Research On One-Oot Synthesis Of DMC Catalyzed By Organic Ionic Liquids

Dimethyl carbonate (DMC) is one of the most important intermediates in organicsynthesis with low toxicity and versatile chemical properties. The transesterificationprocess is one of the few industrial routes for synthesis of DMC, during which DMC issynthesised through transesterification from CH3OH and cyclic carbonate, and thecyclic carbonate can be produced by cycloaddition between CO2and epoxide.Compared with the two-step transesterification route, one-step synthesis of DMCdirectly from CO2, epoxide, and CH3OH has advantages of shorter process flows, moresimple devices, lower energy consumption and less cost on product separation.Therefore, it’s a process of green and economy.In recent years, numerous functionalized ionic liquids are widely applicated in thecatalytic field. In present work, a new type of catalyst was prepared from polyethyleneglycols (PEG) and1-butyl-3-methyl-imimidazolium ionic liquids by heating theirmixture directly. DMC was produced in one-step from CO2, PO, and CH3OH withonce-through yield of41.1%, and selectivity reached89.16%. What’s more, the reactionprocesses were studied at the B3LYP/6-311G**level by Gaussian, and a possiblereaction mechanism was proposed. Conclusions could be listed as follows:①Two different catalysts, the Catalyst A and Catalyst B, were preparedwith/without H2O by eutectic melting method, Catalyst A can catalyze the synthesis ofDMC effectively, while Catalyst B has no catalytic effects on the synthesis of DMC. Inthe molecular structure of Catalyst A, PEG was bonding to carbon atom of the C=N inimidazole ring, forming a C-O, the C=N turned into C-N, and the PEG’s original C-C-Obone structure was maintained without changes of the original butyl group and methylgroup in the imidazole ring. While in the molecular structure of Catalyst B, when thePEG was bonding to carbon atom of the C=N in imidazole ring, the butylgroup bondedto the N was lost simultaneously, forming secondary amine-NH-, and the methyl groupin the imidazole ring was keeped.②Structures of the catalyst were optimized systematically, and the effects ofdifferent reaction conditions were studied. The results indicated that catalysts preparedfrom PEG of low polymerization degree（Molecular mass:400-1000）and [Bmim]Cl inthe mole ratio of almost2:1exhibited the best catalytic performance. And with theincrease of initial pressure of CO2, both the yield and selectivity of DMC increase firstly and then decrease; with the increase of reaction time, the yield of DMC increase firstly,and then keep balance, while the selectivity increase firstly and then decrease before thebalance; both the yield and selectivity of DMC increase firstly and then decrease withthe increase of the temperature. The optimum conditions for synthesis of DMC weredetermined as follows: initial CO2pressure2-3MPa, reaction temperature140℃,reaction time3h.③The mechanism of catalytic reaction was analyzed by Gaussian. The resultsshowed that either of the Catalyst A and Catalyst B can reduce the energies of of thetransition states respectively by forming hydrogen bonds to reaction substrates. Whilefrom the preliminary results of theoretical calculations, similar relative energies of thetransition states in the two catalysts were figured out, being far from the experimentalresults. So, study on the mechanisms for synthesis of DMC in one-step needs furtherefforts.