Heterogenously catalyzed one-step alkylation and carboxylation of N-methylimidazole with dimethyl carbonate in continuous flow

Abstract

The alkylation of N -methylimidazole with dimethyl carbonate yields the respective solid zwitterion N,N ′ -dimethylimidazolium-2-carboxylate, a versatile precursor for manufacturing non-halide-containing ionic liquids (ILs). This reaction requires high p,T-conditions, i.e., up to 200 ° C and 70 bar pressure, and even then requires reaction times up to several days under autoclave batch conditions. To perform these reactions continuously in stainless steel tubes with inner diameters in the millimeter range, precipitation of the salts must be suppressed to avoid any blockage. The achievable yield of the zwitterion is remarkably increased when a packed Al 2 O 3 catalyst is used instead of an empty tube. For example, with a catalyst-packed column, a nearly 100 % yield of N,N ′ -dimethylimidazolium-2-carboxylate can be achieved within 20 min at 200 ° C, whereas only a 67 % yield in 50 min can be obtained without a catalyst at the same temperature. The transfer of the autoclave process into continuous fl ow is advantageous and allows a more economical scale-up.

N‐Heterocyclic Olefin–Carbon Dioxide and –Sulfur Dioxide Adducts: Structures and Interesting Reactivity Patterns

“…Considering the sometimes ambiguous results, it has to be noted that the exact dependence of the product on the reaction conditions is still not fully understood. According to literature reports, imidazolium‐2‐carboxylates can be prepared selectively by feeding gaseous CO 2 into a solution of the corresponding carbene, directly from 1‐methylimidazole and dimethyl carbonate, by continuous flow at 200 °C over an Al 2 O 3 catalyst, and even at ambient temperature by introducing CO 2 into imidazolium acetate ILs . Specifically, the first and last approaches allow extension to imidazolium‐2‐thio‐ and dithiocarboxylates .…”

Use of carbon dioxide as feedstock for chemicals and fuels: homogeneous and heterogeneous catalysis

“…Among linear carbonates the most important are dimethylcarbonate (DMC), diphenylcarbonate (DPC) and diethylcarbonate (DEC). DMC is used in the chemical industry as monomer for polymers, in transesterification reactions for the production of other carbonates such as diphenylcarbonate and others, as alkylating or carboxylating agent . It is also used in the agrochemical and pharmaceutical industry for the production of chemicals or in product formulation.…”

4. Technology overview/Overview of the devices

“…For example, when acidic catalyst is needed in a biphasic reaction, instead of the inert static mixer and a separate catalyst, an acidic mineral with the sufficient particle size can be used in the reactor [9]. Small particles can be filled in columns or loops as well, but it is recommended to sieve the material to avoid very small particles causing plugs or high pressure drop on the system.…”