Synthesis Of Dimethyl Carbonate From Oxidative Carbonylation Of Methanol Catalyzed By Copper Complex Without Chloride

Dimethyl carbonate （DMC） is attracted with high attention due to its active chemicalproperty, broad use and low toxicity. The mainly synthesized methods for DMC containedthe phosgene, the ester exchange, the oxidative carbonylation of methanol. The oxidativecarbonylation of methanol to DMC has become the main research methods because of theinexpensive materials, simple and clean process. Traditional catalysis CuCl in the synthesisof DMC from oxidative carbonylation of methanol performed serious corrosion of chlorineand inactivation for the loss of chlorine though the activity is relatively high. Measures,such as loading and adding promoter or ligands, were adopted and the catalytic activity andanticorrosive were improved to a certain extent, but the fundamental problems remained.Halogen-free copper complexes were prepared with1,10-Philippines （phen） asligand and copper acetate and methoxyl copper as active component replace the cupricchloride and cuprous chloride. Besides, novel copper complexs were prepared when theimidazole and its derivatives were synthesized as ligands and chelated with copper acetate.Halogen-free copper complexes were characterized with thermogravimetric analysis andinfrared spectrum analysis, ultraviolet spectrum analysis. Infrared spectroscopy andnuclear magnetic resonance （NMR） analysis were used for the characterization of theimidazole and its derivatives. The effect of the technological conditions including reactiontemperature, reaction time and amount of the catalyst on the oxidative carbonylation werediscussed. The process influenced the activity were also analyzed.（1） The acetate copper complexes were preparaed with acetate copper and ligandsincluding phen and DMe-H₂biim. Most of acetate moiety in complexes was displaced bymethoxyl came from activation of methanol, forming copper methoxy active species. Theby-product acetate acid was esterized into methyl acetate with methanol.（2） When the synthesis of DMC from oxidative carbonylation of methanol catalyzedby Cu₂（OAc）₄（phen）₂（H₂O） was carried out in the condition of catalyst concentration0.014mol/L, reaction time4h, reaction temperature120℃, the DMC turn over numberwas33.0mol_DMC/mol_CuDMCand the DMC selectivity reached98.1%, and most of acetate moiety was lost by turning into methyl acetate. However, the DMC turn over numberdecreased to16.7mol_DMC/mol_Cuin the reuse reaction. It is possible that the procedureCu（II）（OCH3） species and Cu（I）（CO） species converted to Cu（II）（COOCH3） species via aCu（I, II） species bridged by acetate moiety became more difficult for the loss of acetatemoiety, so the recycle reaction shown a depression of catalytic activity.（3） Among the complexes with acetate copper as source of copper and H₂biim,DMe-H₂biim, oxy-H₂biim as ligands, Cu（OAc）₂-H₂biim shown the lowest activity due tothe poor solibility; Cu（OAc）₂-oxy-H₂biim turned out relatively poor activity in that theelectronic effect of benzene ring weaken the σ-π coordination bong between ligand andcopper; The restrictive effect of methylene in DMe-H₂biim make the complex to be plane.Moreover, the weak electrical effects strengthen the σ-π coordination bong betweenligand and copper. So Cu（OAc）₂-DMe-H₂biim performed the best acivity and the DMCturn over number was20.2mol_DMC/mol_CuDMCand the DMC selectivity94.8%in thecondition of catalyst concentration0.014mol/L, reaction time4h, reaction temperature110℃.（4） When the oxidative carbonylation of methanol was catalyzed by Copper （II）methoxide and chloride Copper （II） methoxide, the DMC turn over number were12.9mol_DMC/mol_Cuand11.7mol_DMC/mol_Curespectively. They increased to23.6mol_DMC/mol_Cuand15.5mol_DMC/mol_Cuwhen Copper （II） methoxide and chlorideCopper （II） methoxide mixed with phen.