Volume 1, Issue 6

Microwave (MW) heating and conventionallyheated continuous-flow processing have emerged as viable alternatives to the traditional methods of preparing organic compounds. These tools enable the chemist to circumvent some of the issues associated with conventional processing, while improving the efficiency of chemical transformations. Recently, several strategies have been developed to perform reactions using gaseous reagents, employing MW heating or conventionally-heated microand meso-flow technologies. This perspective describes some of these strategies by means of a discussion of work performed in our laboratory, focused around alkoxycarbonylation and hydrogenation reactions.

Chirally pure 3-phenylglycidol is a key intermediate in the manufacture of a range of drugs. In order to scale up the reaction in an ionic liquid (IL)/supercritical carbon dioxide (scCO 2 ) miscibility switch system, a study was started to select the optimum IL in this case. The vanadium-catalyzed epoxidation reaction of cinnamyl alcohol to 3-phenylglycidol in the presence of imidazolium-type liquids and tert-butyl hydroperoxide (TBHP) as the oxidant was studied experimentally. Three ILs, i.e., (i) 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][Tf 2 N]), (ii) 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([bmim][TfO]), and (iii) 1-butyl-3-methylimidazolium nitrate ([bmim][NO 3 ]), ranging from hydrophobic to hydrophilic, were selected as suitable candidates in terms of viscosity and stability, and were studied as solvents in the epoxidation reaction. In accordance with previously studied catalytic oxidations in ILs, the most hydrophobic ionic liquid [bmim][Tf 2 N] results in the best yield and selectivity. Activities and product profiles are similar to those obtained in toluene, the benchmark solvent for these reactions. The maximum selectivity towards 3-phenylglycidol is 65%, with cinnamaldehyde and benzaldehyde as side products. The optimum reaction conditions require 1.5 equivalent of TBHP as the oxidant and 3 mol% of vanadyl acetylacetonate as the catalyst at 25°C. Therefore, [bmim][Tf 2 N], is a potential solvent for epoxidation reactions under miscibility switch conditions.

Direct conversion of methane to methanol is considered as a promising next-generation green technology, because it would eliminate energy intense, high temperature syngas production. Before 2000, various catalysts and thermochemical reaction systems were investigated towards converting direct methane to methanol; however, one-pass yield of methanol was <5%. More recently, bioreaction and photochemical synthesis have attracted keen attention, because these processes use renewable solar energy. However, the yield and productivity are still the main issues. This paper presents a low temperature (<600 K), direct conversion of methane to methanol/syngas via non-thermal plasma technology, which enables one-pass liquid yield of 20% (sum of CH 3 OH, HCHO and HCOOH), with selectivity between 40 and 60%. First, it emphasizes the impact of plasma catalysis in the future sustainable energy system. Second, the principle of micro-channel plasma chemical reactor is presented, then experimental results are overviewed based on our work. Finally, concluding remarks are provided.

The impact of micromixers on copolymers’ characteristics in a continuous-flow microprocess was studied. A stainless steel coiled tube was used as the microreactor. Several micromixers with different working principles, like bilamination, multilamination and impact jet, were used to mix the reactants’ streams before entering the reactor. (Co)polymers of 2-dimethyl amino ethyl methacrylate (DMAEMA) and benzyl methacrylate (BzMA) were synthesized by the atom transfer radical polymerization (ATRP) technique, with two different compositions of BzMA (20% and 40%). A faster polymerization rate was observed in case of microprocess, as compared to batch process, highlighting the inherent intensification nature of microfluidic-assisted processes. Despite equal conversion for the three micromixers, a remarkable difference in molecular weight was observed. The highest molecular weights with lowest polydispersity indices (PDIs) were obtained when the multilamination micromixer was used, while the bilamination gave polymers with high PDIs and low molecular weights. Diffusion constraints arising from the increase in viscosity was clearly visible for highest residence times in the microreactor, resulting in a deviation of molecular weight from the theoretical value.