Study On The Application Of Dimethyl Carbonate In Green Catalytic Reactions

Dimethyl carbonate (DMC), a non-toxic and environmentally benign chemical, is a safe substitute for dimethyl sulfate, methyl halide and phosgene. DMC has a versatile chemical property and has been used mainly as a methylating and methoxycarbonylating agent. This dissertation is focused on the application of DMC in some green catalytic reactions.A facile synthesis of N,N-dimethylanilines from primary aromatic amines and DMC has been achieved for the first time in the presence of diphenylammonium triflate (DPAT). N,N-dimethylanilines were selectively obtained in high yields. Detailed studies have been performed using aniline as a substrate. The conversion of aniline and the selectivity to N,N-dimethylaniline was 99.9% and 99.6%, respectively, under optimized reaction conditions. The experimental results revealed that the presence of substituting groups on the benzene ring would affect the activity of primary aromatic amines. In the reaction, aniline would react with DPAT to form a complex containing a nucleophilic anion. This intermediate could react with DMC via direct B_Al2 displacement to generate N-methylaniline. N-methylaniline underwent the same B_Al2 displacement to generate N,N-dimethylaniline.A direct one-pot synthesis of N-methyl-N-aryl carbamates from aromatic amines and DMC has been achieved with high yields in the presence of potassium carbonate (K₂CO₃) and tetrabutylammonium bromide (Bu4NBr) under solvent-free conditions. All the reaction parameters were examined in the reaction of aniline with dimethyl carbonate. Under optimized reaction conditions, the conversion of aniline was 99.7% and the yield of methyl N-methyl-N-phenyl carbamate was 83.2%. The benzene ring with electron-withdrawing groups gave excellent yields. On the contrary, the existence of electron-donating groups on the benzene ring would prolong reaction times and decrease the yields. Based on the experimental results, it could be consequentially concluded that N-methoxycarbonylation of aromatic amines was followed by the exclusive N-methylation of methyl N-aryl carbamates during the reaction process.A new transesterification for preparing ethyl methyl carbonate from DMC and diethyl carbonate was carried out in the presence of solid basic catalysts both in the liquid and the vapor phase. Among the catalysts examined, MgO was the most active catalyst. Basic properties of the solid catalysts were measured by temperature programmed desorption of CO₂. The results revealed that the moderately basic sites on the catalysts play a crucial role in catalytic performance. Homogeneous catalysts, titanate and organic tin compounds, also showed good catalytic performance in this reaction. The possible...