2007,  63:  6895 
  • 5 Sima T. Guo S. Shi F. Deng Y. Tetrahedron Lett.  2002,  43:  8145 
  • 6 Shieh W.-C. Dell S. Repi O. Tetrahedron Lett.  2002,  43:  5607 
  • 7 Gong J. Ma X. Wang S. Appl. Catal., A  2007,  316:  1 
  • 8 Selva M. Marques CA. Tundo P. Gazz. Chim. Ital.  1993,  123:  515 
  • 9 Selva M. Synthesis  2003,  2872 
  • 10 Marques CA. Selva M. Tundo P. Montanari F. J. Org. Chem.  1993,  58:  5765 
  • 11 Jyothi TM. Raja T. Talawar MB. Rao BS. Appl. Catal., A  2001,  211:  41 
  • 12a Selva M. Marques CA. Tundo P. J. Chem. Soc., Perkin Trans. 1  1994,  1323 
  • 12b Loosen P, Tundo P, and Selva M. inventors; US Patent  5,278,533.  1994
  • 13 Trost BM. Science  1991,  254:  1471 

Scheme 1